WO2003029830A1

WO2003029830A1 - Cleaning method

Info

Publication number: WO2003029830A1
Application number: PCT/GB2002/004441
Authority: WO
Inventors: Stuart Anthony Elmes; Martin Horrod; Ralph Von Strandmann; Anthony Brown
Original assignee: Genomic Solutions Acquisitions Limited
Priority date: 2001-10-03
Filing date: 2002-10-02
Publication date: 2003-04-10

Abstract

A method of operating a liquid transfer device, including the steps of using the liquid transfer device to transfer a first sample to a substrate, cleaning the liquid transfer device to remove any of the first sample left residing on the liquid transfer device, and then using the liquid transfer device to transfer a second sample to a substrate, wherein the step of cleaning the liquid transfer device is carried out by immersing a portion of the liquid transfer device on which the first sample resides in a fluid in whose presence the first sample to be removed from the liquid transfer device exist on the surface as charged species, and creating an electric field within the fluid to attract the first sample away from the liquid transfer device; and a use of the method of claim (2) for performing arraying of biological samples.

Description

CLEANING METHOD

The present invention relates to a method of removing unwanted material from a surface of a component, and particularly to a method of removing unwanted material from a surface of a liquid transfer device for cleaning the device between transfers of different samples.

BACKGROUND OF THE INVENTION

One application in which there is often a need to remove unwanted material from the surface of a component is the micro or macro arraying of biological samples using a reusable liquid transfer device. A liquid transfer device such as a liquid transfer pin or printing head is used to transfer relatively small amounts of samples from a sample source to a substrate to form a micro or macro array. The transfer is typically automated using a robotic system. When the device is used to transfer a plurality of samples, the device is washed/ cleaned between samples. Minimisation of the carryover between samples is considered to be a high priority by researchers in molecular biology, and it is desirable that the process of cleaning the device between samples is as effective as possible in order to reduce carryover and give high quality and accurate results.

It is also desirable that the cleaning process can be carried out as quickly and efficiently as possible to minimise the time taken to complete a printing cycle.

Conventional methods of cleaning liquid transfer/printing devices include the following. According to one method, the working end o the device is immersed in a bath of a cleaning solution and the bath is vibrated at high frequencies to dislodge the unwanted material from the surface of the device. According to another method, the working end of the device is first wetted and then dried using a powerful vacuum system. According to yet another method, the working end of the device is submerged in a bath of cleaning solution, and the device is agitated to encourage the unwanted material to diffuse away from the surface of the device. Each of these conventional methods has its drawbacks, and it is an object of the present invention to provide an alternative method for removing unwanted material from a surface of a component.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method of removing unwanted biological material from a surface of a component, including the steps of: immersing the surface of the component in a fluid in whose presence the biological material exists on the surface as charged species, and creating an electric field within the fluid to attract the biological material away from the surface of the component.

The fluid may for example be water where the unwanted material is a material such as DNA that exists as charged species in the presence of water. For those materials that would exist as neutral species in the presence of water, a different fluid would be used in whose presence the material would exist as charged species such as charged colloidal particles or molecules. For example, an aqueous solution having an increased or reduced pH could be used to provide an environment in which the unwanted material exists on the surface of the component as charged species.

According to another aspect of the present invention, there is provided a method of operating a liquid transfer device, including the steps of: using the liquid transfer device for the transfer of a first sample; cleaning the liquid transfer device to remove any of the first sample left residing on the liquid transfer device, and then using the liquid transfer device for the transfer of a second sample; wherein the step of cleaning the liquid transfer device is carried out by immersing a portion of the liquid transfer device on which the first sample resides in a fluid in whose presence the first sample to be removed from the liquid transfer device exists on the surface as charged species, and creating an electric field within the fluid to attract the first sample away from the liquid transfer device. The liquid transfer device may, for example, be used to transfer samples onto a solid surface or into a liquid.

The electric field may be created by applying a potential difference between the surface of the component and an electrode provided within the fluid. In one embodiment, the surface of the component is placed between two electrodes of opposite polarity for removing both negatively and positively charged species from the surface of the component.

Non-limiting examples of biological materials to which this technique has particular application are peptides, proteins, antibodies and oligonucleotides such as DNA.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described hereunder, by way of example only, with reference to the accompanying drawings, in which: -

Figure 1 shows a schematic view of a system for removing unwanted material from the surface of a component in a method according to a first embodiment of the present invention;

Figure 2 shows a schematic view of a system for removing unwanted material from the surface of a component in a method according to a second embodiment of the present invention;

Figures 3 to 6 show different configurations for the electrodes of the second embodiment for creating an electric field in the fluid; and

Figure 7 are fluorescent images showing the effect of the cleaning technique according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to Figure 1, a system for cleaning a surface of a liquid transfer pin in a method according to a first embodiment of the present invention comprises a vessel 2 containing a fluid 4 into which the surface of the liquid transfer pin 10 to be cleaned is immersed. The fluid is selected such that in the immersed condition the material to be removed exists as charged species on the surface of the component. An electrode 22 is immersed in the fluid 4, and a voltage is applied across the pin and the electrode by means of a DC power supply 12. Charged species on the surface of the liquid transfer pin opposite in polarity to the electrode are attracted away from the surface of the liquid transfer pin and towards the electrode through the fluid by electrophoresis. This embodiment is of particular use where the unwanted material to be removed exists as species of a single polarity, such as a pin from which DNA is to be removed.

The voltage is selected taking into account the increased cleaning effect observed with higher voltages, and higher current densities, and the undesirable side effects of using relatively high voltages, such as the production of hydrogen at the electrodes. Where appropriate, the pin could be cleaned by carrying out a succession of washes at a relatively low voltage.

The system was tested using a liquid transfer pin from which DNA was the material to be removed, and using an aluminium plate as the separate electrode where the spacing between the pin tip to be cleaned and the separate electrode was approximately 1mm. Tris-Borate (TBE) was used as the media for the testing as its high salt content gives it a relatively high conductivity. Electrical connections were made between the liquid transfer pin and the electrode. The liquid transfer pin was submerged in the TBE bath completing an electrical circuit and held there for five seconds. The system was tested with no potential applied between the liquid transfer pin and the electrode (in theory any washing is due to passive diffusion of species off the pin in the TBE bath), with the pin as the cathode and the electrode 22 as the anode (in theory attracting any negatively charged DNA from the surface of the pin), and also with the electrode as the cathode and the pin as the anode of the circuit (in theory preventing diffusion of DNA from the surface of the pin).

The amount of un-labelled DNA remaining on the pin after the five second wash and pin dry was measured by staining any deposited DNA with a fluorescent dye (POPO-3) and assessing the amount of fluorescence from the washed pin using fluorescent imaging equipment. The results of the test are shown by the fluorescent images in Figure 7 of well plates, in which the first row of nine spots are printed using pins loaded with DNA before any wash and the second row of nine spots are printed using pins loaded with DNA and then subjected to a single 5-second wash at different potential differences. As is clear from the images, it was found that the amount of DNA removed in a five second wash was hugely altered by the application or not of a voltage. The results show that the wash with no voltage applied (Figure 7(a)) gave a sample cross-contamination level of 10%. When the pin was made the cathode and 30N applied across the liquid transfer pin/aluminium electrode circuit (current ~ 80mA) (Figure 7(b)) the cross- contamination level dropped to an un-measureable quantity (<< 1%). As a further control test if the liquid transfer pin was made the anode and the same voltage/current applied the cross-contamination level increased to 25% (Figure 7(c)). These results show that the application of an electric field within the fluid so as to attract unwanted charged species on the surface of the pin has a significant cleaning effect beyond that possible by passive diffusion.

Although, in this case a simple setup was used with only one bath at a single polarity it could be imagined that contaminants with both negatively and positively charged species could be removed using either two baths at different polarities or a single bath in which the polarity and conducting media could be changed (this would prevent re-attachment of species already removed when the polarity was changed). Although an aluminium electrode is used in the example described above, electrodes made of noble metals such as platinum would be preferred from the point of view of increasing the lifetime of the electrodes. For example, platinum- coated structures or platinum wires could be used.

With reference to Figure 2, a system for cleaning a surface of a liquid transfer pin in a method according to an alternative embodiment of the present invention comprises a vessel 2 containing a fluid 4 into which the surface of the liquid transfer pin 10 to be cleaned is immersed. The fluid is selected such that in the immersed condition the material to be removed exists as charged species on the surface of the component. An anode and cathode 6, 8 are immersed in the fluid 4, and a voltage is applied across the electrodes by means of a DC power supply 12. The charged species on the surface of the liquid transfer pin are attracted away from the surface of the component and towards either the cathode or the anode depending on the polarity of their charge through the fluid by electrophoresis.

Again, the voltage is selected taking into account the increased cleaning effect observed with higher voltages and higher field strengths, and the undesirable side effects of using relatively high voltages, such as the production of hydrogen at the electrodes. Where appropriate, the pin could be cleaned by carrying out a succession of washes at a relatively low voltage.

A variety of configurations can be adopted for the electrodes. As shown in Figure 3, the electrodes may have a fork configuration, whereby a number of liquid transfer pins can be cleaned simultaneously by placing each pin 10 between a prong of the forked cathode and a prong of the forked anode.

One variation of the forked electrode configuration is shown in Figures 6a and 6b. Although Figure 6a shows a perspective view of only one electrode structure for use in the configuration shown in Figure 3, the opposing electrode structure will have a corresponding construction. Figure 6b shows a cross-sectional view of the electrode structure immersed in the vessel 2 of fluid 4. As shown in Figures 6a and 6b, the electrode structure 6 comprises a support 28 including a number of parallel arms 30. Each arm 30 supports a platinum wire 32, with each platinum wire 32 electrically connected in parallel to a common electrical conductor 34 which is itself connected to the positive or negative terminal of a DC power supply. When the electrode structure shown in Figure 6a is combined with a corresponding electrode structure in the manner shown in Figure 3, the electric field is generated between the platinum wires 32 of the two electrode structures.

As shown in Figure 4, the electrodes could have a tubed configuration, with each electrode being of generally semi-cylindrical shape and joined longitudinally by insulating material 20 to create a tube into which the pin may be inserted.

As shown in Figure 5, two plate electrodes could be arranged in parallel horizontally with the top one of them 6 having a mesh configuration. A plurality of pins could then be inserted through the holes in the mesh such that the surface of each pin to be cleaned resides between the two plate electrodes. The use of horizontal electrodes can give a more concentrated and stronger field around the area to be cleaned.

In the embodiments described above, ddH₂0 could be used as the fluid in the bath because DNA exists as negatively charged species in the presence of ddH 0. However, where the material to be removed would exist as neutral species in ddH₂0, one option would be to use an aqueous solution having a controlled pH under which the material exists as charged species. Controlling the pH of the fluid could also be useful for peptides (proteomics) where a range of charges is likely to occur.

The invention is not limited to the details of the foregoing examples. For example, it is not limited to the use of water or aqueous solutions as the fluid in which the component surface is immersed. Other fluids that support electrophoresis, such as other liquids and gels, may also be used. The electrode arrangements shown in figures 3-6 are shown for the case when the potential difference is applied across separate electrodes with the pin between them and not the case where a potential difference is applied across the pin and an electrode. However, it should be appreciated that corresponding setups could be employed for the case where the pin is used as one of the electrodes. For example, the set-up shown in Figure 2 could be modified by removing one of the fork electrodes, arranging one or more pins in each of the spaces between the prongs, and applying a potential difference across the single fork electrode and pins.

Furthermore, although the present invention has been described in detail with respect to the application of cleaning liquid transfer pins, it is noted that the present invention is not limited to such application and is generally applicable to the removal of biological materials from any component surface.

It is envisaged that the technique described above also has application to the removal from component surfaces of non-biological materials such as organic and inorganic materials in general.

Those skilled in the art would readily appreciate that all parameters listed herein are meant to be exemplary and actual parameters will depend upon the specific application for which the method of the present invention is being used. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only, and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described.

Claims

1. A method of removing unwanted biological material from a surface of a component, including the steps of: immersing the surface of the component in a fluid in whose presence the biological material exists on the surface as charged species, and creating an electric field within the fluid to attract the biological material away from the surface of the component.

2. A method of operating a liquid transfer device, including the steps of: using the liquid transfer device for the transfer of a first sample, cleaning the liquid transfer device to remove any of the first sample left residing on the liquid transfer device, and then using the liquid transfer device for the transfer of a second sample, wherein the step of cleaning the liquid transfer device is carried out by immersing a portion of the liquid transfer device on which the first sample resides in a fluid in whose presence the first sample to be removed from the liquid transfer device exists on the surface as charged species, and creating an electric field within the fluid to attract the first sample away from the liquid transfer device.

3. A use of the method of claim 2 for performing arraying of biological samples.

4. A method according to any one of claims 1 to 3 wherein the electric field is created by applying a potential difference between the surface of the component and an electrode provided within the fluid.

5. A method according to any one of claims 1 to 3 wherein the surface of the component is immersed in the fluid between two electrodes of opposite polarity for removing both negatively and positively charged species from the surface of the component.

6. A method according to claim 5 wherein the surface of the component is positioned between two parallel electrodes of opposite polarity.

7. A method of removing unwanted biological material from a surface of a component substantially as hereinbefore described with reference to any of Figures 1 to 6 of the accompanying drawings.

8. A method of operating a liquid transfer device substantially as hereinbefore described with reference to any of Figures 1 to 6 of the accompanying drawings.