WO2003096876A2 - Continuously operational diagnostic device - Google Patents

Abstract

A diagnostic system, in the form of a device worn which can be worn under the eyelid of elsewhere is provided to permit convenient self monitoring of body conditions. The system includes sensing material which exhibits a color change in response to the changing level of a selected substance contained in body fluids which is also found in the tears. The diagnostic sensing system preferably includes sensor material formed as a crystalline colloidal array (CCA) polymerized in a hydrogel.

Description

CONTINUOUSLY OPERATIONAL DIAGNOSTIC DEVICE

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Provisional Application Serial No.

60/259,775, filed on January 4, 2001.

BACKGROUND OF THE INVENTION

The invention relates generally to diagnostic devices and more particularly

to devices for continuously monitoring the levels of selected substances in body fluids.

Various medical conditions, such as diabetes, glacuoma, bacterial infection, drug use, and others, require periodic monitoring of the level of selected component in body fluids. For example, individuals with diabetes should periodically monitor their blood glucose levels. The most common way for an individual to measure their blood glucose level is with a finger stab to draw blood, followed by the use one of the many devices available to determine the blood glucose level in the blood.

Many patients find drawing blood or other body fluids to monitor the level of selected components in body fluids to be unsatisfactory. For example, the pain, inconvenience and cost of conventional testing methods commonly lead to non- compliance at least with respect to the frequency of testing. For example, individuals who should monitor their blood glucose levels 4 times a day, might only draw blood 2-3 times a day. This can lead to undesirable health consequences.

Accordingly, it is desirable to provide improved methods and systems for monitoring the level of selected components in body fluids, such as a method and device

1066264vl permitting individuals with diabetes to monitor their blood glucose level, in a more convenient manner, which overcome inadequacies of the prior art.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the invention, a diagnostic system, in the form of a device worn which can be worn under the eyelid or elsewhere is provided to permit convenient self monitoring of body conditions. The system includes sensing material which exhibits a color change in response to the changing level of a selected substance contained in body fluids which is also found in the tears. The diagnostic sensing system preferably includes sensor material formed as a crystalline colloidal array (CCA) polymerized in a hydrogel. As used herein, hydrogels are materials having the capability of shrinking or swelling in response to specific stimuli. As the hydrogel shrinks or swells, the lattice structure of the CCA embedded therein changes. This change in lattice structure affects the wavelength of light diffracted by the CCA. Thus, by monitoring the change in diffracted wavelength such as by monitoring the color of the diagnostic system, the effects of the stimulus on the hydrogel will correlate to the level of the stimulus, such as glucose in the tears. This level can be proportional to the concentration of the stimulus in the blood. Thus, by selecting a hydrogel that shrinks and swells in response to a substance who's concentration in body fluid is to be monitored, the hydrogel can be used to monitor the concentration of the substance, such as glucose, in a body fluid, such as blood.

The sensing material can be inserted in or on the body, such as between the eyelid and the eyeball. The sensing material can also be held in a carrier. One preferred carrier for the CCA polymerized in a hydrogel is an insert that can be worn on the eyeball, said insert capable of exchanging tear fluids between the eye and the sensor material contained therein. Such a carrier can be in the form of a contact lens worn over the iris and pupil, in which the sensor material can be at the periphery or an another portion thereof. Another embodiment involves the use of an insert worn under the eyelid, the color of which can be checked by retracting the lower eyelid.

Diagnostic systems in accordance with the invention are advantageously used in conjunction with a mirror having colors thereon, the colors associated with numerical values correlated to concentration levels of the substance of interest. As a user looks into the mirror, they can match the color of the sensing material with the color on the mirror and read the numerical value (or other description, such as high, low or normal) associated with the color. In certain preferred embodiments of the invention, the mirror can also include a light, such as one shining at a selected angle and/or wavelength, wherein the sensor material remains a color that is substantially unnoticeable, but which, when illuminated the light of the selected wavelength and/or angle, turns a noticeable color corresponding to the level of the material being monitored.

Accordingly, it is an object of the inventor to provide an improved monitoring system and method, which are more convenient to use than those of the prior art.

Other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus or system embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure and the scope of the invention will be indicated in the claims. BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to the following description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a demonstrative view of a sensor in accordance with the invention inserted below the iris;

FIG. 2 is a demonstrative view of a mirror for use in accordance with the invention, for a user to check the color of a sensor in their eye;

FIG. 3 is an illustration of monomers advantageously used in a hydrogel according to preferred embodiments of the present invention;

FIG. 4 is a cross sectional view of a diagnostic system in accordance with an embodiment of the invention;

FIG. 5 is a front view of a diagnostic system in accordance with the invention inserted between the lower eyelid and the eye of a user;

FIG. 6 is a cross sectional view taken along line 6-6 of FIG. 5; and

FIGS. 7 A, 7B and 7C are demonstrative views showing the change in CCA dimensions as receptors in the hydrogel are bound to the selected stimulus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Diagnostic systems in accordance with the invention include sensor material, which reversibly and continuously changes color in response to the change in concentration of a selected substance in contact with the sensor material. For example, if the selected substance is glucose, the sensor will continuously change the wavelength (color) of reflected/refracted light, when illuminated with ambient light or light of a selected orientation, wavelength or angle, and each color change will be associated with a change in glucose concentration. It has been found that the change in glucose concentration in the tears is substantially proportional to its varying level in the blood at least over the relevant ranges. Thus, by continuously contacting the sensing material with tear fluid and observing color changes or detecting wavelength changes with appropriate instruments, the sensor can continuously monitor blood glucose levels.

Preferred sensing devices comprise crystalline colloidal array (CCA) materials polymerized in a hydrogel which shrinks or swells in response to a specific stimuli, the-stimuli corresponding to the substance to be monitored. As the hydrogel shrinks or swells, the lattice structure of the CCA embedded therein changes. As the lattice structure changes, the wavelength of light (color) diffracted by the CCA changes. Thus, by monitoring the change in diffracted wavelength, i.e., change in color of the sensor, the concentration of a particular substance in a body fluid in contact with the sensor can be determined. Thus, depending on how the sensor is constructed, increased levels of the selected substance can lead to an increase in the wavelength of reflected light, or in alternate constructions, the sensor will exhibit a decrease in the wavelength of reflected light. The gels can be modified, so as to be selective for specific body substances.

The sensor can be placed directly on the body, such as between the eyelid and the eyeball. For example, the sensor can be contained in or a biocompatible carrier. The sensor can also be contained in or on a carrier capable of being worn on the eyeball. Such carrier material can be in the form of a contact lens worn over the iris and pupil, in which the sensor material is contained around the periphery thereof. So as not to give the wearer an unusual appearance, the sensor material can be selected so as to be an unnoticeable color when exposed to ordinary light, but exhibit noticeable wavelength changes when illuminated with light of a selected angle and/or wavelength, or band of wavelengths, such as light in the ultraviolet region. In preferred embodiments of the invention, the wavelength change is most noticeable when illuminated with columnated light. As still another example, the sensor material can be inserted subcutaneously and the color change can be viewed through the skin. In the case of a subcutaneous implant, the sensor can be selected so as to exhibit wavelength changes when subjected to infra red radiation. Such wavelength changes could be detected with an appropriate wavelength detection instrument.

In a preferred embodiment of the invention, the sensing material, with or without the carrier material, can be constructed to be worn below the iris, to be ordinarily hidden by the lower eyelid, such that monitoring can be accomplished by simply retracting the eyelid to expose the carrier. This embodiment has the advantage of being concealed during normal use. Thus, it can be worn all day. Alternatively, it can be put in place periodically, for periodic monitoring.

Viewing mirrors in accordance with preferred embodiments of the invention can be formed with colors thereon to match the color changes of the sensor. One preferred mirror is circular and the colors are arranged in an annular ring for easy monitoring. The mirror can also be coupled to a light for enhanced viewing and color matching. Additional information, such as numerical or textual information can be provided to correspond to the color to the condition being monitored. For example, the concentration of blood glucose can be associated with the corresponding colors. Alternatively, more descriptive text can be provided, such as associating colors with conditions such as hyperglycemia, normal or hypoglycemia.

In one embodiment of the invention, the change in wavelength is detected with a wavelength detection instrument. A box can be constructed with a viewing "bull's eye" that a user looks at, preferably through a hole or tube to properly orient the eye to a light source of the box. The light, preferably a columnated light source can then be used to illuminate the sensor in the eye. Light will be reflected back to the box and the wavelength of such light can be measured and displayed. The display can also report the level of the monitored substance or other information about the level of the substance detected, such as high, low, normal or none. In one embodiment of the invention, the box can also include the type of mirror discussed below and a user can use the mirror for a quick check and the instrumentation for a more accurate reading when desired.

An example of an ocular insert carrier for use in a diagnostic system in accordance with a preferred embodiments of the invention is shown generally as ocular inserts 100a, 100b and 100c in FIG. 1. Alternatively, sensor material in the shape and location as inserts 100a- 100c can be used. As can be seen, ocular insert lOOa-c is worn under the iris and can be checked in a mirror by pulling down the lower eyelid. In one preferred embodiment of the invention, ocular insert 100a, exposed to tear glucose levels corresponding to low blood glucose levels could appear purple, ocular insert 100b, exposed to tear glucose levels corresponding to normal blood glucose levels could appear blue and ocular insert 100c, exposed to tear glucose levels corresponding to high blood glucose levels could appear red.

An example of a mirror to be used in a diagnostic system in accordance with preferred embodiments of the invention is shown generally as mirror 200 in FIG. 2. Mirror 200 includes an annular ring 210, segmented into color sections corresponding to the colors a user of an ocular diagnostic system in accordance with the invention would encounter. Next to the individual colors is an indication of the blood glucose level. For example, a yellow color could indicate 260 mg/dl or simply high glucose. Likewise, next to a blue color, the mirror can state 120 mg/dl or simply "normal".

Sensor material for use in accordance with preferred embodiments of the invention is described in U.S. Patent No. 5,854,078, the contents of which are incorporated herein by reference. Devices in which a CCA is embedded in a polymer matrix, have also been disclosed in U.S. Pat. Nos. 5,368,781, 5,266,238, 5,330,685, 5,338,492 and 5,342,552, the contents of which are incorporated by reference.

An optical sensor that utilizes the concept of pH-dependent swelling of special polymers is discussed in Schalkhammer, et al., "The Use of Metal-island-coated pH Sensitive Swelling Polymers for Biosensor Applications", Sensors and Actuators B, Vol. 24-25, pp. 166-172 (1995). Conductimetric sensor devices have been proposed based on the selective swelling of hydrogels in response to pH by Sheppard, "Design of a Conductimetric Microsensor Based on Reversibly Swelling Polymer Hydrogels", Transducers '91, 773-776 (1991) and Sheppard, et al, "Microfabricated Conductimetric pH Sensor", Sensors and Actuators B, Vol. 28, pp. 95-102 (1995). Sensor devices based on the selective swelling of hydrogels in response to glucose have been proposed by McCurley, "An Optical Biosensor Using A Fluorescent, Swelling Sensing Element", Biosensors and Bioelectronics, Vol. 9, pp. 527-533 (1994) and Kikuchi, et al., "Glucose- Sensing Electrode Coated With Polymer Complex Gel Containing Phenylboronic Acid", Anal. Chem., Vol. 68, pp. 823-828 (1996). The contents of these references are also incorporated herein by reference. However, none of the art discloses a sensor device that utilizes crystalline colloidal array diffraction as a diagnostic monitoring device in the manner disclosed herein.

Hydrogels in accordance with preferred embodiments of the invention undergo a volume change in response to a specific chemical species. Because the volume of the hydrogel changes, the lattice spacing of a CCA embedded therein changes as well. The light diffraction properties of the CCA change as the lattice spacing is changed. Measuring the change in diffraction, therefore, indicates the presence or absence of the stimuli that causes the volume of the hydrogel to change.

Diagnostic systems of the present invention can be used to detect a number of specific stimuli. For example, they can be used to detect the presence of various chemicals, such as metal ions in solution and organic molecules such as glucose, making the sensing material useful for chemical analysis. The sensing material can also be used to detect the presence of various gasses in solution. As a biomedical detection device, these sensors can be used to detect the presence of antigens from various sources, antibodies from various sources, and viruses such as HIV.

Monodisperse, highly charged colloidal particles dispersed in very low ionic strength liquid media self-assemble due to electrostatic repulsion to form CCA. These ordered structures can be either body-centered cubic (BCC) or face-centered cubic (FCC) arrays with lattice constants in the mesoscale range (50-500 nanometers (nm)). Just as atomic crystals diffract x-rays meeting the Bragg condition, CCA diffract ultraviolet (UV), visible and near infrared (IR) light. CCA can be prepared as macroscopically ordered arrays from non-close packed spheres. Such arrays exhibit highly efficient Bragg diffraction; nearly all light meeting the Bragg condition is diffracted, while adjacent spectral regions not meeting the Bragg conditions will freely transmit. "Non-close packed spheres" refers to an ordering wherein the spheres are spaced by some distance from each other. The Bragg diffraction law is represented by the following formula:

mλ = 2 nd sinθ

where m is the order of diffraction, λ is the wavelength of incident light, n is the suspension refractive index, d is the interplanar spacing, and θ is the angle between the incident light and the crystal planes.

Certain polymers reversibly change conformation in response to a specific external stimulus. For example, almost all polymers undergo some reversible conformational change with changes in solvents, and some, such as poly N- isopropylacrylamide, undergo conformational changes in response to temperature changes. Solutes that interact with the side groups on the polymer backbone may also induce conformational changes; introduction of ionized groups onto the backbone of the polymer thus sensitizes the polymer conformation to changes in ionic strength. Polymers that change conformation in response to the concentration of a single, specific solute can therefore be prepared by adding to that polymer a functional group that selectively interacts with that single solute. Such polymers can be further mixed with crosslinking agents to form gels that exhibit the same response to stimuli as the polymer from which they are formed. For example, these gels will undergo volume changes at conditions when the constituent polymer chains change conformation. Volume changes between 0.1 and 50%, or even greater, are contemplated by the present invention. The volume response exhibited by these hydrogels allows for their broad application in areas including but not limited to chemomechanical systems, separation devices and sensor devices.

Sensors of the present invention can be formed with: a hydrogel characterized by the property of undergoing a volume change in response to a specific chemical species; and a light diffracting crystalline colloidal array of charged particles polymerized in said hydrogel; said crystalline colloidal array having a lattice spacing that changes when said volume of said hydrogel changes, thereby causing the light diffraction of the crystalline colloidal array to change.

The hydrogel in one embodiment of the present invention generally comprises a crosslinking agent, a gel component and a molecular recognition component. The crosslinking agent can be any crosslinking agent compatible with the other components of the hydrogel. Examples of suitable crosslinkers include N,N'- methylenebisacrylamide, methylenebismethacrylamide and ethyleneglycol- dimethacrylate, with N,N'methylenebisacrylamide being preferred. In addition to forming the polymer network in the CCA, the cross-linking agent as used in this step assists formation of the hydrogel and strengthens the resulting hydrogel film so that a self- supporting film results. Hydrogel films can be formed when as little as 1 part in 100 parts by weight of the monomer mixture is the cross-linking agent. Generally, increasing the amount of crosslinking agent lowers the sensitivity of the gel to the analyte being detected. Preferably, crosslinker is used in an amount between about 4 and 15% of monomer weight, more preferably about 5% of monomer weight.

The gel monomer component of the hydrogels of the present invention can be any compound that forms a hydrogel that undergoes a volume change in response to a stimulus or stimuli. Examples of suitable gels include, but are not limited to, acrylamide gels, purified agarose gels, N-vinylpyrolidone gels and methacrylate gels. Preferred gels for use in the present invention are N-isopropylacrylamide (NIP A) and acrylamide.

The phase transition properties of the hydrogel are modified by functionalizing the hydrogel with a reagent that specifically binds an analyte of interest.

Thus the gel is modified so as to detect the presence of a stimulus by means of this molecular recognition component. More specifically, a monomer capable of selectively interacting with a specific solute is incorporated in the hydrogel. Typically, the more of the molecular recognition component, the more sensitive the device to the desired analyte. This relationship, however, is generally only observed up to a certain concentration of the molecular recognition component, after which the sensitivity of the gel decreases. Any monomer having molecular recognition capabilities for the desired solute can be used.

For example, 4-acrylamidobenzo 18-crown-6 ether, which selectively binds Group I cations and preferably binds potassium ions, can be used if potassium is the analyte of interest. Other crown ethers, cyclodextrans, caloxarenes, and other chelating agents can also be used.

When the analyte binds to the gel matrix, it causes a change in the hydrophilicity of the matrix, and therefore changes the swelling properties of the gel. As the hydrogel shrinks and swells, the CCA embedded in the hydrogel follows. As the CCA changes dimension, the resulting diffraction wavelength alteration reports on the array volume change. The diffraction shifts to shorter wavelengths as the gel shrinks, and to longer wavelengths as the gel swells. Measuring this alteration, therefore, allows for detection of the stimulus which caused the volume change.

In addition, a third monomer component can be added to change the sensitivity of the device by making the hydrogel even more hydrophobic or hydrophilic, as desired by the needs of the user. The more hydrophobic the gel, the more it tends to stay in a collapsed or shrunken state. For example, an acrylamide, which is more hydrophilic than NIP A, can be added, or N-butylacrylamide, which is more hydrophobic than NIP A, can be added to adjust the properties of the hydrogel.

As stated above, the devices of the present invention combine CCA technology with modified hydrogels to provide devices useful, for example, as sensor devices. More specifically, a hydrogel having the characteristics described above is polymerized around a fluid CCA.

Changes in the volume of the hydrogel matrix change the lattice spacing of the embedded CCA, thus changing the color of the light diffracted. These devices are well suited for sensor applications due to the unique ability to directly measure the volume change of the hydrogel by monitoring the diffraction wavelength from the CCA. In many applications, the change in color can be detected by the unaided eye. For example, less than a 5% expansion in volume can yield a color change detectable by the unaided eye. By way of nonlimiting example, sensing material in accordance with the invention is shown generally as sensor 700 in FIG. 7A. Sensor 700 includes a plurality of CCA particles 710 in a polymer 720, and includes a plurality of receptor sites 730. In the exemplary embodiment shown in FIG. 7A, receptors 730 are glucose receptors. Referring to FIG. 7B, when sensor 700 is in contact with a solution containing glucose, the receptors will bond to the glucose in proportion to the glucose concentration. Referring to FIG. 7C, this will cause the polymer to expand, which causes a change in the wavelength of diffracted light 740, which causes sensor to appear to be a different color to a viewer 750. For example, if sensor 700 swells, in response to increased glucose concentration, CCA particles 710 will expand and the color of sensor 700 will change from a relatively short wavelength color to a color of longer wavelength.

A method for making sensing material according to the present invention generally comprises the steps of allowing charged particles to self assemble into a crystalline colloidal array; adding a first comonomer that is a gel monomer, a crosslinking agent, a second comonomer that is a molecular recognition monomer to a medium comprising said crystalline colloidal array and a polymerization initiator; and polymerizing the mixture to form a crystalline colloidal array embedded in a hydrogel.

An alternative method for making a device according to the present invention generally comprises the steps of allowing charged particles to self assemble into a crystalline colloidal array; adding a crosslinking agent, a gel monomer, and a polymerization initiator; polymerizing the mixture to form a crystalline colloidal array embedded in a hydrogel; and adding a molecular recognition component capable of binding with the hydrogel. Any suitable particles can be used. For example, the particles used to create the CCA can be colloidal polystyrene, polymethylmethacrylate, silicon dioxide, aluminum oxide, polytetrafluoroethylene or any other suitable materials which are generally uniform in size and surface charge. Colloidal polystyrene is preferred. The particles are chosen depending upon the optimum degree of ordering and the resulting lattice spacing desired for the particular application. The particles preferably have a diameter between about 50 and 500 nanometers and may be either synthesized as discussed below or obtained commercially. Electrically charged particles that can be used in accordance with this embodiment are commercially available from Dow Chemical or Polysciences, Inc.

Monodisperse particle colloids can be prepared by emulsion polymerization or any other means. For example, an emulsion polymer colloid can be prepared by mixing the desired monomer with a cross-linking agent, a surfactant to aid in the formation of the emulsion, a buffer to keep the pH of the solution constant and to prevent particle coagulation, and a free-radical initiator to initiate polymerization. In a preferred embodiment, the monomer is styrene, the cross-linking agent is divinylbenzene, the surfactant is sodium-di(l,3-dimethylbutyl)sulfosuccinate, the initiator is preferably potassium persulfate and an ionic comonomer is also added, preferably 1 -sodium, 1- allyloxy-2-hydroxypropane sulfonate. Other suitable compounds can also be used to prepare the emulsion polymer colloid, so long as compatibility problems do not arise. The particles should then be purified by the use of centrifugation, dialysis and/or an ion exchange resin. Purification of the commercially available particles is also required.

Following polymerization, the particles may be stored in an ion exchange resin, preferably in a bath of 10% by weight suspension of ion exchange resin such as analytical grade AG51X8 mixed bed resin commercially available from Bio-rad of Richmond, Calif. The ion exchange resin should preferably be cleaned prior to use through a suitable procedure such as that of Vanderhoff et al. in the Journal of Colloid and Interface Science, Vol. 28, pp. 336-337 (1968).

The electrically charged particles are then allowed to self assemble to form a crystalline colloidal array. This assembly takes place in a suitable solvent, preferably water. To the CCA medium is then added a gel monomer, a molecular recognition monomer, a cross-linking agent and a polymerization initiator. Any suitable initiator can be used, such as a thermal initiator or a photoinitiator. Preferably, a UV photoinitiator is used. A preferred UV photoinitiator for this use is 2,2'-diethoxyacetophenone. Any cross- linking agent, gel monomer and molecular recognition monomer discussed above can be used.

After formation, the mixture is then polymerized. Any means known in the art can be used to initiate polymerization, so long as the method for polymerization does not destroy or otherwise disorder the CCA. Preferably, the polymerization is accomplished by placing the mixture between two plates, preferably quartz plates separated by a parafilm spacer, at a temperature from between about 0° to 10° C. The plates are then exposed to UV light. Exposure to the UV light effects complete polymerization after about 5 minutes. Upon completion of the polymerization, the plates are removed and a stable polymerized CCA (PCCA) results. This film can be approximately about 150 microns thick and can be made thinner based upon the needs of the user. In a preferred embodiment, the hydrogel is composed of a copolymer of NIPA and 4-acrylamidobenzo 18-crown-6 ether crosslinked with N,N'- methylenebisacrylamide as shown in FIG. 3. The crown ether in the hydrogel complexes with metal cations, with an affinity that depends both on the ability of the cation to fit into the cavity of the crown ether, and the charge of the ion. The NIPA gel is moderately hydrophilic. The copolymer is highly sensitive to slight changes in its hydrophilicity due the complexation of small amounts of cations. As the crown ether binds with cations, the entire copolymer becomes more hydrophilic causing the PCCA to swell and the diffraction wavelength to increase. The linear NIP A/crown ether copolymer is only moderately hydrophilic and precipitates out of solution above about 38°C. At 23°C, however, the polymer-solvent attraction is only slightly greater than the polymer-polymer attraction in the hydrogel.

Sensing material of this embodiment is particularly useful as a sensor for lead. The material swells in lead concentrations between about 2 μM and about 10 mM. This detector functions as an easy to use, sensitive detector which is blue at lead concentrations of about 2 μM or less and green at concentrations of about 20 μM. The color change of the sensing material can be detected by the unaided human eye at lead concentrations of approximately 15 μM, and can be detected by spectrophotometry at even lower concentrations. At concentrations higher than about 20 mM, the sensing material shrinks and the wavelength diffracted gets smaller. The sensor is reversible and the diffraction reverts to its original wavelength when the lead is allowed to exchange out. For example, the PCCA completely returns to about its original volume and diffraction wavelength after soaking for a few minutes in deionized water. Diffraction peak maxima of the PCCA are reproducible to within 1 nm after successive washings and reimmersion in lead solutions, at a constant temperature of 23°C. Similar lead sensors can be fabricated using acrylamides that do not have a volume temperature dependence.

In addition, sensing material in accordance with preferred embodiments of the invention can selectively bind group I cations, in one embodiment, binding potassium over sodium, for example. The PCCA swells in potassium chloride (KCl) solutions at concentrations ranging from 1 to 20 mM at 23°C. and the gel begins to contract at higher KCl concentrations. Sodium ions, which have a lower affinity for the crown ether group, have little effect on the diffraction below approximately 20 mM. The maximum diffraction wavelength shift from pure water to 100 mM sodium ions is only about 15 nm whereas the maximum diffraction wavelength shift from pure water to 20 mM potassium ions is about 100 nm. The sensing material is sensitive to concentrations of potassium ions less than 1 mM; the diffraction wavelength of the PCCA shifts 25 nm between the pure water and 1 mM KCl, which shift can be seen by the unaided human eye. Thus, the sensor functions as a sensitive and easy to use detector for potassium as well as lead, with a 500 fold greater affinity for lead than potassium.

Alternatively, the incorporation of other crown ethers in the hydrogel could produce a sensor that selects other cations. The selectivity of the sensor is limited by non- selective binding of the crown ether with other cations. Similarly, use of functionalized compounds other than crown ethers, such as cyclodextrans, caloxarenes or other chelating agents, can produce devices that respond to still other stimuli.

The response rate of the PCCA described above as the preferred embodiment, having a thickness of about 150 microns, is typically less than about 5 minutes. Response rate can be improved by decreasing the thickness of the PCCA. The response rate is partially determined by the mass transport of cations into the gel, and partially determined by the kinetics of complexation. Decreasing the gel thickness and the monomer content of the gel will markedly increase the rate of analyte mass transport to the active sites on the gel, and therefore decrease response time. Response rate will also be effected by the molecular recognition component used, as some will be more selective than others. Response rates of between about 1 and 5 minutes can be achieved with a 150 micrometer thick gel and response rates on the order of seconds can be achieved with thinner gels. The response rate is inversely proportional, to the thickness of the gel.

In addition, the present invention contemplates embodiments in which the gel monomer will change volume in response to temperature changes. For example, NIPA hydrogels change volume with changes in temperature. Temperature has a large effect on the diffraction of the sensor in a particular concentration of KCl. The diffraction wavelength of the sensor in 5 mM KCl is 595 nm at 23°C, but increases to 710 nm at 7°C, and decreases to 495 nm at 32°C. Thus, if using a hydrogel that is also responsive to temperature, the sensor should be maintained at a constant temperature during use.

In another embodiment of the present invention, the hydrogel in which the CCA is polymerized comprises a crosslinking agent, a gel monomer and a biomolecular recognition component. This biomolecular recognition component is a biomolecule that selectively binds a specific chemical specie as part of its biological function. This component can be bound to the gel directly or by one or more linking molecules. Examples of such biomolecular recognition components include but are not limited to enzymes, antibodies, antigens, porphyrins, ferritin, or pheromone receptors. These natural recognition components can respond to simple chemical species, or to the presence of particular proteins.

These sensor devices can therefore further comprise one or more linking molecules that bind the biomolecular recognition component to the gel monomer. In addition, the biomolecular recognition component can be modified by being reacted with a molecule that can be bound to the linking agent, or to the gel itself. A particularly advantageous linking molecule is 5-(biotinamido)pentylamine, and an advantageous molecule for reaction with the biomolecular recognition component is avidin. Avidin is a protein extracted from egg whites and has four binding sites for biotin.

Sensors of this embodiment have particular application in the area of detection of disease markers, for example in detecting the presence of HIV antibodies. The gel can be sensitive to very low concentrations of species, if the recognition element has a high binding constant. This is attributable to the fact that the PCCA recognition element concentrates the analyte within the PCCA.

For example, an antigen can be added to a gel monomer to form a hydrogel that binds such things as antibodies to tuberculosis cells, cancer cells, or HIV. The antigen is chosen based on what medical condition is to be detected. Enzymes can also be attached to the gel for medical diagnostics. For example, binding glucose oxidase to the hydrogel will allow for the detection of glucose. Thus this embodiment of the present invention has application as a medical diagnostic tool. As discussed above, the sensitivity of the sensor can be adjusted to the desired concentration by modifying the ratio of gel monomer to recognition component, the degree of crosslinking and the hydrophobicity of the gel monomer. Hydrophobicity can be adjusted as discussed above with the addition of another monomer that is either more or less hydrophobic than the gel monomer, depending on the needs of the user.

The antibody and antigen based sensors function much the same way as the chemical sensors discussed above. That is, the gel volume changes when the gel becomes bound to a chemical specie that changes the hydrophobicity of the gel.

In the case of the enzyme based sensors, the enzyme changes the chemical nature of the analyte by first binding to the analyte substrate and then cleaving or otherwise reacting with the analyte substrate. The gel of the enzyme based sensors swells because the interior of the gel has a high concentration of reaction products and a low concentration of analyte substrate, while the liquid surrounding the gel has the opposite characteristics. This causes an osmotic pressure imbalance between the inside and outside of the gel. A solvent, preferably water, diffuses into the gel to relieve that pressure imbalance; it is this excess solvent that causes the gel to swell. If immersed in a fresh solution of the substrate, the sensor will expand again. The response of the sensor, therefore, is dependent upon the concentration and amount of substrate in its immediate environment.

Sensors in accordance with the invention can be made by polymerizing a CCA in a hydrogel comprising a crosslinking agent and a gel monomer such as those described above. Following formation of the PCCA, a molecular recognition component is added. In an advantageous embodiment, addition of the molecular recognition component is accomplished by first hydrolyzing the PCCA. Any means known in the art can be used to effect hydrolysis. An advantageous method is to place the PCCA in a 0.1M solution of sodium hydroxide for about 10 minutes. Hydrolysis of the PCCA serves to establish acidic, reactive sites on the PCCA matrix. Preferably, the hydrolysis is a partial hydrolysis in which 10 to 30% of the reactive sites on the PCCA matrix have been acidified. This is accomplished by hydrolyzing for about 10 minutes.

The acidified PCCA is then reacted with a linking molecule and a coupling agent that binds the compound in place of the acid groups on the matrix. One linking molecule is a 5-(biotinamido)pentylamine and a suitable coupling agent is l-(3- dimethylaminopropyl)-3-ethylcarbodiimide. Other compounds and water soluble coupling agents can also be used. As will be appreciated by one skilled in the art, the reaction can be performed without a coupling agent, but would proceed more slowly if one is not used.

The PCCA should be reacted with the linking molecule for a period of time sufficient to effect reaction of all of the acid; when using a coupling agent this is typically between about 3 to 6 hours.

A molecular recognition component, such as an enzyme, antibody or antigen, is then added, and binds to the compound. The molecular recognition component is first bound to a compound having an affinity for the linking molecule. A compound for this use is avidin, which is preferred when using biotin as the linking molecule. Thus, the enzyme is bound to the PCCA without destroying the CCA structure or the reactivity of the enzyme.

In principle, any biomolecule that can be avidinated can be incorporated onto the PCCA according to this embodiment of the present invention. For example, recognition elements such as antigens that bind HIV antibodies can be attached to the

PCCA to create clinical diagnostic sensors. The sensitivity and useful dynamic range of the PCCA sensors can be simply adjusted by changing the gel monomer-recognition element concentration ratio, as well as altering the degree of hydrogel crosslinking.

The enzymes bound to the PCCA then react with a specific compound. For example, if glucose oxidase is used as the enzyme, the gel will cleave glucose, and if β-D- galactosidase is used as the enzyme the gel will cleave β-D-galactose. Reaction of the sensors with the specific compound causes the PCCA diffracted wavelength to shift. For example, exposure of a glucose oxidase labeled PCCA to glucose causes the hydrogel to swell, which shifts the PCCA diffracted wavelength towards the red end of the spectrum. The glucose sensor PCCA swells in glucose concentrations of between about 0.1 mM and 0.5 mM solutions. The sensor swelling saturates above about 2 mM glucose due to formation of a steady state for the glucose oxidase conversion of glucose to gluconic acid and for the reoxidation of the enzyme by dissolved oxygen. The glucose sensor returns to its original volume and diffraction wavelength after removal from the glucose solution. The glucose oxidase enzyme remains biologically active for at least about four months.

The swelling of the enzyme sensor appears to be due to formation of an anionic reduced flavin in the glucose oxidase enzyme upon glucose turnover, although the inventors do not wish to be bound by this mechanism. The oxidized form of the enzyme is uncharged at neutral pH. The reduced flavin prosthetic group, however, is anionic at neutral pH. The resulting electrostatic repulsion between reduced flavin moieties causes the gel to swell. The reduced form of the enzyme is reoxidized by 0₂ in the solution:

E+Glucose->EH₂ ^1_ + Gluconic Acid EH₂ ^1~ + 0₂ → H₂0₂+E The electrostatic nature of the gel swelling can be confirmed by addition of salts such as NaCl in a concentration of about 0.2 mM, which screen the electrostatic interactions.

As will be appreciated by those skilled in the art, the biomolecular recognition component can be added in numerous ways. In a preferred embodiment described above, this addition is effected by reacting the biomolecular recognition component with avidin, which binds to the 5-(biotinamido)pentylamino bound to the gel matrix. This method, therefore, essentially uses two linking molecules. Embodiments using only one linking molecule or more than two linking molecule, or use of no linking molecule at all, are also within the scope of the invention.

One application of the sensors discussed herein is direct use or incorporation in or on a 1 or 2 layer biocompatible carrier and use as an implant placed directly under the skin. The device would detect a specific chemical stimulus in the body and undergo a volume change in response thereto. As a result of the volume change, the lattice structure of the CCA, and therefore the diffracted wavelength of the CCA, would also change. This wavelength change could be detected through the skin. Alternatively, a system including the sensor diffracted in the infrared range could be placed more deeply under the skin, such that the wavelength change would not be detectable unless an IR light source and a spectrometer was used.

Another particularly preferred application for the diagnostic systems of the invention is to determine the concentration of a particular analyte as present in tear fluid. In this embodiment of the invention, the sensing material can be used alone or incorporated in or on a 1 or 2 layer carrier. The carrier or sensing material only, can be constructed to rest under the eyelid, preferably under the lower eyelid. The sensing material can be viewed by retracting the lower eyelid. In another embodiment, the carrier can be formed similar to a contact lens, and could contain sensor material as described herein for determining the concentration of various analytes in the tear fluid, for example, the glucose level in the tear fluid. Such sensing material is preferably incorporated at or near the rim of the lens, so as not to interfere with the vision of the user.

In another embodiment of the invention, the sensing material is constructed so as not to be noticeable when illuminated with ordinary light, but which will be noticeable and exhibit noticeable color change when illuminated with columnated light.

As discussed below, many substances found in the blood are also found in the tears and the concentration of the substances in the tears will vary in proportion to the change of concentration of the substance in the blood. The following materials have been found in tear fluid as is discussed in "Clinical Biochemistry of Tears", N.J. Haerington, Survey of Opthamology, 26:2 (1981), incorporated hereby by reference, proteins, enzymes, lipids, metabolites, electrolytes, hydrogen ions, and drugs. More specific examples of proteins include tear albumin, lactoferrin, transferrin, lysozyme, Immunoglobulin A, G and E (InA, InG, InE), glycoproteins, and antiproteinases. Enzymes include glycolytic enzymes, enzymes of the tricarboxylic acid (Krebs) cycle, LDH, lysosomal enzymes, β-Hexosaminidase, α-Galactosidase, β-Galactosidase, - Fucosidase, α-Mannosidase, α-Iduronidase, Sulfatase A and B, amylase, peroxidase, plasminogen activator, and collagenase. Lipids include cholesterol, triglycerides, diglycerides and monoglycerides. Metabolites include glucose, urea, catecholamines, histamine and prostaglandin. Electrolytes include sodium, potassium, calcium and magnesium. Evidence of drug use can also be monitored through analyzing teat fluid. Tear fluid has been found to contain phenobarbital, carbamazepine, and amphicillin. Accordingly, diagnostic systems in accordance with the invention can be used as both monitoring systems and screening systems for the above substances and others. For example, systems in accordance with the invention can be inserted on the eye and used to screen for the presence of diseases or conditions characterized by certain substances in the tears.

Carriers for the sensing device can be single layer, with the sensing material affixed thereto or in a sandwich construction with the sensing material between two layers of carrier material. Alternatively, the sensing material can be used without a carrier, but can be in the same size, shape and location as the carriers discussed below.

Methods of using the above sensing material for detecting the concentration of a selected chemical specie are also provided. Following polymerization of the CCA in the hydrogel, these methods of use further include the steps of measuring the diffracted wavelength of said crystalline colloidal array polymerized in said hydrogel; contacting said polymerized crystalline colloidal array with said solution; measuring the diffracted wavelength of said crystalline colloidal array following exposure to said solution; and comparing the change in diffracted wavelength to determine concentration of said chemical specie.

As discussed above, when a stimulus, such as a chemical specie, becomes bound to said hydrogel, thereby causing the volume of the hydrogel to change, the lattice spacing of the CCA also changes. Accordingly, the diffracted wavelength of the CCA changes as the volume of the hydrogel changes. By determining the change in diffracted wavelength, the volume change of the hydrogel, and therefore the concentration of the chemical specie, can be determined. The higher the concentration of the chemical specie, the greater the swelling (or in certain instances, the shrinking) volume of the gel.

The change in diffracted wavelength can be determined by using instrumentation, such as a spectrometer or a spectrophotometer. In many cases, the diffracted wavelength change can also be seen by the unassisted human eye because the device will change color. By correlating color changes to known concentrations, the color change can be used to determine the concentrations of the stimulus in unknown solutions.

The present invention is also directed to sensors that do not utilize electrostatic interactions for volume changes, but instead utilize the non-ionic volume phase transition phenomenology of NIPA-like hydrogels. The volume phase transition temperature would shift as analytes bound to the recognition elements and the volume would change to alter the diffracted wavelength.

The following examples of sensing material are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1

Charged polystyrene particles are formed by placing approximately 50 g of polystyrene and about 4 g of 1 -sodium, l-allyloxy-2-hydroxypropane sulfonate into about 100 g of water. About 4 g of sodium-di(l,3-dimethylbutyl)sulfosuccinate, about 0.1 g of buffer and about 0.5 g of sodium persulfate dissolved in about 3 ml of water are also added. The mixture is reacted for about 3.5 hours in a flask equipped with a stirring mechanism set at about 355 rpm. The particles are about 105 nm in diameter and are purified by dialysis and ion exchange.

A portion of the colloid suspension is removed and further dialyzed for about one week in deionized water. The solution is then diluted about three-fold, and further purified by shaking with ion exchange resin until all of the impurity ions are removed and the CCA self assembled.

A PCCA is then made by adding to 3 ml of the CCA medium to a mixture comprised of about 0.15 g NIPA, about 0.07 g of 4-acrylamidobenzo 18-crown-6 ether, , about 0.014 g of N.N'-methylenebisacrylamide and about 0.01 g of diethoxyacetophenone. The CCA is allowed to self assemble and the CCA/gel mixture is placed between two quartz plates. The plates are then exposed to UV light for about 5 minutes. The temperature is maintained at about 5°C. throughout.

Example 2

A PCCA sensor made according to Example 1 is tested in potassium chloride (KCl) concentrations ranging from 1 mM to 20 mM at 23 °C. As the crown ether complexes potassium cations, the gel volume increases. The response to KCl is non-linear as can be seen from the extinction spectra of the PCCA sensor in KCl solutions of varying concentration, as is illustrated in FIG. 2 of 5,854,078. At KCl concentrations above 20 mM, the PCCA begins to shrink, as is shown in FIG. 3 of 5,854,078. The sensor returns to its original diffraction color when removed from the KCl solution and id immersed in a deionized water bath for 30 minutes. Example 3

The affinity of the PCCA described in Example 1 for both potassium and sodium can be studied. Although the binding constants of 18-crown-6 type cyclic ethers are highest for potassium, these crown ethers still complex other cations.

The maximum diffraction wavelength shift of the sensor in the presence of

NaCl is 27 nm, which occurs at 100 mM NaCl. The sensitivity to NaCl is significantly lower than the response to KCl, which induced a 100 nm shift at 20 mM KCl. Calcium, although slightly smaller than sodium, causes a diffraction wavelength red shift of only 25 nm at 200 mM. The maximum response of the sensor to NaCl and CaCl₂ occurred at much higher concentrations than the maximum response to KCl. The diffraction wavelength shift of the sensor in KCl, NaCl and CaCl₂ solutions is depicted in FIG. 4 of 5,854,078.

This example illustrates that sodium ions do compete with potassium ions for crown ether binding sites. In 5 mM of KCl, the diffraction wavelength shifts by 90 nm from the diffraction wavelength in pure water. When immersed in a solution of 5 mM NaCl and 5 mM KCl (10 mM total salt), the diffraction wavelength shifts from the value in water by 75 nm. When the 5 mM KCl solution also contained 100 mM NaCl, the diffraction shift is only 55 nm. The diffraction wavelength in the 100 mM NaCl/5 mM KCl solution indicates a KCl concentration of approximately 1.3 mM, based on the calibration curve shown in FIG. 4 of 5,854,078. Example 4

The response of the PCCA described in Example 1 to very low concentrations of lead II acetate can be determined. The sensor has a response, detectable in the spectrometer, of a 10 nm shift in response to a 2 μM (approximately 410 ppb) concentration of lead II acetate. The response of 28 nm to 20 μM (about 4.1 ppm) lead II acetate is easily detectable with the unaided human eye. The device is blue at lead concentrations of 2 μM and green at lead concentrations of 20 μM. The lead response reached a maximum between 10 and 20 mM; the diffraction in 20 mM lead acetate is at a lower wavelength than the diffraction in 10 mM of lead to acetate. The shift in the PCCAs diffraction due the entire detectable concentration range of lead is shown in FIG. 5 of 5,854,078. The sensor returns to its original diffraction color when removed from the lead II acetate solution and immersed in a deionized water bath for 30 minutes. Due to the electrostatic character of the crown ether and cation interaction, this PCCA is found to be about 500 times more effective as a sensor for lead ions than for potassium ions. This sensor, therefore, functions as an effective lead detector.

Example 5

A sensing device can made by taking a blue diffracting suspension of polystyrene colloids prepared as described above in Example 1 and polymerizing a CCA of these colloids in an acrylamide gel. The PCCA is then immersed in a 0.1M sodium hydroxide bath for about 10 minutes, which hydrolyzes some, but not all, of the CONH₂ groups to COOH. The hydrolyzed gel is washed in pure water to remove the sodium hydroxide. At this point, the hydrolyzed gel is swollen and diffracts in the red or infrared region. About 50 mg of 5-(biotinamido)pentylamine and about 100 mg of I-(3- dimethylaminopropyl)-3-ethyl carbodiimide are dissolved in about 1.5 ml of water. The PCCA is immersed in this solution for about 8 hours. Following this period, the reaction products are washed out of the biotinylated gel with distilled water. The spectrum of the PCCA is measured to ensure that the diffraction wavelength is at or near the original blue. About 1 mg of an avidin labelled enzyme is then dissolved in about 1 ml of water; the biotinylated gel is immersed in this solution for between about 3 and 6 hours.

Example 6

The sensor device made according to Example 5, using β-D-galactosidase as the enzyme, is tested in various solutions of o-nitrophenyl-β-D-galactopyranoside ranging from 0.10 mM to 0.33 mM; water and sucrose were used as controls. As can be seen in FIG. 6 of 5,854,078, the wavelength diffracted in the water control is about 505 nm, in a 0.1 mM o-nitrophenyl-β-D-galactopyranoside solution is about 515 nm, in a 0.25 mM solution is about 525 and in a 0.33 mM solution is about 550; the change from 505 nm to 550 nm corresponds with a color shift from green to yellowish green at normal incidence. Diffracted wavelength is determined using a Perkin Elmer Lambda-9 spectrometer. These wavelength shifts demonstrate that the sensor devices of the present invention can be used to detect even small increases in sugar concentration. The sensor gives no response in either 0.1 or 0.2 mM of sucrose, thereby confirming that the enzyme specific reaction between o-nitrophenyl-β-D-galactopyranoside and β-D-galactosidase causes the sensor response. Example 7

The sensor device made according to Example 5, using glucose oxidase as the enzyme, can be tested for reaction with various glucose-containing solutions. As can be seen in FIG. 7 of 5,854,078, the diffraction wavelength when the device is in water is approximately 550 nm. The diffracted wavelength, as measured by a Perkin Elmer Lambda-9 spectrometer, shifts to about 600 nm in a solution of 0.1 mM glucose, and to about 650 in the 0.2 mM through 0.5 mM solutions of glucose. Cleavage of the glucose by the glucose oxidase, when concentrations are at least 0.2 mM glucose, causes a wavelength shift of almost 100 nm, which corresponds to a color shift from yellowish green to deep red at normal incidence and is easily seen with the unaided human eye.

Example 8

The response of the PCCA prepared as described in Example 1 to various lead concentrations can be tested. Diffracted wavelength is determined using a Perkin Elmer Lambda-9 spectrometer. Water is used as a control. Crown ether binding of the lead ions localized the ion charges at the covalently bound crown ether groups. The resulting repulsive interactions cause the gel to swell, which in turn increases the diffracted wavelength. This can be seen in FIG. 8 of 5,854,078.

Example 9

A sensor device can be made according to the methods of Example 5, using glucose oxidase (GOx) as the enzyme. The glucose concentration is kept constant, at a volume of about 0.2 mM, to test the effects of dissolved oxygen on the PCCA. The results are presented in FIG. 9 of 5,854,078, which show the dissolved oxygen dependence of the diffraction wavelength of the film. Diffracted wavelength is determined using a Perkin Elmer Lambda-9 spectrometer. The PCCA is sensitive to oxygen levels between approximately 1.5 ppm and 6.0 ppm. Reoxidation of the flavin was believed to result in a shrinkage of the film, due to the reduction of electrostatic repulsion. This demonstrates that the swelling of the glucose sensor is due to the anionic reduced form of the enzyme as well as demonstrating the utility of the PCCA sensor for detection of gases in solution.

Carriers in accordance with preferred embodiments of the invention are described in U.S. Patent 4,186,184, the contents of which are incorporated herein by reference. Ocular systems are also described in U.S. Pat. Nos. 3,416,530; 3,618,304; and 3,828,777, the contents of which are incorporated herein by the reference. Alternatively, the sensor can be used in the locations, sizes and shapes discussed therein without the use of a carrier.

One embodiment of a sensor system worn on the eye in accordance with preferred embodiments of the invention, is shown generally in cross section in FIG. 4 as sensor system 400. System 400 is preferably similar in size and location to an ocular therapeutic system manufactured for administering a drug to a particular drug tissue site of the eye. However, rather than containing a drug, system 400 contains sensor material, such as the sensor material described above.

Sensors in accordance with the invention are preferably manufactured as a thin sheet, sized, shaped and adapted for insertion and comfortable placement in the eye. The marginal outline of sensor system 400 can be generally ellipsoid, doughnut, bean, banana, circular, ring, crescent, rectangular, square, oval, tombstone, half-circle,- and like geometric shapes. In cross-section, system 400 can be convex, doubly convex, concavo- convex, rectangular and the like. When in the eye, system 400 should be made to adapt the curvature of the part of the eye adjacent thereto, and system 400 should impart its shape to tear film present between system 400 and portion of the eye below the iris.

The dimensions of the ocular system can vary widely. The lower limit on the size of system 400 is the smallest sized system that can be conveniently inserted and maintained in the eye. The upper limit on the size of system 400 is governed by the geometric space limitations of the eye, and comfortable insertion and retention in the eye. Satisfactory results can be obtained with ocular systems for insertion in the cul-de-sac of the eye of an adult human having a length of 2 to 20 millimeters, a width of 1 to 15 millimeters, and a thickness of 0.1 to 4 millimeters. Sensor system 400 is advantageously made of flexible materials that are bio-compatible, non-allergenic to the eye and sized, shaped and adapted for insertion and comfortable placement in the eye of animals, including warm blooded mammals and humans. In a presently preferred embodiment, system 400 is designed for placement in the upper or lower cul-de-sac as seen in FIGS. 5 and 6. The shape depicted in FIGS. 5 and 6, discussed below, will referred to as a banana shape.

System 400, as illustrated in FIG. 4, is shaped in the form of a rectangular ocular device comprising a module 411, having a tear permeable portal layer 412 and other membranes 414 that can be substantially impermeable to the passage of tears. Alternatively, all walls can be formed of tear permeable material. Portal 412 and membrane 414 surround a reservoir 415 containing sensor material 413. In operation, when system 400 is in the eye with portal 412 facing the eyeball, sensor 413 is adjacent the thin eye fluid film positioned between portal 412 and the eye. Alternatively, system 400 can be formed as a pouch with two layers adhered at their periphery, with the sensor material therebetween. In another alternative embodiment of the invention, system 400 can include a layer of sensor material between two tear permeable layers that are not sealed at their edges.

Referring to FIG. 5, ocular diagnostic system 510, in accordance with a preferred embodiment of the invention, is shown positioned in immediate contact with an eye 20. Eye 20 comprises an upper eyelid 21 with eyelashes 22 at the edge of eyelid 21 and a lower eyelid 23 with eyelashes 24 at the edge of eyelid 23. Eye 20 anatomically comprises an eyeball 25 covered for the greater part of its posterior area by a sclera 26 and at its central area by cornea 27. Eyelids 21 and 23 are lined with an epithelial membrane or palpebral conjunctiva, not shown in FIG. 5, and sclera 26 is lined with a bulbar conjunctiva, not shown in FIG. 5. The portion of the palpebral conjunctiva which lines upper eyelid 21 and the underlying portion of the bulbar conjunctiva define as upper cul-de-sac, not seen in FIG. 5, while that portion of the palpebral conjunctiva which lines the lower eyelid 23 and the underlying portion of the bulbar conjunctiva define a lower cul-de-sac, not seen in FIG. 5. System 510 may be shaped and sized for insertion and placement in any part of the eye and in a presently preferred embodiment, system 510 is sized, shaped and adapted for insertion in the lower cul-de-sac. In FIG. 5, system 10 is seen in broken continuous lines in the lower cul-de-sac, generally held in position by the natural pressure of the eyelid.

In FIG. 6, eye 20 is shown in side view in a horizontal section. Eye 20 of FIG. 6 is comprised of an upper eyelid 21 with eyelashes 22, upper cul-de-sac 28, iris 31, cornea 27, tear film 29, aqueous humor 30, lens 32, ciliary muscle 33, lower eyelid 23, lower eyelashes 24, lower cul-de-sac 34 having a palpebral conjunctiva 35 and a bulbar conjunctiva 36 with each able to act as drug receptor tissue sites for specific drugs. System 510 is seen positioned in lower cul-de-sac 34 for continuous monitoring of the level of a substance in the tears.

Materials suitable for fabricating a carrier for holding sensor material against the eye can be selected for diffusional systems from naturally occurring and synthetic materials that are biologically compatible with the eye, its fluid, and eye tissues, and they are essentially insoluble in eye fluids with which the materials will come in contact. Suitable materials include homogenous materials permeable to the passage of tears. Exemplary suitable materials for the fabrication purposes include ethylene-vinyl ester copolymers of the general formula:

wherein R is hydrogen, lower alkyl of 1 to 7 carbons and aryl, and m is (4 to 80)% by weight and n is (100 - m)% by weight. Typical alkyl groups include methyl, ethyl, propyl, isopropyl, tert-butyl, pentyl and hexyl. Typical aryl groups include phenyl. Representative ethylene-vinyl ester copolymers, named as the acetates, include ethylene- vinyl formate, ethylene-vinyl acetate, ethylene-vinyl methylacetate, ethylene-vinyl ethylacetate, ethylene-vinyl propylacetate and the like. A preferred ethylene-vinyl ester copolymer includes ethylene-vinyl acetate having a vinyl acetate content of about 4 to 80% by weight of the total, a melt index of about 0.1 to 1000 grams per ten minutes, a density of 0.920 to 1.09, and a frequency of acetoxy groups on the polyethylene backbone of 1/150 to 1/3.5.

Suitable Ethylene-vinyl ester copolymers including ethylene-vinyl acetate copolymers are disclosed in United States Patent Nos. 4,057,619 and 4,052,505, incorporated by reference. Ethylene-vinyl ester copolymers are commercially available and are described in U.S. Pat. Nos. 2,200,429; 2,396,785 and 2,947,735; and British Pat. Nos. 569,927 and 582,093; and in Crystalline Olefin Polymers, edited by Raff, R. A. V. and Doak, D. W., Part II, pages 261 to 266, 1964, published by Interscience Publishers, New York, all incorporated by reference. Exemplary materials suitable for manufacturing the system include poly(methylmethacrylate), poly(butylmethacrylate), plasticized poly(vinylchloride), plasticized poly(amides), plasticized soft nylon, plasticized poly(ethylene terephthalate), poly(isoprene), poly(isobutylene), poly(butadiene), poly(ethylene), poly(tetrafluoroethylene), poly(vinylidene chloride), poly(acrylonitrile), cross-linked poly(vinylpyrrolidone), poly(trifluorochloroethylene), chlorinated poly(ethylene), poly(4,4'-isopropylidene diphenyl carbonate), plasticized ethylene-vinyl acetate copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-diethyl fumerate copolymer, poly(dimethylsiloxane), ethylene-propylene copolymer, silicone- carbonate copolymers, vinylidene chloride-vinyl chloride copolymers, vinyl chloride- acrylonitrile copolymers, vinylidene chloride-acrylonitrile copolymers, and the like.

Microporous materials suitable for fabricating the carrier for the sensor material include polymers having a pore size of several angstroms, usually at least 10 A to several hundred microns. The porosity of these materials can range from about 5% to about 95%. Exemplary microporous materials include cellulose, acylated cellulose, esterified cellulose, cellulose acetate propionate, cellulose acetate diethyl aminoacetate, poly(urethane), poly(carbonate), microporous polymers formed by the coprecipitation of a polycation and a polyanion as disclosed in -U.S. Pat. Nos. 3,276,589, 3,541,005, 3,541,006, and 3,546,142 (incorporated by reference); modified insoluble collagen, cross- linked poly(vinyl alcohol) with a pore size of 7 A to 50 A, poly(olefins) or poly(vinyl chlorides) with a pore size of about 50 A or less to 150 microns or larger. Also, the materials that can be used include those materials having homogenous properties and microporous properties, such as cross-linked gelatinous membranes.

The amount of sensor material contained in an ocular diagnostic system in accordance with the invention is determined by that amount sufficient to be easily visible, but not so much as to be uncomfortable. Typically, from 25 micrograms or less to about 2000 milligrams or more can be incorporated.

When the diagnostic system is a sealed container with a membrane of a polymer or copolymer and the sensor is in an interior reservoir, the container can be fabricated in many ways. Preformed hollow shapes of polymer or copolymer such as tubing, can be filled with the sensor, and the ends sealed with plugs or by heat to form a system that is partially coated (or uncoated) with an impermeable material. Alternatively, the sensor can be laminated between sheets of the polymer or copolymer which can be sealed together with adhesive or by heat, wherein one or both sheets are formed of a material permeable to tears. Other encapsulation, bonding and coating techniques conventionally used in the art can be employed. Other standard procedures, as described in Modern Plastics Encyclopedia, Volume 46, pages 62 to 70, 1969, published by McGraw Hill, Inc., incorporated by reference well known to those skilled in the art can be used to fabricate the diagnostic systems of the invention.

Example 10

A uniform membrane can be formed by dissolving commercially available ethylene-vinyl acetate copolymer having an acetate content of 40% in methylene chloride in a concentration ratio of 20% copolymer to 80% solvent and film casting the solution onto a glass substrate. The solvent is allowed to evaporate at room temperature and the film warm air dried to yield a film about 1.7. ± .0.2 mils thick.

Example 11

A carrier can be formed with a membrane comprising 80% ethylene-vinyl acetate copolymer having an acetyl content of 40% and 20% diethylhexyl phthalate. The releasing surface of the system measured 16.0 mm by 6.75 mm.

Example 12

A microporous cellulose acetate membrane having a porosity of 60%, a pore size of 0.45 microns and a thickness of 4 mils can be used to form a carrier in accordance with the invention. The system can be inserted in the cul-de-sac of the conjunctiva between the sclera of the eyeball and the lower lid, with the microporous membrane oriented towards the internal surface of the eyelid, or on both sides. Example 13

An ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by weight and a melt index of 22 grams per ten minutes can be used as the carrier material. Generally Ellipsoidal ocular systems having a length of 1.3 cm, a width at their widest point of 4 mm, and a thickness of 0.5 mm, are heat stamped from the assemblage. These ocular systems can be inserted and retained in the cul-de-sac of the conjunctiva between the sclera of the eyeball and the lid with the portal oriented towards the globe.

Example 14

Ocular diagnostic systems of elliptical shape can be formed having a length of 4 to 20 millimeters, a width of 1 to 15 millimeters and a thickness of 0.1 to 4 millimeters. A pre-shaped and sized ethylene-vinyl acetate copolymer tube can be formed, the sensor material inserted therein and the opened end adhesively sealed.

Example 15

Swellable polymers, which change their degree of swelling in response to glucose concentration are described in Kikuechi et al., "Glucose-sensing electrode coated with polymer complex gel containing phenylboronic acid," Analytical Chemistry, 68:5 March 1, 1996, p. 823- 28, the contents of which are incorporated herein by reference.

Copolymers containing phenylboronic acid and tertiary amine moieties can be prepared. Such a copolymer can form a stable complex with polyvinyl alcohol (PVA). The polymer-polymer complex changes it degree of swelling with change in glucose concentration in Dulbecco's phosphate buffered saline solution (PBS) at a pH of 7.4. Thus, phenylboronic acid containing polymers can be used as glucose-recognition molecules. Examples of suitable complexes include poly(3-acryalmidophenylboronic acid-co-N-2-vinyl-pyrrolidone). Amino groups can be incorporated into the polymer or in the vicinity of the boronate moiety to stabilize the complex. Glucose oxidase (GOx) molecules are advantageously incorporated in polymers, such as cellulose acetate, PVA, EVAL, polyurethane and the like. However, boronic acid appears to provide advantages when used as a glucose sensing stimulus, because of its complexation properties and GOx is not necessarily needed.

Example 16

Hydrogels which swell in response to glucose concentration are also described in N.F. McCurley "Optical biosensor using a fluorescent, swelling sensing element", Biosenses and Bioelectronics, 9 (1994) 527-533, the contents of which are incorporated herein by reference.

Fluorescent dye, tetramethylrhodamine cadaverine (TMRC) can be modified so that it can be incorporated into a hydrogel during polymerization. A modified dye can be prepared by reacting 5.5 mg of TMRC with 5 μl of acryloyl chloride (AC) in 2 ml of tertrahydrofuran for three hours in the absence of light. The modified dye (TMRC/AC) precipitated out of solution and was collected.

A hydrogel can be prepared by combining 40% acrylamide solution 2%

(PAm) N,N-methylenebisacrylamide solution (BIS) and concentrated dimethylaminethyl methacrylate (DMAEM). Gels with different physical properties can be made by varying the ratio of BIS: PAm and DMAEM. After dioxidation by bubbling with nitrogen, the TMRC/AC dye congregate is added to the polymer solution, followed by 10-20 μl of a 40% potassium persulphate solution to initiate the polymerization. The resulting gels were transparent. Solidified gels can be molded on glass plates.

A hydrogel membrane that will swell in response to glucose is prepared as follows.

A fluorescent transducer, tetramethylrhodamine cadaverine (TMRC), was incorporated into the hydrogel matrix. TMRC is commonly used in modifying the glutamine residues of proteins. It possesses two important characteristics: first, it contains an amine functional group that can be modified so that it becomes covalently bound to the hydrogel during polymerization and second, it has a reduced sensitivity to pH in comparison with other reactive amine dyes such as fluorescein isothiocyanate and rhodamine. The absorbance spectrum of the derivatized TMRC/AC remains essentially unchanged from the underivatized TMRC spectrum, except for a 8 nm red shift to 550 nm. The derivatized dye follows Beer's Law up to a concentration of 0.1 M. At a concentration of 0.01 M the fluorescence of the derivatized dye in solution reached a maximum. The decrease in fluorescence after 0.01 M was probably due to concentration quenching.

The stability of the immobilized fluorophore in the hydrogel is determined by immersing two gels in deionized water for approximately 24 hr. One gel is prepared with the underivatized dye while the other is prepared with the TMRC/AC conjugate.

13% of the TMRC but only 0.5% of the TMRC/AC conjugate leaches from the gel. This suggests that the derivatized dye is covalently bound to the gel matrix. Detection of glucose concentration is based on protonation of the hydrogel, leading to an increase in gel volume. GOx catalyses the oxidation of β-D-glucose to D- gluconic acid and H₂0₂. The gluconic acid then protonates the amine moiety. Hydrogel disks containing covalentaly immobilized TMRC/AC and entrapped GOx and catalase can be placed in glucose solutions ranging in concentration from 0 to 400 mg/dl. The catalase will scavenge the hydrogen peroxide produced by this reaction and catalyze the composition of hydrogen peroxide into water and oxygen to decrease oxygen depletion of the gel caused by glucose oxidase reaction.

By measuring the wavelength (color) change of sensing material in accordance with the invention, when placed in standardized solutions of known concentration of selected substances, standards can be established to correlate a color to a concentration of selected material. Correlating the color of the sensor in use to the concentration of selected substances in blood samples can establish standards so that the sensor can be used to measure blood level concentration. If the sensor is to be placed in the eye, the blood level of the substance be monitored in the body of the sensor nearer should be measured to establish standard correlations between blood levels of a substance and tear levels of that substance.

It will thus be seen that the objects set forth above and those apparent from the preceding description are efficiently attained and that certain changes can be made in carrying out the above methods and products without departing from the spirit and scope of the invention, it is intended that the above descriptions are intended to be illustrative, rather than limiting.

Claims

C L A I M SWhat is claimed is:

1. A system for measuring the concentration of a selected substance in tear fluid, comprising: a layer of sensor material, comprising a hydrogel containing receptor sites which bond to targeted molecules and cause the hydrogel to experience volume variations dependent on the concentration of the targeted molecules in fluids in contact with the sensor, the sensor constructed in a shape and of dimensions to fit between the lower eyelid and the eyeball, below the iris, and the hydrogel is constructed to exhibit perceptible color changes as the hydrogel experiences volume variations in response to changes in concentration of the targeted molecules, said changes in concentration being within ranges which will occur in human tear fluid.

2. The system of claim 1, wherein the detector sites are selected and the hydrogel is constructed to cause the hydrogel to experience perceptible color changes when in the eye of a diabetic, in response to changes in the concentration of glucose which occur in the tears of a diabetic.

3. The system of claim 2, wherein the color changes occur in response to tear glucose levels corresponding to changes in blood glucose levels in between about 40 mg/dl and 360 mg/dl.

4. The system of claim 1, wherein the hydrogel comprises a crystalline colloidal array of particles.

5. The system of claim 1, wherein the colors exhibited during the color changes in the eye of a wearer comprise red, orange and yellow or orange, yellow and green or yellow, green and blue.

6. The system of claim 1, wherein the sensor is mounted on a polymer carrier.

7. The system of claim 6, wherein the carrier comprises two layers, with the sensor material therebetween.

8. The system of claim 6, wherein the carrier comprises ethylene vinyl acetate.

9. The system of claim 2, wherein the sensor material comprises tetramethylrhodamine cadaverine.

10. The system of claim 2, wherein the sensor material comprises boronic acid and derivatives thereof.

11. The system of claim 2, wherein the sensor material comprises tertiary amine moieties.

12. The system of claim 2, wherein the sensor material comprises phenyl boronic acid.

13. The system of claim 12, wherein the sensor material comprises poly

(vinyl) alcohol.

14. The system of claim 1, wherein the sensor has a substantially oval or banana shape.

15. A system for self-monitoring of blood glucose levels, comprising: a mirror having colors thereon and text associated with the colors indicating which colors are indicative of high blood glucose levels, which are indicative with normal blood glucose levels and which are indicative of low blood glucose levels.

16. The system of claim 15, wherein the text associates certain colors on the mirror with blood glucose concentration ranges, including values within at least the range from about 360 mg/dl to 40 mg/dl.

17. The system of claim 15, wherein relatively shorter wavelength colors are associated with relatively lower blood glucose levels than the longer wavelength colors.

18. The system of claim 15, wherein the mirror is coupled to a light source constructed to illuminates the eye area of a user when they look into the mirror.

19. The system of claim 18, wherein the light from the source is monochromatic.

20. The system of claim 18, wherein the light is mounted and the mirror is constructed to illuminate the sensor with light at a substantially fixed angle to the eye and mirror.

21. The system of claim 15, comprising a sensor device worn under the eyelid, which change color in response to changing concentration of a selected substance in the tears of a user.

22. The system of claim 15, wherein the colors are arranged in a full or partial ring.

23. The system of claim 15, wherein relatively longer wavelength colors are associated with relatively lower blood glucose levels than the shorter wavelength colors.

24. A method of self monitoring blood glucose levels, comprising: placing a sensor device under the lower eyelid of a user, the sensor constructed to change color in response to changing levels in tear glucose levels; retracting the lower eyelid to view the sensor while looking into a mirror having colors thereon which match the colors the sensor will turn when exposed to the range of tear glucose levels corresponding to blood glucose levels within the range of about 40 mg/dl to 360 mg/dl; and