METHOD OF PRINTING A BIOSENSOR PLATFORM

Abstract

The present invention relates to a platform that may be utilised in the field of biosensors. According to the present invention there is a method of manufacturing a platform for use in bio-sensing applications comprising the steps of: a) providing a substrate having electrodes thereon; b) performing an overprinting step by overprinting the electrodes with a precursor solution; c) performing a drying step to dry the precursor solution to form a print layer on the electrodes; d) performing a further overprinting step by overprinting the print layer with a precursor solution to increase the print layer thickness; e) performing a transformation step to at least partially transform the print layer from a first substance to a second substance different to the first substance.

Claims

1. A method of manufacturing a platform for use in bio-sensing applications, comprising: a) providing a substrate having electrodes thereon; b) performing an overprinting step by overprinting the electrodes with a precursor solution; c) performing a drying step to dry the precursor solution to form a print layer on the electrodes; d) performing a further overprinting step by overprinting the print layer with the precursor solution to increase print layer thickness; and e) performing a transformation step to at least partially transform the print layer from a first substance to a second substance different to the first substance.

2. The method according to claim 1, wherein the drying step comprises application of heat.

3. The method according to claim 2 wherein the application of heat comprises heating to a temperature in the range of 50-250° C., for a time period of less than 1 minute.

4. The method according to claim 3, wherein the heating temperature range is between 100-200° C. and the time period is between 20-40 seconds.

5. The method according to claim 1, comprising after step (d) performing further steps of drying the precursor solution and further overprinting with the precursor solution in sequence one or more times to increase the print layer thickness.

6. The method according to claim 1, wherein the transformation step comprises a heat treatment.

7. The method according to claim 6, wherein the heat treatment is for a longer time period at a higher temperature than the drying step.

8. The method according to claim 7, wherein the heat treatment lasts greater than 10 minutes.

9. The method according to claim 8, wherein the heat treatment is at a temperature of greater than 200° C.

10. The method according to claim 1, further comprising a drying step after step d) before the transformation step.

11. The method according to claim 1, wherein the precursor composition is selected to form a solid metal oxide coating during the transformation step.

12. The method according to claim 11, wherein the precursor composition comprises a metal acetate.

13. The method according to claim 1, wherein overprinting is performed by flexographic printing.

14. The method according to claim 1, wherein the electrodes are printed onto the substrate.

15. The method according to claim 1, wherein the precursor solution is overprinted to provide the print layer thickness for each overprinting step of less than 500 nm.

16. A biosensing platform manufactured according to claim 1.

17. The method of manufacturing a biosensor comprising manufacturing a biosensor platform according to claim 1, and functionalising with a biological molecule.

18. The method according to claim 8, wherein the heat treatment lasts approximately 30 minutes.

19. The method according to claim 9, wherein the heat treatment is at a temperature of approximately 300° C.

20. The method according to claim 12, wherein the precursor composition comprises zinc acetate.

Description

[0028] Aspects of the present invention will now be described by way of example only with reference to the accompanying figures in which:

[0029] FIG. 1(a) is a schematic representation of the biosensor with printed ZnO at the interdigitated electrodes on a substrate. FIG. 1(b) shows four biosensors with different number of precursor overprints.

[0030] FIG. 2 is a graphical representation of the thickness of the coating based on the number of overprints.

[0031] FIG. 3 is a magnified morphological analysis of the upper surface of a platform according to an exemplary embodiment of the present invention and is presented as (i) bare silver electrode, (ii) one printed layer, (iii) three printed layers and (iv) six printed layers where the scale bar is 300 nm.

[0032] FIG. 4 is a graphical representation of the service roughness of the coating dependent upon the number of overprints.

[0033] FIG. 5 is a surface morphology analysis of a zinc oxide coating on a silver electrode magnified such that the scale bar is representative of 300 nm and indicated line profiles show the height of the coating on top of the silver particles in the dashed line and in the low regions of the silver electrode surface as shown in the blue solid line.

[0034] The steps of manufacturing a platform according to an exemplary embodiment are outlined below.

[0035] An organic substrate such as polyimide (PI) 10 is provided and cleaned ready for electrode printing. A suitable printing material is silver ink which can be printed, preferably via flexographic printing, onto the substrate. The ink is placed onto an anilox roller that transfers a controlled volume of ink to the printing plate which subsequently prints the desired electrode pattern 12 onto the substrate. The electrode pattern is preferably an interdigitated pattern of electrodes as shown in FIG. 1b which presents four bio-sensing platforms having zero, one, three and six overprints thereon as indicated by reference numerals 2, 4, 6 and 8 respectively. Optimised parameters for printing the silver ink are summarised below in table 1. After printing silver electrodes the samples are dried and the silver ink may be sintered by an annealing process.

[0036] The precursor, which in the exemplary embodiment will be referred to as zinc acetate, is then printed over the top of the electrodes again using the optimised parameters summarised in table 1. A plurality of layers of precursor solution may be printed over the electrodes with a drying step in between each printing step to dry the print layer before subsequent printing of another layer. Immediately after printing the drying step is completed at an elevated temperature such as 150° C. for approximately 30 seconds to dry the precursor before printing the next layer. A degree of transformation of the drying precursor will occur to form a metal oxide.

[0037] A transformation step is carried out after the final overprinting layer to ensure maximised conversion of zinc acetate to zinc oxide. This process of the transformation step may comprise placing the platform in an oven at approximately 300° C. for 30 minutes to allow full conversion of the zinc acetate to zinc oxide. This process leads to a nanotextured zinc oxide surface ideal for high loading of bioreceptors.

TABLE-US-00001 Ag Ink ZnA Ink Anilox roller volume   8 cm.sup.3m.sup.−2  12 cm.sup.3m.sup.−2 Anilox force 50N 125N Printing force 50N 150N Printing speed 0.8 ms.sup.−1 0.2 ms.sup.−1

[0038] The transformation step comprises a different protocol to the drying step, and preferably comprises a heat treatment process. This is to ensure full conversion of the zinc acetate to zinc oxide. It will also be appreciated that the transformation step may follow after a drying step, or directly after a precursor over printing step, however for manufacturing ease the transformation step will follow a drying step.

[0039] The transformation step is important as thermal decomposition of zinc acetate will form zinc oxide 14. A temperature of 300° C., which is 50° C. less than the glass transition temperature of the substrate (PI) is desirable. The transform protocol may comprise maintaining at a temperature of approximately 300° C. for 30 minutes. It will be appreciated that the annealing time in the transformation step may be reduced to well below 30 minutes, however it has been determined that 30 minutes maximises the effect of transformation from zinc acetate to zinc oxide.

[0040] Referring to FIG. 2 it is preferred that a plurality of overprinting steps are carried out to add additional precursor solution to increase the thickness of the print layer. Printing can achieve roughly linear deposition and each printed layer is less than 500 nm, preferably less than 100 nm and even more preferably less than 60 nm. This is readily achievable using flexographic printing. Each printed layer of precursor and after subsequent drying adds approximately 7-10 nm to the total thickness of the zinc oxide structure.

[0041] The printed zinc acetate layers followed by thermal decomposition results in a polycrystalline zinc oxide coating. Scanning electron microscope (SEM) images shown in FIG. 3 illustrate that the resultant zinc oxide layer, after the transformation step, is made of many interconnected zinc oxide particles with a size of a few nanometres. It is important that the resultant coating of zinc oxide is polycrystalline and after the transformation step it is difficult to distinguish between the individual layers. Referring to FIG. 3(i) the bare silver electrode is shown showing the submicron grains. The subsequent images show the density of the nanoparticles on the surface of the silver grains increasing with increasing number of overprint steps. For a single overprint onto the silver electrode as shown in FIG. 3(u) it can be seen that the density of the nanoparticles is non-uniform with a lower density in the higher regions of silver and a higher density in the troughs. Thus, non-uniform zinc oxide nanoparticles on the rough silver electrode surface is shown. As shown in FIG. 3(iii) the number of overprint layers has increased to three and as shown in FIG. 3(iv) the surface is shown after six overprint layers. As can be seen after six prints, aggregated zinc oxide nanoparticles can be seen across the entire silver electrode.

[0042] It is beneficial that the surface is rougher to provide increased surface area in order to increase the number of bio-receptors attaching at the surface.

[0043] FIG. 4 represents a graphical representation of the surface roughness against the number of overprint steps. FIG. 5 is an atomic force microscope image of surface morphology of the zinc oxide structure and indicated line profile shows the height of the structures on the top of the silver particle as a dashed line and in the lower regions of the silver surface in the solid line. This provides an extremely good surface for bio-receptor attachment. The height was found to vary between the high and low regions of the submicron grains of silver which can be attributed to the pooling of ink on the low regions and also the low regions experiencing reduced contact with the printing plate. The formation of these nanotextured features may occur during the drying step of the precursor between each subsequent print. The evaporation of liquid occurs more readily at points of surface imperfection. These points of evaporation will induce Marangoni flow creating a high point in the surface after drying due to the mass flow of the zinc acetate precursor to the area of evaporation. These surface imperfections may encourage evaporation at the same point in the subsequent printed layers. In this way, the phenomenon will increase the size of these nanotextured features with further print and dry cycles. The sensitivity of the biosensors may thus be enhanced. It is preferred as presented that approximately six overprinting stages are carried out.

[0044] As the nanotextured surface features are larger than the antibody, improved surface area allows more antibodies to attach to the surface. With the formation of this low cost mass producible metal oxide (zinc oxide) layer suitable for biosensing, a high volume low cost method of manufacturing a platform for use in biosensing applications is achieved.

[0045] The present invention has been described by way of example only and it will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims.