WO2013174387A1

WO2013174387A1 - A system for obtaining an optical spectrum

Info

Publication number: WO2013174387A1
Application number: PCT/DK2013/050157
Authority: WO
Inventors: Sokol Ndoni; Fengxiao GUO; Lars Schulte
Original assignee: Danmarks Tekniske Universitet
Priority date: 2012-05-23
Filing date: 2013-05-23
Publication date: 2013-11-28

Abstract

The present invention relates to a system for obtaining an optical spectrum 648 of analytes in a fluid sample, wherein a porous filter 602a, 602b is arranged so that the fluid sample may be placed onto a first region of the porous filter, and a SERS-active material 610a, 610b having a SERS-active surface is placed at least partially within the pores of the porous filter within a second region of the porous filter. The first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region. Thereby, the porous filter enables that the fluid sample is filtered so that only sufficiently small entities in the fluid sample reach the second region where they may be probed so that an optical spectrum related to the analytes in the filtered sample may be obtained. The optical system also comprises a light source 634, a light detector 642, and the optical analysis system is arranged for obtaining the optical spectrum 648 of the analytes adjacent to the SERS-active material 610a, 610b exclusively from the second region of the porous filter 602a, 602b.

Description

A SYSTEM FOR OBTAINING AN OPTICAL SPECTRUM

FIELD OF THE INVENTION The present invention relates to a system for obtaining an optical spectrum, and more particularly to a system, database and method for providing such system and method for obtaining an optical spectrum wherein the system comprises a porous filter with a SERS active material being placed thereon. BACKGROUND OF THE INVENTION

Systems for obtaining optical spectra of analytes are interesting due to the possibility for extracting information regarding the analytes from the optical spectra.

The patent application WO 2011/029888 Al describes a sensor for detecting a drug substance from exhaled breath of a subject in-situ. Its collecting surface has a Surface Enhanced Raman Spectroscopy (SERS)-active layer of a SERS-active material. The collecting surface is arranged as an outer surface of a waveguide for contact with exhaled breath, such that at least traces of said drug substance in said exhaled breath can contact said SERS-active layer for read-out of a Raman shift spectrum.

However, an improved a system for obtaining an optical spectrum would be advantageous, such as a system for obtaining an optical spectrum which is faster, cheaper and/or simpler to construct, and in particular a more efficient and/or reliable a system for obtaining an optical spectrum would be advantageous.

The reference WO 2011/148179 Al describes a method of forming a test substrate for use with surface-enhanced Raman spectroscopy to detect at least one predetermined analyte, comprises the steps of providing a support, and adding to the support a Raman-enhancing metal surface and biological labels, wherein the labels are selected such that their Raman activity changes when they interact with said analyte. Combination of a Raman-enhancing metal surface with a selected biological label that changes its Raman activity upon interaction with an analyte facilitates detection of analytes in a highly sensitive manner. In particular it may enable detection of analytes which might not otherwise be readily detectable, and/or provide an indication of the presence of a component in the sample which might not be detectable directly. Test substrates and suspensions and methods of testing are also described.

The reference WO 2007/008151 Al describes a method of manufacturing a sensor structure which comprises providing a deposition solution in the pores of an anodic alumina membrane, distributing the deposition solution in the pores of the membrane, heating the membrane to evaporate the solvent and deposit the nano particles, cleaning the membrane and repeating the procedure until a

predetermined size and a predetermined distribution of the deposited particles have been achieved. Particles having nano dimensions can be produced by selecting the deposition solution appropriately. Deposition solutions having different compositions can be used to produce particles having a composite or layered structure, in particular, silver or palladium can used in a first deposition step to form inner portions of layered particles. The sensor structure can be used in surface enhanced Raman spectroscopy for detecting very low concentrations of various substances such as explosives. The reference US 2004/0161369 Al describes methods, systems and apparatus which concern metal impregnated porous substrates. Certain embodiments of the invention concern methods for producing metal-coated porous silicon substrates that exhibit greatly improved uniformity and depth of penetration of metal deposition. The increased uniformity and depth allow improved and more reproducible Raman detection of analytes. In exemplary embodiments of the invention, the methods may comprise oxidation of porous silicon, immersion in a metal salt solution, drying and thermal

decomposition of the metal salt to form a metal deposit. In other exemplary embodiments of the invention, the methods may comprise microfluidic

impregnation of porous silicon substrates with one or more metal salt solutions. Other embodiments of the invention concern apparatus and/or systems for Raman detection of analytes, comprising metal-coated porous silicon substrates prepared by the methods.

The reference "Optofluidic SERS on in kjet- fabricated paper-based substrates", by Ian M. White, Proc. SPIE 8264, Integrated Optics: Devices, Materials, and Technologies XVI, 826414 (February 9, 2012), describes that today a need exists to develop practical solutions for point-of-sample and point-of-rare SERS systems. In recent years, optofluidic SERS has emerged, in which microfluidic functions are integrated to improve the performance of SERS. Advancements in optofluidic SERS are leading towards portable analytical systems, but the devices are currently too expensive and too cumbersome for limited resource settings.

Recently, we demonstrated the fabrication of SERS substrates by inkjet printing silver nanostructures onto paper. Using a low-cost commercial inkjet printer, we chemically patterned cellulose paper to form hydrophobic regions, which can control the aqueous sample on the paper microsystem. Additionally we inkjet- printed silver nanoparticles with micro-scale precision to form SERS-active biosensors. Using these devices, we have been able to achieve detection limits comparable to conventional nanofabricated substrates. Furthermore, we leverage the fluidic properties to enhance the performance of the SERS devices while also enabling unprecedented ease of use. Paper dipsticks concentrate a relatively large sample volume into a small SERS-active detection region at the tip. Likewise, paper swabs collect samples from a large surface area and concentrate the collected molecules into a SERS sensor on the paper. SUMMARY OF THE INVENTION

It is a further object of the present invention to provide an alternative to the prior art. In particular, it may be seen as an object of the present invention to provide a system for obtaining an optical spectrum which is faster, cheaper and/or simpler to construct, and in particular which may be more efficient and/or reliable.

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a system for obtaining an optical spectrum of analytes in a fluid sample, the system comprising

a porous filter with pores having a pore diameter, such as a maximum pore diameter, being below 1 micrometer, such as being below 500 nm, such as being below 200 nm, such as being below 100 nm, such as being below 50 nm, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter,

a SERS-active material having a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, wherein the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, and

an optical analysis system comprising

i. a light source,

ii. a light detector, and

iii. wavelength selecting means, such as at least one optical filter,

wherein the optical analysis system is arranged for obtaining the optical spectrum of the analytes adjacent to the SERS-active material exclusively from the second region of the porous filter, such as arranged for obtaining the optical spectrum exclusively from the second region so as to exclude contributions to the optical spectrum from relatively large analytes which are too large to travel through the porous filter from the first region to the second region.

The invention is particularly, but not exclusively, advantageous for providing to the skilled person (i.e., enabling obtaining, such as fabricating or preparing) a system for obtaining an optical spectrum of analytes in a fluid sample, wherein the porous filter may serve to filter the sample and the SERS-active material may serve to enhance a signal so that the quality of the optical spectrum is improved. In particular, it may be seen as an advantage that the SERS active surface is integrated in the porous filter, since this enables a compact system, and furthermore provides the possibility that the porous filter may house the SERS- active material and/or may shape the SERS-active material so as to enhance the SERS effect.

In other words, the gist of the invention may be seen as providing an optical analysis system wherein an integrated element double functions as a mechanical filter and as an optically enhancing unity, since the structure of the porous filter may endow SERS enhancing properties to a material placed, such as deposited, thereon (such as placed onto a first region) and/or may be able to house materials with SERS enhancing properties (such as in a second region, where the optical spectrum is obtained exclusively from the second region, thereby avoiding that non-filtered material in the first region influences, such as contaminates, the optical spectrum). This (i.e., the SERS enhancement) is due to the fact that microscopic roughness, i.e., structures on the microscopic scale, of SERS active materials may enhance the SERS enhancement (or in other words, the effect of Surface Enhanced Raman Scattering may be further improved).

Light is to be broadly construed as electromagnetic radiation comprising wavelength intervals including visible, ultraviolet (UV), near infrared (NIR), infrared (IR), x-ray. The term optical is to be understood as relating to light. It is noted that the light might be in a wavelength interval which is broad or narrow, such as representing a single wavelength, such as monochromatic light. When referring to wavelength, the wavelength is understood to be the wavelength of light in free space.

A light source is understood to be a device capable of emitting light. Examples of light sources may include Light Emitting Diodes (LED's) or laser sources.

By an optical spectrum is understood information related to a plurality of wavelengths of light, such as an intensity parameter, an absorption parameter, a scattering parameter or a transmission parameter given for a plurality of wavelengths of light. It is understood that information related to light at discrete wavelengths may represent an optical spectrum. In a particular embodiment, the optical spectrum comprises a substantially continuous spectrum representative of spectral information. By a fluid sample is understood a fluid, such as gas or liquid, which may or may not comprise an analyte. Non-limiting examples include: Milk, beverages, drinking water, waste water, blood, urine, sweat, saliva or other body fluids.

By an analyte is understood a substance or chemical constituent that is of interest. It is understood that the properties, concentration, amount and/or presence of the analyte may be measured. Non-limiting examples of analytes include chemical or biological molecules, glucose, vitamins, urea and drugs, such as antibiotics. By porous filter is understood an element which is porous, i.e., which comprises a material wherein pores are located. Furthermore, the porous filter may act as a filter, i.e., being able to filter a fluid sample. Filtration is understood as the mechanical or physical operation which is used for the separation of entities above a certain size from fluids (liquids or gases) by interposing a filter, such as a multilayer lattice, such as a porous filter, through which only the fluid, and possible also smaller entities within the fluid, can pass. Large solids in the fluid are retained since they cannot pass through the filter.

In an embodiment, the porous filter is a three-dimensional structure which has a length, a width and a height, and wherein both the length and the width are larger than the height, and wherein the porous filter is arranged so that the first region and the second region are arranged on opposing sides of the porous filter which are separated by the height. An advantage of this embodiment may be, that a sample deposited on the first region is effectively separated from the second region due to the relatively large length and width, yet the analytes which are able to travel to the second region through the pores will have to only travel a relatively small distance, corresponding to approximately the height. This may be of advantage, since it may reduce the time it takes from a fluid sample is placed on the first region, and until the sufficiently small analytes may be optically probed at the second region. In a particular embodiment, the porous filter is a slab of material, such as having rectangular cross-sections.

In an embodiment, the porous filter is made substantially, such as being made of, a polymer, such as a nanoporous polymer. An advantage of this may be that it may enable control over any one of morphology, pore size, pore orientation, and that it may enable any one of high porosity, narrow pore size distribution, and easy surface functionalization.

By pore diameter is understood the effective average diameter of pores of the porous filter. The effective diameter of a pore, Dp_0re, may be defined as A 'pore

D pore 4

π

where Ap_0re is the area of the cross-section of the pore in a plane orthogonal to a n axis in a lengthwise d irection through the pore. It may be understood that the pore diameter may be substa ntia lly constant, such as consta nt, throughout the porous filter. In another em bodiment, the pore size may refer the size of the pores in a bulk portion of the porous filter. In another em bod iment, the pore size may refer the size of the pores in the second region of the porous filter.

In a n em bod iment a sensor element is presented, wherein a n effective average diameter of pores of the porous filter is sim ilar to or inferior to a wavelength, lam bda, of light transm itted through the sensor element, such as lig ht incident upon the SERS active material or em itted from the SERS active materia l .

In a n em bodiment a sensor element is presented, wherein an effective average dia meter of pores of the porous filter is inferior to, such as significantly inferior to, a wavelength, la mbda, of light transm itted through the sensor element, such as light incident upon the SERS active material or em itted from the SERS active material . If this relationship between la mbda a nd Dp_0re as outlined above is satisfied, light of wavelength lam bda travelling in the inhomogeneous m ixture of the material of the porous filter and the medium present in the pores of that element, behaves as if the light were travelling in a homogeneous medium having an effective refractive index which is ca lculated from the refractive ind ices of porous filter material a nd the medium comprised within the pores of the porous filter. In particula r, in order to behave as a materia l with an average refractive index the wavelength of light must be larger, such as significantly larger, than the length-scale of heterogeneity in the refractive index in the materia l . In a first approximation, the effective refractive index is given as a weighted average between the two refractive indices of material of the porous filter and the med ium located within the pores of the porous filter. A more accurate estimation of the effective refractive index is achieved by using e.g . the Lorentz-Lorenz m ixing rule :

Where n_efr, ηχ and n₂ are the effective refractive index, the refractive index of the filter polymer and the refractive index of the medium filling the pores,

respectively; ¼ and V₂ are the volume fractions of the two com ponents. By first region is understood a region of the porous filter onto which a fluid sam ple may be placed, such as by means of, e.g . , a pipette.

By second region is understood a region of the porous filter from which a n optical spectrum ca n be obtained, i .e. , the optica l ana lysis system is arra nged for obtaining the optica l spectrum of analytes adjacent to the SERS-active material in the second region of the porous filter, such as exclusively from the second region of the porous filter. A possible adva ntage of obta ining the optica l spectrum of analytes adjacent to the SERS-active material exclusively from the second region of the porous filter, is that the pores may ena ble the porous filter material to act as a filter by blocking entry of la rge entities, which are too large to enter into the pores due to the relatively small pore diameter. Smaller entities, however, may enter into the pores. In other words, the porous filter material may acts as a filter by blocking entities, such as fat pa rticles or other relatively la rge entities, which are not small enoug h to pass through the pores. It is understood that there may be SERS-active material present outside of the second region (for exam ple by having nanoparticles of SERS active material distributed throug hout the porous filter), but in that case the optical a na lysis system is still arra nged for obtaining the optica l spectrum of a na lytes adjacent to the SERS-active material exclusively from the second region of the porous filter, for exam ple by arranging the optica l system so that only the second region is probed, for exam ple by only illum inating the second region and/or ensuring that only light em itted from the second region is detected and contributes to the optical spectrum . In a n a lternative

em bodiment, only the second region comprises the SERS active material, so that the light sig na l em itted from the second region, due to the SERS active materia l, effectively dominates the light detected so that the optical spectrum is dom inated by the light em itted from the second reg ion .

By 'exclusively from the second reg ion' is to be understood, that the first region is substantially excluded, such as excluded, such as a sam ple placed at the first region does not contribute significantly, such as contribute, to an optical spectrum obtained exclusively from the second region.

By wherein the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, is understood that a portion of the porous filter material separates the first and the second region, but due to the through-going nature of the pores, sufficiently small analytes may still traverse the distance between the first region and the second region. It is understood that 'through-going' pores may be embodied by individual through-going pores, or may be embodied by having pores which are interconnected in a pore-network, such as with branched pores, which allows sufficiently small analytes to travel from the first region to the second region. In an embodiment the distance between the first region and the second region is at least 10 nanometer, such as at least 50 nm, such as at least 100 nm, such as at least 500 nm, such as at least 1 micrometer, such as at least 10 micrometer, such as at least 20 micrometer, such as at least 50 micrometer, such as at least 100 micrometer, such as within 10-100 micrometer. An advantage of having a relatively large distance may be that it enables a more efficient exclusion of contributions from analytes in the first region to the optical spectrum. It may be understood that the SERS enhancement happens primarily, such as only, in relatively close contact (such as sub-nm to few nm, where larger distance entails less enhancement) to the surface of the SERS enhancing material. Thus, in order to obtain signal exclusively from the second region, the second region may need to be at least 10 nm from the first region.

In an embodiment, the distance between the first region and the second region is at most 1 mm, such as at most 500 micrometer, such as at most 200 micrometer, such as at most 100 micrometer. A possible advantage of a relatively short distance may be that it takes less time for (sufficiently small) analytes to move, such as diffuse or be moved with liquid due to capillary forces, from the first region to the second region, such as enabling a relatively fast analysis. In an embodiment, the time it takes for a fluid sample, such as pure water, and/or the sufficiently small analytes (for example a solute molecule of radius 0.5 nm, representative for a number of antibiotics, which may use roughly 50% more time than water to penetrate through a pore of radius 5 nm) in the fluid sample to go from the first region to the second region, is less than 1 minute, such as less than 30 seconds, such as less than 10 seconds, such as less than 5 seconds, such as less than 2 seconds, such as less than 1 second, such as less than 500 msec, such as less than 200 msec, such as less than 100 msec, such as less than 50 msec. Another possible advantage of a relatively short distance may be that it enables minimizing adsorption of the solute (e.g., analytes) onto the pore walls, which may be critical for very low solute concentrations. For solvent molecules like water it takes about 50 ms to penetrate a 5 micron thick film; the time goes roughly like the thickness squared (200 ms for a 10 micron film).

In an embodiment, the distance between the first region and the second region is within 1-1000 micrometer, such as within 10-100 micrometer, such as within 1- 100 nanometer, such as within 5-50 nanometer, such as 10 nanometer.

It is understood that the first region and the second region are spatially

separated, i.e., physically separated, by a non-zero distance. The optical analysis system is arranged for obtaining the optical spectrum of the analytes adjacent to the SERS-active material in the second region, such as exclusively from the second region, of the porous filter, i.e., at a position away from the first region in all the mentioned cases. The distance between the first region and second region comprises porous filter, so that any entity traversing the distance from the first region to the second region goes through a portion of the porous filter separating the first region from the second region.

By a SERS-active material is understood any material which will enhance the Raman scattering of photons by analyte molecules positioned adjacent thereto. Exemplary materials include gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), titanium (Ti), or aluminium (Al).

An advantage of having a SERS active material might be that it enables carrying out Surface Enhanced Raman Scattering (SERS) and obtain SERS spectra. An advantage of SERS might be that it enables increased sensitivity. At ppm and ppb concentration levels of analytes it might not be possible to obtain normal Raman spectra at the usual optical path lengths. So SERS is better in the sense of increased sensitivity.

By a SERS-active surface is understood to be a surface which will enhance the Raman scattering of photons by analyte molecules positioned adjacent thereto. The SERS-active surface may be the surface of a SERS-active material. In particular embodiment the SERS-active surface comprises topographical structures with dimensions on the order of hundreds of nanometers, such as tens of nanometers, such as nanometers. In particular embodiment the SERS-active surface comprises topographical structures with dimensions which are relatively small compared to the wavelength of the light being emitted onto the second region by the optical analysis system. In particular embodiment the SERS-active surface comprises topographical structures with dimensions which are comparable to the pore diameter of the pores in the porous filter, such as equal to or smaller than the pore diameter of the pores in the porous filter, such as smaller than the pore diameter of the pores in the porous filter.

By (the SERS active material) being placed at least partially within the pores of the porous filter is understood that at least some portion of the SERS active material is placed at least partially within the pores of the porous filter. In a particular embodiment, coherent entities of SERS active material, such as nanoparticles of SERS active material, is placed within the pores of the porous filter. By an optical analysis system is understood any system which may enable obtaining an optical spectrum.

By a light detector is understood a detector capable of detecting light. By 'wavelength selecting means' is understood means which enables providing and/or detecting light in a narrow, limited wavelength interval. Wavelength selection means may be embodied by means of various filter systems in different positions of the optical path, such as the optical path between light source and second region and/or between the second region and the light detector, light sources emitting in different wavelength bands, or detectors for different wavelength bands.

An optical filter is understood to be an entity which allows passage of light within a certain region or regions of the optical spectrum whereas it blocks light within other wavelength regions. In the present context, the concept of an optical filter is also understood to comprise other means enabling selection of certain

wavelengths, such as diffractive gratings or prisms. In an embodiment, there is provided a porous filter with pores having a pore diameter being below 900 nm, such as below 800 nm, such as below 700 nm, such as below 600 nm, such as below 500 nm, such as below 400 nm, such as below 300 nm, such as below 200 nm, such as below 100 nm, such as below 90 nm, such as below 80 nm, such as below 70 nm, such as below 60 nm, such as below 50 nm, such as below 40 nm, such as below 30 nm, such as below 20 nm, such as below 15 nm, such as below 10 nm, such as below 5 nm, such as below 2 nm, such as below 1 nm. A possible advantage of having pores below a certain size, may be that they enable filtering of analytes above a certain size. A possible advantage of having pores below a certain size, may be that the SERS

enhancement is larger for SERS active material with features below this size, and that consequently the pores may serve as shaping elements in order to provide SERS active material with appropriately sized features.

In an embodiment, there is provided a porous filter with pores having a pore diameter being above 50 nm, such as above 40 nm, such as above 30 nm, such as above 20 nm, such as above 15 nm, such as above 10 nm, such as above 5 nm, such as above 2 nm, such as above 1 nm. A possible advantage of having pores above a certain size, may be that filtering time is kept relatively low. A possible advantage of having pores below a certain size, may be that the SERS enhancement is larger for SERS active material with features above this size, and that consequently the pores may serve as shaping elements in order to provide SERS active material with appropriately sized features.

In an embodiment, there is provided a porous filter with pores having a pore diameter being within 5-100 nm, such as within 5-50 nm, such as within 5-20 nm. In an embodiment, the pore diameter is within 5 nm-1000 nm, such as within 5 nm-500 nm, such as within 5 nm-300 nm. In an embodiment, the pore diameter is within 10 nm-1000 nm, such as within 10 nm-500 nm, such as within 10 nm- 300 nm. In an embodiment, the pore diameter is within 20 nm-1000 nm, such as within 20 nm-500 nm, such as within 20 nm-300 nm. An advantage of having the pore diameter being within certain bounds may be that the SERS effect is particularly pronounced within these bounds, which for example may enable the pores to endow a SERS active material placed thereon a relatively large SERS enhancing effect by transferring their physical dimensions to the SERS enhancing material. The SERS effect weakens both for too large (in an example, more than ~300 nm) and too small (in an example, less than 20 nm) particles. Roughly speaking for too large particles, so-called multipole electromagnetic radiation develops, and as SERS enhancement happens only through the dipole radiation, then the more multipoles are active and more energy is radiated in SERS non active modes, therefore less SERS enhancement. So particles or roughness features being too large become less efficient and the effect is too little beyond, for example, 0.5 - 1 micron. For too small particles (for example less than ~5 nm) there is not enough conductivity and the plasmons, which are collective

oscillations of conductance electrons in the metal, cannot develop properly, which again diminishes SERS enhancement. It is through plasmons that the laser light is enhanced in SERS.

In an alternative embodiment, the system for obtaining an optical spectrum of analytes comprises a plurality of light sources each of which is emitting within different wavelength bands and/or a plurality of light detectors capable of selectively detecting light within different wavelength bands. An advantage of having a plurality of light sources and/or detectors which function within different wavelength bands might be that the selection of wavelengths are given by the light sources and/or detectors, and consequently neither broad band light source nor optical filter is required.

According to another embodiment, there is provided a system, wherein the optical spectrum (648) is a Raman spectrum, such as a SERS spectrum. By a Raman spectrum is understood an optical spectrum of an analyte which enables determining the energy levels of the vibrational and/or rotational states of the analyte. An advantage of obtaining the Raman spectrum of an analyte might be that it provides insight into the chemical bonds and symmetry of molecules of the analyte. Therefore, it may provide a fingerprint by which the molecule can be identified.

According to another embodiment, there is provided a system, wherein the optical spectrum is a fluorescence spectrum. By fluorescence spectrum is understood an optical spectrum of an analyte which enables determining the energy levels of the electronic states of the analyte. An advantage of obtaining the Fluorescence spectrum of an analyte might be that it provides insight into the chemical bonds and symmetry of molecules of the analyte. Therefore, it may provide a fingerprint by which the molecule can be identified.

According to another embodiment, there is provided a system, wherein the SERS- active material is part of a layer of material in one piece, such as a coherent material, wherein said layer has dimensions being larger than the pore diameter, such as the dimensions of said layer in one or both dimensions being parallel with an outer surface of the porous filter being larger than the pore diameter, such as the dimensions of said layer in a dimension being orthogonal with a length axis of the pores being larger than the pore diameter. By a coherent material is understood a material in one piece, such as a layer of material in one piece, such as a deposited layer in one piece. The coherent material may be placed on the filter using : e-beam, sputtering, electrochemical deposition in fluid, vapor deposition, cathode sputtering, pyrolysis, ion plating.

According to another embodiment, there is provided a system, wherein the SERS- active material comprises a plurality of nanoparticles being placed within the pores of the porous filter. According to another embodiment, there is provided a system, wherein the system further comprises a processor arranged for

- Receiving the optical spectrum,

- Determining from the optical spectrum a parameter indicative of presence and/or concentration of one or more analytes in the fluid sample. An advantage of this may be that it enables interpreting the optical spectrum in a fast, straightforward and/or effective manner.

According to another embodiment, there is provided a system, wherein the porous filter is patterned into at least two different area types, where the different area types differ with respect to each other in a degree of hydrophilicity, so as to enable controlling a movement of a liquid in the fluid sample placed on the first region of the porous filter. A possible advantage of this may be that it enables guiding the fluid sample, such as a liquid in the fluid sample, placed on the first region through, e.g., hydrophilic channels in the porous filter. It is noted that this may in particular be effective when the fluid sample comprises a liquid, such as an aqueous liquid.

The term 'hydrophilicity' is used as a quantitative property, indicating how hydrophilic or hydrophobic a surface is. Specifically, when referring to

'hydrophilicity' of a surface, it is understood that a droplet of fluid on the surface can have any contact angle, including a contact angle corresponding to a hydrophilic or hydrophobic surface, i.e., a surface associated with a degree of hydrophilicity can be hydrophilic or hydrophobic. In a particular embodiment, providing a porous filter patterned into at least two different area types may be realized by carrying out the method as described in the patent application WO 2010/066782 Al which is hereby incorporated by reference in entirety. In a particular embodiment, providing a porous filter patterned into a least two different area types may be realized by carrying out by the method as described in the patent application WO 2011/0050044 Al which is hereby incorporated by reference in entirety.

According to another embodiment, there is provided a system, wherein the system comprises a plurality of second regions, and wherein the optical analysis system is arranged for obtaining optical spectra of the analytes adjacent to the SERS-active material in each of the second regions of the porous filter. An advantage of this may be that it enables obtaining, such as measuring, optical spectra corresponding to multiple analytes thus increasing the capacity of the system. Another advantage of this may be that it enables obtaining, such as measuring, optical spectra corresponding to the same type of analyte in multiple second regions, thus increasing the reliability of the system in terms of providing a reliable optical spectrum corresponding to the analyte.

According to a further embodiment, there is provided a system wherein the second regions are differently spaced with respect to the first region. In this particular embodiment, the second regions are spaced with different distances to the first region where the fluid sample is placed, and in consequence, this embodiment may be used in a similar manner as when separating analytes in chromatography. In brief, different analytes (which are still small enough to traverse through the porous filter) may travel with different speed through the porous filter depending on their characteristics, such as their interactions with the porous filter material, such as adsorption onto the material of the porous filter and/or the size. For example, analytes which adsorb strongest to the material of the porous filter are delayed the most on their way through the filter. Thus, by measuring at different distances from the first region, it may be possible to resolve the analytes (which may be detected via their respective optical spectra) with respect to their interplay with the porous filter (which in this context may be described as the 'stationary phase'), where the interplay may be related to, e.g., chemical composition and size of the analytes. It is noted that influence of characteristics, such as size, charges, etc., of the analyte on the diffusion coefficient is discussed in each of the articles "Gyroid nanoporous membranes with tunable permeability", Li et al., ACS Nano 5 (2011), 7754-7766 (see, e.g., section ^{^}Membrane Selectivity', and Table 2 and corresponding text), and "Ultrafiltration by gyroid nanoporous polymer membranes", Li et al., Journal of Membrane Science 384 (2011) 126-135.

In an embodiment there is provided a system, wherein the pore diameter is different in a bulk portion and/or the first region of the porous filter is smaller than at the second region, such as the pore diameter in a bulk portion and/or the first region of the porous filter may be 5-50 nm, such as 10-30 nm, such as the pore diameter in the second region of the porous filter may be 50-500 nm, such as 100-500 nm. It may be understood that the ranges does not include the endpoints. According to a second aspect the invention further relates to database comprising at least one predetermined optical spectrum of an analyte, wherein the

predetermined optical spectrum is determined using a system according to the first aspect. Such database may be advantageous for later comparing optical spectra from the system according to the first aspect. In the case of chemical adsorption, which is actually creating a chemical bond between the analyte and the SERS active material, new signals can appear in SERS that are absent in normal Raman. The intensities in such spectra might be specific to the type of system according to the first aspect. The database may be a computer readable storage medium, such as a hard disk drive, the storage medium may in particular embodiments be any one of volatile, non-volatile, random access, digital, magnetic, data storage devices.

According to another embodiment, there is provided a system, wherein the system further comprises a database, such as a database according to the second aspect, comprising at least one predetermined optical spectrum of an analyte. An advantage of this may be that it enables interpreting the optical spectrum in a fast, straightforward and/or effective manner. An advantage of the database being a database according to the second aspect may be that the predetermined optical spectra in the database might enable retrieving more reliable information regarding the analytes.

According to a third aspect the invention further relates to a method for providing a system for performing optical spectroscopy of analytes in a fluid sample, the method comprising the steps of

Providing a porous filter with pores having a pore diameter being below 1 micrometer, such as being below 500 nm, such as being below 200 nm, such as being below 100 nm, such as being below 50 nm, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter,

Placing a SERS-active material on the porous filter, so that the SERS active material has a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, so that the first region and the second region of the porous filter are spatially separated and connected by through- going pores so that only sufficiently small analytes are able to reach the second region, and

Placing the porous filter and the SERS-active material in an optical analysis system comprising

i. a light source,

ii. a light detector, and

iii. wavelength selecting means, such as at least one optical filter,

so that the optical analysis system is arranged for optically probing analytes adjacent to the SERS-active material exclusively from the second region of the porous filter.

An advantage of placing a SERS-active material on the porous filter may be that it enables the porous filter to double-function, i.e., to function not only as a filter but also as a housing and/or shaping element for the SERS active material. For example, if particles or a coherent layer is precipitated or deposited onto the porous filter, the topography of the SERS active material may be shaped by the physical pore structure of the porous filter, which in turn may enhance the SERS activity of the SERS active material. Thus, it may be possible to provide or enhance the SERS activity of the SERS active material in a single step by placing it onto the porous filter.

In an embodiment there is provided a method wherein placing the SERS active material on the porous filter comprises

precipitating and/or

- depositing onto the porous filter

the SERS active material, so that the topography of the SERS active material is at least partially shaped by a physical pore structure of the porous filter. In an embodiment, the SERS active material comprises particles of a SERS active material and/or a layer of SERS active material in one piece. An advantage of this embodiment may be that it becomes possible to provide or enhance the SERS activity of the SERS active material in a single step by placing it onto the porous filter (where the physical structure of the pores endows the SERS enhancing effect to the SERS active material). According to another embodiment, there is provided (presented) a method for providing (such as preparing and/or fabricating) a system that allows, such as a system suitable for, such as system arranged for, performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the steps of

- Placing a layer of SERS-active material in one piece, such as a coherent SERS-active material, wherein said layer has dimensions being larger than the pore diameter on the second region of the porous filter. According to another embodiment, there is provided a method for providing (such as preparing and/or fabricating) a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the step of

- Depositing a SERS-active material on the porous filter.

According to another embodiment, there is provided a method for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the step of

- Placing nanoparticles within the pores of the second region of the porous filter.

According to another embodiment, there is provided a method for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing nanoparticles within the pores of the second region of the porous filter, comprises any one of the steps of:

- forming nanoparticles inside the pores, such as forming the nanorparticles in situ inside the pores, such as by precipitation, such as by chemical reduction, such as by electrochemical reduction,

- placing preformed nanoparticles into the porous filter, such as by using diffusion and/or induced flow.

Nanoparticles, such as preformed nanoparticles, deposited on the surface of a porous filter material may move into the pores of the porous filter material by diffusion. Alternatively, the nanoparticles deposited on the surface of a porous filter material may move into the pores of the porous filter material by means of an induced flow, e.g., a flow induced by pressure, cf., porosimetry, or by electrical field. The nanoparticles may be preformed before entering the pores. Preforming nanoparticles may be carried out by methods known to the person skilled in the art. Alternatively, nanoparticles are commercially available and may thus readily be purchased by the skilled person. In a particular embodiment, the nanoparticles may be formed by precipitation, such as formed by precipitation within the pores, such as by the process described in the article "High-Yield Synthesis of Silver Nanoparticles by Precipitation in a High-Aqueous Phase Content Reverse

Microemulsion", Sosa et al., Journal of Nanomaterials, Volume 2010, Article ID 392572, 6 pages, which article is hereby included by reference in entirety. In an alternative embodiment, the nanoparticles may be formed, such as formed within the pores, by chemical reduction, or by electrochemical reduction, such as described in the article "Electrochemical Synthesis of Silver Nanoparticles", Rodriquez-Sanchez et al., J. Phys. Chem. B 2000, 104, 9683-9688, which is hereby incorporated by reference in entirety.

According to a fourth aspect the invention further relates to a method for obtaining an optical spectrum of a filtered sample using the system of claim 1, the method comprising :

- placing the fluid sample on the first region,

- providing a filtered sample by enabling capillary forces to draw at least a portion of the fluid sample into the porous filter so as to be placed adjacent the SERS-active material,

- obtaining the optical spectrum with the optical analysis system.

In another aspect the invention relates to use of the optical system according to the first aspect for obtaining an optical spectrum of a filtered sample. The sample may for example be any one of, e.g., milk, beverage, drinking water, waste water, blood, urine, sweat, saliva or other body fluids.

The first, second and third and fourth aspect of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE FIGURES

The system, database and method for providing such system and method for obtaining an optical spectrum according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

FIG 1 shows deposition of a material onto the porous filter,

FIG 2 shows depositing nanoparticles within the pores of the porous filter, FIG 3 shows forming of nanoparticles within the pores of the porous filter, FIG 4 shows an illustration of how an embodiment of the invention may function, FIG 5 shows the step of placing a fluid sample on the first region of a porous filter, FIG 6 shows a system for obtaining an optical spectrum,

FIGS 7-9 show measurement principles of specific embodiments,

FIG 10 shows Raman spectra from nanoporous polybutadiene of gyroid

morphology,

FIG 11 shows two pieces of nanoporous polymer immersed into milk,

FIGS 12A-B show the pieces still being wet after being taken out of the milk,

FIG 12C shows the hydrophilic polymer being wet after wiping the outer surface,

FIG 13 shows the hydrophobic piece and the hydrophilic piece after drying. DETAILED DESCRIPTION OF AN EMBODIMENT

FIGS 1-3 shows various methods for providing a SERS active material 106, 206, 308 inside the pores 104 of a porous filter material 102.

FIG 1 shows deposition of a material 106 onto the porous filter material 102. The deposition process may be embodied by any deposition process commonly known in the art, including electron-beam (e-beam) deposition, sputter deposition, electrochemical deposition in fluid, vapour deposition, chemical vapour deposition (CVD), physical vapour deposition (PVD), cathode sputtering, pyrolysis, and ion plating. It is understood that the deposited material may form a coherent layer, such as a layer of material in one piece, or may form separated islands of material on the porous filter material 102. In a particular embodiment, the material 106 may be placed within the pores of the porous filter material 102 by electrotemplating in a manner similar to the procedure described in the article "Controlled Photooxidation of Nanoporous Polymers", Ndoni et al., Macromolecules 2009, 42, 3877-3880, which article is hereby incorporated by reference in its entirety together with the corresponding Supporting Information. The article shows realization of electrotemplating of copper within the pores of a nanoporous, polymeric material.

FIG 2 shows depositing, such as positioning, nanoparticles 206 comprising a SERS active material on their surface within the pores 104, such as at least partially within the pores 104, such as completely within the pores 104 of the porous filter material 102. It is understood, that nanoparticles deposited on the surface of a porous filter material may move into the pores of the porous filter material by diffusion. Alternatively, the nanoparticles deposited on the surface of a porous filter material may move into the pores of the porous filter material by means of an induced flow, e.g., a flow induced by pressure, cf., porosimetry, or by electrical field. The nanoparticles 206 may be preformed before entering the pores 104. Preforming nanoparticles may be carried out by methods known to the person skilled in the art. Alternatively, nanoparticles are commercially available and may thus readily be purchased by the skilled person. FIG 3 shows forming the nanoparticles 308 within the pores 104, such as completely within the pores 104 of the porous filter material 102. In a particular embodiment, the nanoparticles 308 may be formed by precipitation, such as by the process described in the article "High-Yield Synthesis of Silver Nanoparticles by Precipitation in a High-Aqueous Phase Content Reverse Microemulsion", Sosa et al., Journal of Nanomaterials, Volume 2010, Article ID 392572, 6 pages, which article is hereby included by reference in entirety. In an alternative embodiment, the nanoparticles may be formed within the pores by chemical reduction, or by electrochemical reduction, such as described in the article "Electrochemical Synthesis of Silver Nanoparticles", Rodriquez-Sanchez et al., J. Phys. Chem. B 2000, 104, 9683-9688, which is hereby incorporated by reference in entirety.

It is noted that the porous filter material may be provided in a number of ways which the skilled person may employ. For example, the porous filter may be embodied by a poruos polymer, such as a nanoporous polymer. Block copolymers may be utilized in one method for preparation of porous polymers, such as block copolymer-templated porous materials. Due to the incompatibility of the constituent blocks, the block copolymers self-assemble into arrays of various well- defined structures, such as spheres, cylinders, lamellae, or more complex morphologies, with a micro domain dimension in the molecular length scale.

Nanoporous matrices can be derived from self-assembled block copolymers by partially or totally removing one block with UV, oxygen plasma, ozone, base, acid, or fluorine compounds. Alternatively, block copolymers and nanoporous matrices derived from them have been used to direct the morphology of, for example, silicas and metal oxides. Unique features like controllable morphology, pore size and orientation, high porosity, narrow pore size distribution, and easy surface functionalization render, especially the nanoporous polydiene materials, very attractive for many membrane applications. In a particular embodiment, the preparation of the porous filter material is similar to the preparation of the polymer filter membranes described in the first paragraph (entitled "Membrane preparation") of the "METHODS" section of the article "Gyroid Nanoporous Membranes with Tunable Permeability", Li et al., ACS Nano 2011 5 (10), 7754-7766, which article is hereby included by reference in entirety. It is noted that the material preparation is described in the first three paragraphs of the 'Experimental' section of the article "Nanoporous materials from stable and metastable structures of 1,2-PB-b-PDMS block copolymers" , Schulte et al., Polymer 52 (2011), 422-429, which article is hereby included by reference in entirety.

In another particular embodiment, the preparation of the porous filter material is similar to the preparation of the polymer filter membranes described in WO

2011/098090 Al, which is hereby incorporated by reference in entirety, and which describes, such as in FIGS 9A-B and corresponding text on p. 23, I. 13-28, that a porous filter material may act as a filter, such as a filter for filtering a fluid.

In another particular embodiment, the preparation of the porous filter material is similar to the preparation of the nanoporous cross-linked 1,2-polybutadiene membranes of gyroid morphology, derived from a 1,2-PB-b-PDMS block

copolymer in the article "Ultrafiltration by gyroid nanoporous polymer

membranes" , Li et al., Journal of Membrane Science 384 (2011) 126-135, which article is hereby included by reference in entirety. The article shows that the nanoporous filter materials are applicable as filters, such as filters for

ultrafiltration.

In another particular embodiment, the preparation of the porous filter material is similar to the preparation of the 1,2-Polybutadiene NP polymers which are described in the article "Nanofiltering via integrated liquid core waveguides" , Gopalakrishnan et al., Optics Letters, Vol. 36, No. 17, 3350-3352, which article is hereby included by reference in entirety. The article shows that the porous filter materials are applicable as filters, such as applicable for filtering a turbid solution, such as milk, so that propagation of light through the filtrate is possible with low transmission losses, such as similar to propagation through pure water (whereas propagation through unfiltered milk is shown to involve large transmission losses). Furthermore, the article shows that fluorescent, small particles (such as

Rhodamine B molecules of approximately 1 nm) may be in the filtrate where their fluorescent properties can be detected, and that the filter material can block entry of larger particles (such as 22 nm beads). Two other techniques that may be employed to create nanoporous polymeric films are phase separation and ion-track etching.

FIG 4 shows an illustration of how an embodiment of the invention may function. In the middle part of FIG 4 is shown a porous filter material 102a whereupon a SERS active material 410a has been deposited. The thickness 422 of the porous filter material 102a may in exemplary embodiments be within 1-1000 micrometer, such as within 10-100 micrometer. The thickness 424 of the deposited SERS active material 410a may in exemplary embodiments be within 1-100 nanometer, such as within 5-50 nanometer, such as 10 nanometer. The circle 412 denotes a region which comprises a portion of the first region, which is shown in an enlarged version in the upper part of FIG 4. The circle 414 denotes a region which comprises a portion of a second region, which is shown in an enlarged version in the bottom part of FIG 4.

In the upper part of FIG 4 is shown a portion 102b of the porous filter material with individual pores 104b. The pore diameter 421 of the pores is less than 1 micrometer, such as being below 500 nm, such as being below 200 nm, such as being below 100 nm, such as being below 50 nm. With such limited pore diameter, the pores may enable the porous filter material to act as a filter by blocking entry of large entities, such as the entity 420, which is too large to enter into the pore. Smaller entities, such as the smaller entity 418 may enter into the pores. In other words, the porous filter material may acts as a filter by blocking entities, such as fat particles or other relatively large entities, which are not small enough to pass through the pores.

In the bottom part of FIG 4 is shown a portion 102c of the porous filter material and a portion 410c of the SERS active material. In this enlarged view, it is possible to see individual pores 104c. Furthermore, it is possible to see that the deposited SERS active material 410a has entered into the pores 104c so that it forms small structures 416 which have a limited size due to the limited size of the pores. The smaller structures 416 may enable enhancement of a Raman signal, since roughness on the scale of the pore diameter may be beneficial for enhancing the Raman signal. In consequence, small entities 418, such as a small molecule, may be probed using Raman, and due to the enhancement may be detected with higher accuracy, precision and/or lower detection limit.

FIG 5 shows the step of placing with a pipette 526 a fluid sample 528 on the first region of a porous filter material 502. In this embodiment, the first region corresponds to the upper surface of the filter material 502, i.e., the surface onto which the fluid sample 528 is placed. On the opposite side of the porous filter material is deposited a SERS active material 510. The rectangle 530 corresponds to a region which is shown enlarged on the left side in the image 530. The scale bar 532 corresponds to 100 nm.

FIG 6 shows a system for obtaining an optical spectrum 648, such as Raman spectrum or a fluorescence spectrum, of analytes in a fluid sample, such as a liquid sample or a gaseous sample, the system comprising

- a porous filter 602a, 602b with pores having a pore diameter being below 1 micrometer, such as being below 500 nm, such as being below 200 nm, such as being below 100 nm, such as being below 50 nm, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter,

- a SERS-active material 610a, 610b having a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, wherein the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, and

- an optical analysis system comprising

i. a light source 634,

ii. a light detector 642, and

iii. wavelength selecting means, such as an optical filter 638,

wherein the optical analysis system is arranged for obtaining the optical spectrum 648 of the analytes adjacent to the SERS-active material 610a, 610b exclusively from the second region of the porous filter 602a, 602b.

In the figure, the light source 634 emits broad band light 636 and the wavelength selecting means is embodied by an optical filter 638 which selects a specific wavelength so that narrow band light is 640 is used for probing the analytes in the first region of the porous filter material. However, the wavelength selecting means may also be realised by other means known in the art, for example a tunable light source, such as a tunable laser, or an optical filter being in the path of the light between the first region of the porous filter material 602a, 602b and the detector 642. The detector 642 may be part of a commercial Raman spectrometer 644 which may be relatively compact cf., the scale bar 646 which corresponds to 10 centimetres. One possible advantage of the setup shown in FIG 6 is that the LASER light is confined within two outer metal SERS substrates 610a, 610b, and multiple scattering of the LASER light may further reinforce the SERS response.

FIGS 7-9 show measurement principles of specific embodiments.

FIG 7 shows an embodiment similar to the embodiment depicted in FIG 4, where incoming light 740 propagates through the porous filter material 102a and is incident upon the SERS active material 410a. Analytes being placed adjacent to the SERS active material 410a may give rise to surface enhanced Raman scattering which may be seen as emitted electromagnetic radiation 741a on the same side of the porous filter material or which may be seen as emitted

electromagnetic radiation 741b on the opposite side of the porous filter material. In either way, the emitted electromagnetic radiation (741a and/or 741b) may in turn be detected and give rise to an optical spectrum which may be indicative of the presence (and potentially quantity) of the analytes. In the present

embodiment, the first region may be the upper surface or upper region, such as the surface and region encircled by circle 712, and the second region may be the lower surface of the region at the interface between porous filter material 102a and deposited SERS active material 410a. The distance between the first region and the second region may thus correspond to the thickness 422 of the porous filter material 102a. FIG 8 shows an embodiment similar to the embodiment of FIG 7, except that instead of having a layer of SERS active material deposited on the porous filter material 802, nanoparticles 810 are embedded into the pores of the porous filter material within a second region with thickness 824. Incoming light 840

propagates through the porous filter material 802 as in the embodiment in FIG 7 and is incident upon the SERS active material 810. Analytes being placed adjacent to the SERS active material 810 may give rise to surface enhanced Raman scattering which may be seen as emitted electromagnetic radiation 841a, 841b, which may in turn be detected and give rise to an optical spectrum which may be indicative of the presence (and potentially quantity) of the analytes.

FIG 9 shows an embodiment similar to the embodiment in FIG 8 except that the nanoparticles 910 are distributed throughout the porous filter material 902, and that the incoming light 940 is arranged for only probing a relatively short distance 924 into the porous filter material. Thus the lower portion of the porous filter material 902 being below the dotted line may be seen as a second region, and the upper portion, such as the upper surface, or the region adjacent the upper surface, may be seen as the first region. The first region is separated by the lower region by distance 922. FIG 9 also shows a pipette 926 placing a fluid sample 928 on the first region of a porous filter material 902. In embodiments depicted in FIGS 7-9, the probing light as well as the emitted light may be arranged to propagate only across a relatively short distance within the porous material, which may be advantageous since a large path length within the porous material may generate a background signal from Raman scattering from the porous material and solute or gas which will overlap with the SERS signal from the second region.

EXAMPLES

EXAMPLE 1 - Obtaining Raman Spectra

FIG 10 shows Raman spectra of 1 mM biphenyl-4-thiol in ethanol solution deposited on top of a nanoporous polybutadiene of gyroid morphology.

The lower spectrum 1050 at the bottom is for the sample without the SERS enhancing substrate, while the upper two spectra show SERS signals of similar enhancement produced by either gold sputtering (middle spectrum 1052) or silver e-beam evaporation (upper spectrum 1054). The spectra were shifted vertically for clarity.

Obtaining the Raman spectra The shown measurements were done on a DXR Raman microscope from Thermo Scientific with a 10X objective operating with a 780 nm or 540 nm lasers. The Raman measurement conditions are: 1 mM biphenyl-4-thiol in ethanol solution, laser wavelength of 780 nm, 0.1 mW power recorded for 10 seconds, spot diameter of laser on the sample is 3.1 μηη.

Electron beam (E-beam) evaporation

Electron beam evaporation of silver or gold was performed on Alcatel SCM600 with deposition rates of 1-10 A/s at a pressure of 2- 10^"6 mbar. The sample showing the upper (grey line) SERS signal in the figure was covered with 40 nm of silver on one side at a deposition rate of 1 A/s.

Sputter coating

The sputter coating was done in a Cressington Sputter Coater 208 HR under Argon with pressure of 0.1 bar; Ar: Instrument Argon 5.0 from AGA. The current can be varied in the range 0-100 mA. The sputtering of gold for the sample showing the middle (blue) SERS signal in FIG 10 was done for 57 s at 60 mA.

EXAMPLE 2 - Filtering milk

FIGS 11-13 demonstrates the filtering properties of a nanoporous polymer, and more particularly shows filtration of milk through hydrophilic nanoporous cross- linked 1,2-PB.

FIG 11 shows two pieces of nanoporous polymer, one hydrophobic 1156 and the other hydrophilic 1158 which are both immersed into milk 1162. After 1 min a rising clear meniscus 1160 is observed in the case of the hydrophilic polymer piece. This is part of milk's whey entering the pores and rising by capillary forces.

FIGS 12A-B show the pieces still being wet after being taken out of the milk. A clear liquid 1260 fills the hydrophilic pores.

FIG 12C shows the hydrophilic polymer still being wet after wiping the outer surface. After wiping the outer surfaces of the samples the hydrophobic piece does not show any mass uptake, while the hydrophilic piece shows a mass uptake consistent with a liquid similar to water filling the pores up to the meniscus. After wiping the outer surfaces with a wet tissue the two samples are dried.

FIG 13 shows that after drying the hydrophobic piece 1156 remains completely transparent, while the hydrophilic piece 1158 becomes hazy in the region previously filled by the clear liquid. The haziness is ascribed to crystallites formed inside the nanopores mainly from whey sugars, which constitute the largest part of whey's dry mass.

FIG 14 shows an illustration of an embodiment of the invention similar to FIG 4, except that in the present figure, the pores 1404 (of the porous filter of porous filter material 1402) have a non-constant pore-size, such as pore diameter. More particularly, in the present embodiment, the pore diameter is different in a bulk portion and/or the first region of the porous filter than at the second region, such as at a surface of the porous filter where SERS active material 1410 may be deposited. An advantage of this may be, that it enables tailoring the pore size(s) to suit different requirements, such as

- the pore diameter in the bulk of the porous filter 1402 being optimized with respect to a filtering effect (such as enabling filtering a certain size of analytes) and/or optimized with respect to filtering time (such as the time it takes for fluid and analytes to flow in direction 1464 from the first region to the second region), and/or

- the pore diameter in the second region being optimized so as to enable shaping the SERS active material 1410 in order to optimize the SERS enhancing effect.

In other words, an advantage of such embodiment may be that optimal filtering and/or optimal SERS enhancement may be achieved. In a particular embodiment, the pore diameter may be larger in the second region compared to a pore diameter in a bulk portion of the porous filter. In embodiments, the pore diameter in a bulk portion and/or the first region of the porous filter may be 5-50 nm, such as 10-30 nm. In embodiments, the pore diameter in the second region of the porous filter may be 50-1000 nm, such as 100-500 nm. The a porous filter with non-constant pore sizes may be provided according to, for example, the reference "Selective Separation of Similarly Sized Proteins with Tunable Nanoporous Block Copolymer Membranes", Xiaoyan Qiu et al., ACS Nano, 2013, 7 (1), pp 768-776, which is hereby incorporated by reference in entirety.

To sum up, there is presented a system for obtaining an optical spectrum 648 of analytes in a fluid sample, wherein a porous filter 602a, 602b is arranged so that the fluid sample may be placed onto a first region of the porous filter, and a SERS-active material 610a, 610b having a SERS-active surface is placed at least partially within the pores of the porous filter within a second region of the porous filter. The first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region. Thereby, the porous filter enables that the fluid sample is filtered so that only sufficiently small entities in the fluid sample reach the second region where they may be probed so that an optical spectrum related to the analytes in the filtered sample may be obtained. The optical system also comprises a light source 634, a light detector 642, and the optical analysis system is arranged for obtaining the optical spectrum 648 of the analytes adjacent to the SERS-active material 610a, 610b in the second region, such as exclusively from the second region, of the porous filter 602a, 602b. In exemplary embodiments E1-E15, the invention may relate to:

El. A system for obtaining an optical spectrum (648) of analytes in a fluid

sample, the system comprising

a porous filter (602a, 602b) with pores having a pore diameter being below 1 micron, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter, a SERS-active material (610a, 610b) having a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, wherein the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, and

an optical analysis system comprising

iv. a light source (634),

v. a light detector (642), and vi. wavelength selecting means, such as at least one optical filter (638),

wherein the optical analysis system is arranged for obtaining the optical spectrum (648) of the analytes adjacent to the SERS-active material (610a, 610b) in the second region of the porous filter (602a, 602b).

E2.A system according to embodiment El, wherein the optical spectrum (648) is a Raman spectrum.

E3.A system according to any of the preceding embodiments, wherein the

SERS-active material (602a, 602b) is part of a layer of coherent material with dimensions being larger than the pore diameter.

E4.A system according to any of the preceding embodiments, wherein the

SERS-active material comprises a plurality of nanoparticles (206, 308) being placed within the pores of the porous filter (102).

E5.A system according to any of the preceding embodiments, wherein the

system further comprises a processor arranged for

- Receiving the optical spectrum (648),

Determining from the optical spectrum a parameter indicative of presence and/or concentration of one or more analytes in the fluid sample.

E6.A system according to any of the preceding embodiments, wherein the

porous filter (602a, 602b) is patterned into at least two different area types, where the different area types differ with respect to each other in a degree of hydrophilicity, so as to enable controlling a movement of a liquid in the fluid sample placed on the first region of the porous filter.

E7.A system according to any of the preceding embodiments, wherein the

system comprises a plurality of second regions, and wherein the optical analysis system is arranged for obtaining optical spectra of the analytes adjacent to the SERS-active material (610a, 610b) in each of the second regions of the porous filter.

E8.A database comprising at least one predetermined optical spectrum of an analyte, wherein the predetermined optical spectrum is determined using a system according to embodiment El.

E9.A system according to any of embodiments E1-E7, wherein the system

further comprises a database, such as a database according to embodiment E8, comprising at least one predetermined optical spectrum of an analyte.

E10. A method for providing a system for performing optical spectroscopy of analytes in a fluid sample, the method comprising the steps of

- Providing a porous filter (602a, 602b) with pores having a pore

diameter being below 1 micron, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter,

- Placing a SERS-active material (610a, 610b) on the porous filter, so that the SERS active material has a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, so that the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, and

- Placing the porous filter and the SERS-active material an optical analysis comprising

i. a light source (634),

ii. a light detector (642), and

iii. wavelength selecting means, such as at least one optical filter (638),

so that the optical analysis system is arranged for optically probing analytes adjacent to the SERS-active material in the second region of the porous filter. Ell. A method according to embodiment E10, for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the steps of

Placing a layer of coherent SERS-active material with dimensions being larger than the pore diameter on the second region of the porous filter.

E12. A method according to any one of embodiments E10-E11, for

providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the step of

Placing nanoparticles within the pores of the second region of the porous filter.

E13. A method according to any one of embodiments E10-E12, for

Depositing a SERS-active material on the porous filter.

E14. A method according to embodiment E12, for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing nanoparticles within the pores of the second region of the porous filter, comprises any one of the steps of:

- forming nanoparticles inside the pores,

- placing preformed nanoparticles into the porous filter.

A method for obtaining an optical spectrum of a filtered sample ing the system of embodiment El, the method comprising :

placing the fluid sample on the first region,

- obtaining the optical spectrum with the optical analysis system. Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. A system for obtaining an optical spectrum (648) of analytes in a fluid

sample, the system comprising

a porous filter (602a, 602b) with pores having a pore diameter being below 500 nm, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter, a SERS-active material (610a, 610b) having a SERS-active surface being placed at least partially within the pores of the porous filter within a second region of the porous filter, wherein the first region and the second region of the porous filter are spatially separated and connected by through-going pores so that only sufficiently small analytes are able to reach the second region, and

an optical analysis system comprising

- a light source (634),

- a light detector (642), and

- wavelength selecting means, such as at least one optical filter (638),

characterized in that

the optical analysis system is arranged for obtaining the optical spectrum (648) of the analytes adjacent to the SERS-active material (610a, 610b) exclusively from the second region of the porous filter (602a, 602b).

2. A system according to claim 1, wherein the pore diameter is within 5 nm- 300 nm.

3. A system according to claim 1, wherein the pore diameter is below 70 nm.

4. A system according to claim 1, wherein the porous filter is a three- dimensional structure which has a length, a width and a height, and wherein both the length and the width are larger than the height, and wherein the porous filter is arranged so that the first region and the second region are arranged on opposing sides of the porous filter which are separated by the height.

5. A system according to claim 1, wherein the porous filter is being made substantially of a polymer.

6. A system according to claim 1, wherein the optical spectrum (648) is a

Raman spectrum.

7. A system according to any of the preceding claims, wherein the SERS-active material (610a, 610b) is part of a layer of material in one piece wherein said layer has dimensions being larger than the pore diameter.

8. A system according to any of the preceding claims, wherein the SERS-active material comprises a plurality of nanoparticles (206, 308) being placed within the pores of the porous filter (102).

9. A system according to any of the preceding claims, wherein the system

further comprises a processor arranged for

- Receiving the optical spectrum (648),

10. A system according to any of the preceding claims, wherein the porous filter (602a, 602b) is patterned into at least two different area types, where the different area types differ with respect to each other in a degree of hydrophilicity, so as to enable controlling a movement of a liquid in the fluid sample placed on the first region of the porous filter.

11. A system according to any of the preceding claims, wherein the system

comprises a plurality of second regions, and wherein the optical analysis system is arranged for obtaining optical spectra of the analytes adjacent to the SERS-active material (610a, 610b) in each of the second regions of the porous filter.

12. A system according to any of the preceding claims, wherein the pore

diameter is different in a bulk portion and/or the first region of the porous filter is smaller than at the second region, such as the pore diameter in a bulk portion and/or the first region of the porous filter may be 5-50 nm, such as 10-30 nm, such as the pore diameter in the second region of the porous filter may be 50-500 nm, such as 100-500 nm.

13. A database comprising at least one predetermined optical spectrum of an analyte, wherein the predetermined optical spectrum is determined using a system according to claim 1.

14. A system according to any of claims 1-12, wherein the system further

comprises a database, such as a database according to claim 13, comprising at least one predetermined optical spectrum of an analyte.

15. A method for providing a system for performing optical spectroscopy of analytes in a fluid sample, the method comprising the steps of

- Providing a porous filter (602a, 602b) with pores having a pore

diameter being below 500 nm, the porous filter being arranged so that the fluid sample may be placed onto a first region of the porous filter,

i. a light source (634),

ii. a light detector (642), and

iii. wavelength selecting means, such as at least one optical filter (638),

characterized in that the optical analysis system is arranged for optically probing analytes adjacent to the SERS-active material exclusively from the second region of the porous filter.

16. A method according to claim 15, wherein placing the SERS active material on the porous filter comprises

- precipitating and/or

- depositing onto the porous filter

the SERS active material, so that the topography of the SERS active material is at least partially shaped by a physical pore structure of the porous filter.

17. A method according to any one of claims 15-16, for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the steps of

Placing a layer of SERS-active material in one piece wherein said layer has dimensions being larger than the pore diameter on the second region of the porous filter.

18. A method according to any one of claims 15-17, for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the step of

19. A method according to any one of claims 15-18, for providing a system for performing optical spectroscopy of analytes in a fluid sample, wherein the step of placing a SERS-active material on the porous filter, comprises the step of

Depositing a SERS-active material on the porous filter.

20. A method according to claim 18, for providing a system for performing

optical spectroscopy of analytes in a fluid sample, wherein the step of placing nanoparticles within the pores of the second region of the porous filter, comprises any one of the steps of:

- forming nanoparticles inside the pores,

- placing preformed nanoparticles into the porous filter.

21. A method for obtaining an optical spectrum of a filtered sample using the system of claim 1, the method comprising :

placing the fluid sample on the first region,

- obtaining the optical spectrum with the optical analysis system.