Method for preparing a surface with a controlled coverage of nanograde particles

Abstract

The present invention regards nano surfaces and particularly a gradient based nano surface. According to embodiments of the invention a surface bound gradient is created by distributed nanoparticles along a plane surface. This procedure greatly reduces the number of prepared surfaces needed, as well as the methodological error of analysis of adsorption and adhesion phenomena.

Claims

1. A solid surface with a continuous gradient of deposited, electrically charged nanoparticles, the nanoparticles having an average diameter between 10 and 60 nm, wherein the average center-to-center distance of the nanoparticles increases in a linear direction from 10 to 60 nm in one end of the gradient and about 100 to 150 nm in the other end of the gradient, and wherein the length of the continuous gradient is in a range of greater than 1 mm to 50 mm.

2. The surface according to claim 1, wherein the gradient is linear.

3. The surface according to claim 1, wherein the deposited, electrically charged nanoparticles and/or the surface consists of metal, ceramic, or polymer material.

4. The solid surface according to claim 1, wherein a compound is conjugated to the deposited, electrically charged nanoparticles and/or to the solid surface.

5. The surface according to claim 4, wherein the compound is selected from the group consisting of dithiol groups, thiol groups, PEG, and aminosilane.

6. A chip for use in analysis of adhesion phenomena, the chip comprising a surface according to claim 1, a first separate surface, and a second separate surface, wherein: the first separate and second separate surfaces are separated by barriers; and the first separate surface has a surface chemistry similar to the surface chemistry of the deposited, electrically charged nanoparticles and the second separate surface has a surface chemistry similar to the surface chemistry of the surface on which the electrically charged nanoparticles are deposited.

7. The chip according to claim 6, wherein the same type of compound is conjugated to the deposited, electrically charged nanoparticles and to the first separate surface, and wherein the compound is selected from the group consisting of thiol groups, PEG, and aminosilane.

8. The chip according to claim 7, wherein the same type of compound is conjugated to the surface on which the electrically charged nanoparticles are deposited and to the second separate surface, wherein the compound is selected from the group consisting of thiol groups; PEG; and aminosilane, and wherein the compound conjugated to the surface on which the electrically charged nanoparticles are deposited and to the second separate surface is different from the compound conjugated to the deposited, electrically charged nanoparticles and to the first separate surface.

9. The surface according to claim 1, wherein the deposited, electrically charged nanoparticles are gold nanoparticles.

10. The surface according to claim 5, wherein the compound is selected from the group consisting of methyl terminated thiols, amino terminated thiols, acid terminated thiols, peptide terminated thiols, saccharide-conjugated or PEG-conjugated thiols, thiol silanes, poly-L-lysine-PEG, PEG-modified silanes, malemide-PEG, and aminosilane.

11. The chip according to claim 8, wherein the deposited, electrically charged nanoparticles are gold nanoparticles.

12. The chip according to claim 6, wherein the same type of compound is conjugated to the deposited, electrically charged nanoparticles and to the first separate surface, and wherein the compound is selected from the group consisting of methyl terminated thiols, amino terminated thiols, acid terminated thiols, peptide terminated thiols, saccharide-conjugated or PEG-conjugated thiols, thiol silanes, poly-L-lysine-PEG, PEG-modified silanes, malemide-PEG, and aminosilane.

13. The chip according to claim 7, wherein the same type of compound is conjugated to the surface on which the electrically charged nanoparticles are deposited and to the second separate surface, wherein the compound is selected from the group consisting of methyl terminated thiols, amino terminated thiols, acid terminated thiols, peptide terminated thiols, saccharide-conjugated or PEG-conjugated thiols, thiol silanes, poly-L-lysine-PEG, PEG-modified silanes, malemide-PEG, and aminosilane, and wherein the compound conjugated to the surface on which the electrically charged nanoparticles are deposited and to the second separate surface is different from the one compound conjugated to the deposited, electrically charged nanoparticles and to the first separate surface.

14. The surface according to claim 1, wherein the deposited, electrically charged nanoparticles and/or the surface consists of glass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects, features and advantages of which the invention is capable, will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which

(2) FIGS. 1, 2A, 2B, and 2C are illustrations of prior art methods;

(3) FIG. 3 is an illustration of the physics of the DLVO theory;

(4) FIG. 4 is an illustration of the method according to an embodiment;

(5) FIG. 5 is an illustration of the method according to another embodiment;

(6) FIGS. 6A, 6B, and 6C are illustrations of an embodiment for making circular gradients;

(7) FIGS. 7A and 7B are illustrations of an embodiment with a circular gradient and scale marks applied to a surface;

(8) FIGS. 8A, 8B, and 8C are illustrations of a surface with a gradient and two separate reference surfaces;

(9) FIGS. 9A and 9B illustrate a set up for iSPR analysis;

(10) FIG. 10 illustrates an application of the present invention for studying cell interactions with surfaces;

(11) FIG. 11 is an overview of surfaces according to embodiments of the invention, analyzed with SEM;

(12) FIG. 12 shows results of two gradients, analyzed with SPR;

(13) FIG. 13 is a line scan of a gradient according to an embodiment, together with a line scan for a positive control surface; and

(14) FIGS. 14 to 16 are results of analyses according to embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

(15) Several embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in order for those skilled in the art to be able to carry out the invention. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The embodiments do not limit the invention, but the invention is only limited by the appended patent claims. Furthermore, the terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention.

(16) According to one aspect of the invention, a method for the convenient manufacture of surfaces with adsorbed nanoparticles with a gradient is provided. In an embodiment, the method may be described as follows.

(17) 1. One-dimensional Diffusion

(18) In an embodiment according to FIG. 4, a plane surface 203 with the ability to bind electrostatic surface charged nanoparticles 200 from an electrostatically stabilized particle solution is put in a vial 401. A salt free, or almost salt free, solution 402 with surface charged particles 200 is then added to the vial. A salt solution 403 with a relatively high density is carefully layered under the salt free solution 402 in a way so that the gravity dependent phase level between the solutions 403 and 402 is leveled with the lower part of the surface 203. In time, the salt solution 403 will diffuse into the salt free solution 402 and form a gradient of ionic strength in this.

(19) As will be appreciated by a person skilled in the art, the surface does not need to be plane, but may have any kind of curvature or shape.

(20) The electrostatic dependent repulsion between the particles is reduced when the ionic strength in the buffer close to the surface 203 increases. The particles therefore adsorb gradually closer to each other on the surface with the highest density of particles closest to the original phase level between the solutions 402 and 403. The lowest density of particles is found in the upper layer of the vial where the ionic strength is low and therefore the electrostatic repulsion is highest. After a controlled time of diffusion the solution is emptied from the vial, from below through the same tube 404 which was used when layering the salt solution 403 under particle containing salt free solution 402.

(21) In absence of convection and that the distance from the surface lower level, x=0 mm, to the bottom of the vial is sufficient, and that the distance from the surface lower level, x=0 mm, to the surface of the salt free solution 402 is sufficient, and that the diffusion is not allowed to continue for too long, the gradual distribution of the salt concentration in the solution above the surface 203 can be described with Fick's 2nd law of diffusion in one dimension:

(22) $\frac{?c}{?t}=D\frac{{?}^2}{?x^2}c$

(23) wherein, for the above mentioned conditions:

(24) $c\left(x,t\right)=\frac{1}{2}{c}_0\left(1-\mathrm{erf}\frac{x}{2\sqrt{\mathrm{Dt}}}\right)$

(25) where c is the molar salt concentration, x is the position in the vial in the relation x=0 (which coincides with the lower level of the surface 203), t is the time of diffusion, c.sub.0 is the salt concentration in the solution 403 at t=0, and D is the diffusion constant for the salt in question.

(26) This means that the length and the slope of the acquired particle gradient can be varied through changing the initial salt concentration c.sub.0 and the time of diffusion t which gives the method of manufacturing great flexibility.

(27) Further development of the invention described in FIG. 5 uses vials 501 which allow several surfaces to be used at the same procedure of diffusion as described in FIG. 4. An advantage of this method is that all surfaces in the vial will be exposed to the same solution of gold particles, molarity of the salt solution, and the time of diffusion. This assures that surfaces can be prepared with a high rate of conformity at the same preparation.

(28) The method of diffusion described in relation to FIG. 1 and earlier publications [11] has technical similarities with the described invention, but differs on several crucial aspects. The most important differences are: the component, nanoparticles, which will bind to the surface, is present as a constant concentration and does not diffuse as a gradient, the salt which diffuses does not bind to the surface; the gradient creating factor (gradient electrostatic repulsion between nanoparticles) takes place in the solution on the nanoparticles and not on the surface.

(29) 2. Two-dimensional Diffusion

(30) With the one-dimensional method of diffusion gradient surfaces are acquired in one dimension, e.g. high density of bound particles at one en of the gradient and a lower density in the opposite end. In an embodiment according to FIG. 6, making of circular gradients of particles on a surface is described. FIG. 6A is a side view and FIG. 6B is a top view.

(31) On the bottom in a Petri dish 601, a plane surface 203 is placed. A salt free, or almost salt free suspension 602 comprising nanoparticles and a matrix that allows diffusion of nanoparticles but at the same time prevent convection currents, is poured into the Petri dish. Such a suspension can consist of polysaccharides in a water containing particle form, e.g. gel particles used for gel filtration e.g. Sephadex g-25 or similar material. After a free solvent, e.g. water, is removed from the plane suspension layer, a reservoir 603, such as a round piece of blotter, is placed on the suspension. The reservoir 603 is previously filled with the salt solution 403 with high molarity, for example by soaking a blotter in such a solution. This system is then given time for diffusion. The solution 403 will diffuse in the suspension 602 and the circular diffusion front will after a while reaches the surface 203 which eventually will result in a circular surface with a radial concentration gradient of ions. Finally, the suspension 602 is flushed away with a solvent, e.g. water. The end result is a circular surface of adsorbed particles which density is highest in the middle of the surface and lowest towards the periphery.

(32) An important aspect of the described invention is the analytical dynamics, which is the range between that part of the surface gradient with the highest number of adsorbed particles per surface unit and the part of the same gradient surface with the lowest number of adsorbed particles per surface unit. The greater this range is, the more analytical information is obtained in adhesion and adsorption experiments. A methodological source of error can be electrically particles in low concentration in a salt free solvent such as water has a tendency to bind irregularly to surfaces in unpredictable patterns. Such irregular patterns make the interpretation of additional adhesion and adsorption experiments more difficult. In an embodiment according to FIG. 6C a method to prevent the formation of irregular patterns is provided. The method comprises mixing electrically charged, surface binding particles 200 with the electrically charged particles 604 which do not bind to the surface 203. The function of the latter particles is to improve the dispersion of the charged and the binding particles in the solution in order for pattern of binding not to become irregular.

(33) Typical Experiments and Evaluation Methods

(34) A gradient area with bound particles is normally between 1-50 mm, such as 1-10 mm. On this surface adsorption experiments with biopolymers and adhesion experiments with cells can be performed. The result of the experiments can then be correlated to a continuous gradient of bound nanoparticles per surface unit. In simple biopolymer adsorption experiments it is possible to use surface sensitive, optical methods. In experiments involving whole cells light microscopy can be used for detailed studies of the cells as well as fluorescent microscopy for studies of fine details.

(35) In one application of the invention, FIG. 7, the particle gradient is applied to a surface 700 to which a scale has been added to facilitate the analysis through a microscope. The scale marks can be vertical 702, horizontal 703 or radial 704. The scales and the scale marks can be in different ranges to accommodate different types of analysis e.g. mm range for ocular analysis or 10-500 micrometers range for the analysis for light microscopy or SEM which is described in FIG. 7B, 705. The scale marks can consist of engravings, completely or partly through the particle-binding surface, e.g. a dithiol modified gold surface, so that the underlying substrate, e.g. glass or silica, is exposed. Alternatively, the scale marks can be ridges, e.g. in gold, on a particle-binding surface, e.g. a thiol silane modified glass or silica surface. The surface pattern is preferably made with photo lithographical techniques.

(36) In another application of the invention, FIG. 8, a nanoparticle gradient surface 203 or 700 is present on a chip surface 800, e.g. a glass slide, together with two additional, separate surfaces 801 and 802. FIG. 8A is a top view and FIGS. 8B and 8C are side views according to two embodiments. The two additional, separate surfaces are chemically modified in such a way that one of the surfaces 802 is given the same surface chemistry as the surface with the nanoparticles, whereas the other surface 801 is given the same chemistry as the surface that surrounds the particles in the gradient. When all three surfaces are present in a biological experiment, e.g. bacterial adsorption, the operator can examine through a microscope whether the bacteria adsorbs to an area of the gradient surface. The operator also obtains information regarding how the bacteria adsorb to surfaces that do not contain nanoparticles but only unmixed surface chemistries. In this way the operator can determine whether the adhesion of the bacteria is related to the presence of nanoparticles or not, and which particle density is necessary for adsorption. The different surfaces 203/700, 801, an 802 can be separated on the chip 800 with the help of barriers 803 in order to facilitate the use and fabrication of the surface. The barriers can be made of engravings or spaces between the surfaces 203/700, 801, and 802 on the chip 800 in such a way that the underlying substrate 804 is exposed. Alternatively, the barriers can consist of ridges between the surfaces 203/700, 801, and 802, specifically in those cases where the particle gradient has been applied on the underlying substrate 804.

(37) An application of the invention is a product, e.g. a chip comprising a surface, e.g. a glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a dithiol modified gold surface on which free dithiols between the particles has reacted with malemide-PEG and the surface of the particles has reacted with a functional thiol, e.g. methyl terminated, amino terminated, acid terminated, or peptide terminated; 2, a gold surface which has been modified dithiol and malemide-PEG; 3, a gold surface which has been modified with the same functional thiol as the surface on the particles.

(38) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a dithiol modified gold surface on which free dithiols between the particles has reacted with a malemide-conjugated molecule, e.g. methyl terminated, amino terminated, acid terminated, or peptide terminated, phosphorylated, heterocyclics, aromatics, carbonyles, sugars, inorganics, metal containing particles and the surface of the particles has reacted with a PEG-conjugated thiol. 2, a gold surface which has been modified with dithiol and malemide-conjugated molecules, e.g. methyl terminated, amino terminated, acid terminated, or peptide terminated; 3, a gold surface which has been modified with the same functional thiol as the surface on the particles.

(39) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a dithiol modified gold surface on which free dithiols between the particles has reacted with malemide-PEG; 2, a gold surface which has been modified dithiol and malemide-PEG; 3, a pure gold surface. With this product, the operator can choose which thiol reagent that should be used. There is a large number of commercially available thiols that can affect adhesion, e.g. thiols conjugated with amino groups, mono- and polysaccharides.

(40) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a dithiol modified gold surface; 2, a gold surface which has been modified dithiol; 3 a pure gold surface. With this product the operator can choose both which malemide reagent to be bound between the panicles and which thiol reagent to be bound on the particles. The possibilities to alter an experiment will therefore increase further.

(41) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol silane modified glass- or silica surface, where free thiol silanes between the particles has reacted with malemide PEG, and where the surface on the particles has reacted with the functional thiol, e.g. methyl terminated, amino terminated, acid terminated, or peptide terminated; 2, a glass or silica surface which has been modified with thiol silane and malemide-PEG; 3, a gold surface which has been modified the same functional thiol as the surface of the particles.

(42) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol silane modified glass- or silica surface, where free thiol silanes, between the particles, have reacted with malemide PEG; 2, glass- or silica surface which has been modified with thiol silane and malemide PEG; 3, an unmodified gold surface. With this product the operator can choose which thiol reagent to be used.

(43) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol- or aminosilane modified glass- or silica surface, where the silanes under and between the particles has been removed in such a way, e.g. trough plasma treatment, that the particles are sintered on the glass or silica surface where the surfaces between the particles has reacted with PEG-Silane and the surface of the particles has reacted with a functional thiol, e.g. methyl terminated, amino terminated, acid terminated or peptide terminated; 2, a glass or silica surface which has been modified PEG-Silane; 3, a gold surface which has been modified with the same functional thiol as the surface of the particles.

(44) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol- or aminosilane modified glass- or silica surface and the surface of the particles has reacted with a functional thiol, e.g. PEG terminated, methyl terminated, amino terminated, acid terminated or peptide terminated; 2, a glass or silica surface which has been modified with thiol- or aminosilane; 3, a gold surface which has been modified with the same functional thiol as the surface of the particles.

(45) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol- or aminosilane modified glass- or silica surface, where the silanes under and between the particles has been removed in such a way, e.g. trough plasma treatment, that the particles are sintered on the glass or silica surface where the surfaces between the particles have reacted with PEG-Silane; 2, a glass or silica surface which has been modified PEG-Silane; 3, an unmodified gold surface. With this product an operator can choose which thiol reagent to be used.

(46) An application of the invention is a product comprising a surface, e.g. glass slide with the three surfaces mentioned above; 1, gold nanoparticle gradient surface where the gold nanoparticle gradient is manufactured on a thiol- or aminosilane modified glass- or silica surface, where the silanes under and between the particles has been removed in such a way, e.g. trough plasma treatment, that the particles are sintered on the glass or silica surface; 2, a glass or silica surface; 3, an unmodified gold surface. With this product the operator can choose which surface chemistry and method of modification for the different surfaces.

(47) For the above-mentioned applications the three typical surfaces can in manufacturing be made separate, and then be combined on the glass slides with an adhesive. It is also possible to prepare these surfaces directly on a glass slide.

(48) For simple biopolymer adsorption experiments, surface sensitive optical methods such as ellipsometry and surface plasmon resonance (SPR) can be used. A special case of SPR is that so called imaging SPR (iSPR) method which allows for simultaneous quantification of both adsorbing nanoparticles and the following bio adhesion in a complete gradient area (see example). A set up for iSPR analysis of a gradient surface is illustrated in FIG. 9A. An apparatus 900 for imaging SPR such as described in [17], normally controlled with a computer 905, is applied in contact with an SPR-substrate usually comprising a glass surface 901 on which a thin gold layer 902 has been applied. Above the gold layer a chamber 904 containing a solution is placed, e.g. a buffer in such a way that the gold layer is in contact with the solution. The chamber 904 can have an inlet 907 and an outlet 908 and function as a perfusion system to transport solution and analytes to and from the surface.

(49) In an application of the invention the gold surface 902 has been chemically modified with the layer 903 to bind nanoparticles from solution, and a gradient of nanoparticles has been applied to the surface. At analysis the SPR-response from different positions on the gradient surface can be correlated to partial density at this position. In the case bio adhesion, e.g. protein-, thrombocyte-, or bacterial adsorption takes place to the gradient surface this can also be detected as an additive response, FIG. 9B.

(50) Lately, electrochemical technologies, particularly measurements of impedance have been used to study cell interactions with surfaces [18]. Electrochemical technologies can also be used to estimate the number of nanoparticles on an electrode surface. This specifically is true for conducting nanoparticles for instance gold [19]. In an application of the invention described in FIG. 10 a nanoparticle gradient is applied on a surface 1000 which is made up of n particle binding surfaces 1001 of an electrically conducting material which has been modified with the chemistry 1003 to bind nanoparticles. The surfaces 1001 is place on a non conducting substrate 1002 in such a way that the surfaces 1001 an act as electrodes electrically isolated from one and other. The nanoparticle gradient is manufactured in such a way that the particle binding electrode surface 1 on the surface 1000 gets a high particle density while the particle binding electrode surface n on the surface 1000 gets low particle density. This is possible by using the surface 1000 such as surface 203 in FIG. 4 and let position 0 on the surface 1000 coincide x=0 in FIG. 4.

(51) The surface 1000 is applied in contact with an electrolyte, e.g. a buffer, in an electrochemical cell 1004 which also can have an inlet 1005 and an outlet 1006 in order to facilitate transportation of electrolyte and analyte to the surface 1000. In addition to the electrodes 1-n localized on the surface 1000, it is necessary for some applications to add an additional reference electrode 1007 and a counter electrode 1008 applied in the electrolyte. In some applications the electrodes 1007 and or 1008 can also be placed on the surface 1000. All electrodes 1-n on the surface 1000 and in some cases 1007 and 1008, are connected individually by a system for electrochemical reference 1009. The system 1009 can be a system capable of different types of electrochemical reference, e.g. voltammetry, amperometry, coulometry, impedance spectroscopy or impedance determination. Alternatively the system 1009 could be a system designed for a single type of electrochemical measurements such as impedance measurements. The electrochemical response from the different electrodes on the surface 1000 can be measured either between different electrodes on the surface 1000, or by using the electrodes 1007 and 1008 in a conventional tri electrode setup [20]. When measuring, the electrochemical response from different electrodes with different positions on the surface 1000 can be correlated to the particle density at this position. If bio adhesion, e.g. cell adhesion, takes place to the gradient surface this can also be detected as an additive, usually a negative, change of the electrochemical response. If a redox active substance comes in contact with the surface this can also be detected as an additive, usually a positive change of the electrochemical response.

EXAMPLE 1

Evaluation of Gradual Particle Adsorption with SEM

(52) Gold surfaces with size 11?20 mm were manufactured by evaporation of first 5 nm Cr and then 200 nm Au on a substrate of SiO2. These were washed and provided with a monolayer of dithiol according to the procedure described in detail [1, 8]. In short, the clean gold surfaces were incubated in a solution of octane dithiol in ethanol where they were reactivated with dithiolthreitol (DDT). An electrostatically stabilized gold particle solution with gold particles around 10 nm in diameter was manufactured according to the procedure described in detail [1, 8]. The gold solution was centrifuged at 16000 g to reduce the ionic strength in the solution, and in order to increase the concentration of the particles. After centrifugation the gold particle pellet was diluted to an approximate particle concentration of 55 nM in pure water with the conductivity of 18.2 M?*cm. This particle solution was transferred to a container designed gradient manufacturing according to FIG. 5 after which a number of the dithiol prepared surfaces were placed in the same container with a specific distance to the bottom the same. There after a citrate buffer with the concentration 1M and pH 4.0 was placed at the bottom of the gradient container so that the space underneath the surfaces was filled with this buffer. The citrate buffer was then allowed to diffuse over the surfaces during 30 minutes after which the procedure was stopped by emptying the solution from the gradient container from below. In a different application the citrate buffer with the concentration 50 mM was applied underneath the surfaces and was the allowed to diffuse less than 90 minutes which results in a longer gradient with less slope compared to the one obtained with 1 M buffer under 30 minutes. The surfaces were analyzed with SEM at different positions on the gradient surface. A selection of pictures is presented in FIG. 11.

EXAMPLE 2

Evaluation of Gradual Particle Adsorption by iSPR

(53) Linear gradients with 10 nm gold nanoparticles were prepared as described in example 1 by dithiol chemistry. As a substrate glass surfaces on which a thin layer of Au, app. 50 nm, had been evaporated was used. These surfaces are suitable for analysis by surface Plasmon resonance, SPR, after the manufacture of gradients the surfaces were placed in an instrument for imaging SPR which is described in detail in [17]. Two different gradients were analyzed, see FIG. 12. One gradient had been prepared with 50 mM citrate buffer which has been allowed to diffuse for 90 minutes (long gradient), and one gradient had been prepared with 1 M citrate buffer for 30 minutes (short gradient). Each particle gradient also had reacted with maleimide-PEG in order minimize bioadhesion between the distributed particles, and with octane thiol above the particles which makes the surfaces on the particles hydrophobic in order to promote bio adhesion. On each gradient surface an area of app. 1?5 mm was analyzed. In these areas all essential parts of the gradient was pictured. The SPR wave length presented in the 3D graph z-axis is proportional to the surface coverage of gold nanoparticles. In FIG. 13 a line scan of a short gradient is presented together with a line scan for a positive control surface, (in this case a surface modified with only octanedithiol), and a negative control surface modified with octane dithiol and maleimide-PEG. Each line scan represents an average of all scans of the surface.

EXAMPLE 3

Evaluation of Fibrinogen Adsorption and Thrombocyte Adsorption to Hydrophobic Nanoparticle Gradients with iSPR and Fluorescence Microscopy

(54) Short gradients with 10 nm gold nanoparticles were manufactured on gold surfaces designed for SPR analysis, and were then modified by malemide-PEG and octanethiol according to example 2 above. This gives gradients of hydrophobic particles against the background of protein rejecting PEG. The surfaces were analyzed with iSPR. In a sequence fibrinogen (0.5 mg/ml in PBS) for 5 minutes and then thrombocytes (essentially a serum free preparation from a healthy donor) for 30 minutes were adsorbed to surfaces with gradients, positive control surfaces (only dithiol), and negative control surfaces (dithiol modified with malemide-PEG). In FIG. 14 the response from fibrinogen and thrombocyte adsorption is presented for a gradient surface and a positive controlled surface. The blue curve shows the adsorption of fibrinogen, the green curve the accumulated response from both fibrinogen and thrombocytes. The response from the underlying surfaces, corresponding to what is shown in FIG. 13, has been subtracted from the results in FIG. 14. Note that the positive surface adsorbs both fibrinogen and thrombocytes homogeneously across the surface, while the gradient surface adsorbs both protein and thrombocytes gradually. The negative control surfaces gave no significant response. After thrombocyte adsorption the surfaces were washed with PBS buffer and fixated for 15 minutes with 2% glutaraldehyde. The surfaces were stained (staining of the actin skeleton) according to a normal protocol and were analyzed fluorescence microscopy at different positions at the surfaces. FIG. 15 shows representative thrombocytes at positions with high (A) and low (B) particle coverage respectively.

EXAMPLE 4

Evaluation of Microbial Adhesion to Hydrophobic Nanoparticle Gradients

(55) Long gradients with 10 nm gold nanoparticles were manufactured on gold surfaces modified with malemide-PEG and octane thiol according to example 2 above. This gives gradients with hydrophobic particles against the background of protein rejecting PEG. Fimbriated E. coli were adsorbed to the surfaces under static conditions, and were exposed to a controlled wash for 10 minutes. Remaining bacteria were stained with acridine orange and DAPI after which the surfaces were analyzed under magnifying glass and fluorescence microscopy. FIG. 16 shows a section of a gradients surface with adsorbed E. coli stained with acridine orange at low magnification together with a positive control surface (octane thiol) and negative control surface (dithiol modified with malemide-PEG). The surface coverage of nanoparticles at different positions in the gradient was determined by SEM. The relative surface coverage is shown in each picture. The inserted picture shows two bacteria stained with DAP at greater magnification. The distribution of bacteria changes dramatically at 20% surface coverage.

(56) Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims.

(57) In the claims, the term comprises/comprising does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms a, an, first, second etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

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