WO2003104775A1

WO2003104775A1 - Method for protein chip analysis by using surface plasmon resonance spectroscopic imaging technology

Info

Publication number: WO2003104775A1
Application number: PCT/KR2002/001659
Authority: WO
Inventors: Kwon Soo Ha; Jong Seol Yuk; Sun Ju Yi; Hyeon Gon Lee; Kyung Hoon Kwon
Original assignee: Korea Basic Science Institute
Priority date: 2002-06-08
Filing date: 2002-09-02
Publication date: 2003-12-18
Also published as: AU2002337504A1

Abstract

The present invention provides a method for protein chip analysis by using surface plasmon resonance spectroscopic image technology. A protein chip with a plurality of spots, arranged at a specific interval in vertical and horizontal directions, is mounted on a x-y stage, and p-polarized beams that passed through a prism are sequentially irradiated on each spot of the protein chip. The light signal reflected from each spot of the protein chip is collected into a spectrometer and its surface plasmon resonance wavelength is determined. This surface plasmon resonance wavelength value is represented by a color at the position of each protein spot to obtain a two dimensional image. Otherwise, the surface plasmon resonance wavelength value is allocated to a z-coordinate value to obtain a three-dimensional image.

Description

METHOD FOR PROTEIN CHIP ANALYSIS BY USING SURFACE PLASMON RESONANCE SPECTROSCOPIC IMAGING TECHNOLOGY

Technical Field The present invention relates to a method for spectroscopic imaging of protein chip by using white-light surface plasmon resonance and a method for analyzing a protein chip using the same.

Background Art In general, an image using an optical device can be obtained by a CCD camera.

In this case, images can be captured by the light reflected from the surface of an object to be analyzed. However, it is difficult to obtain the image of an object if there is no enough light reflected from the surface of the object. It is also difficult to obtain clear images of objects by regular optical devices when the position of the object device is not vertically aligned with the surface of object to be observed. In addition, it is difficult to analyze the fine structure of object by regular optical devices in real time.

The phenomenon of surface plasmon resonance has been widely used for analyzing various biomolecule interactions including antigen-antibody interactions on protein chip. However, it is not possible to analyze the whole surface area of protein chip by the previous methods, since a local point or only a small area of protein chip surface can be analyzed by the methods.

It is essential to analyze the surface plasmon resonance signal at the center of each spot of protein chip when protein chip with hundreds to thousands protein spots are analyzed. A CCD camera can be used to determine the center of each spot of protein chip, but it is not possible to obtain desired results because the reflected light from the protein chip is interfered with the light emitted from the CCD camera. Furthermore, the object to be analyzed is tilted because the optical devices are made according to the Kretschmann-Raether geometry. Consequently, it is impossible to use the devices such as CCD camera, currently available, to find the center of protein chip.

Disclosure of Invention

The purpose of the present invention is to provide a noble method for imaging of biomolecule interactions on the surfaces of protein chip by the phenomenon of surface plasmon resonance.

Another purpose of the present invention is to provide a rapid and accurate method to analyze protein chip by the imaging method. To accomplish the purposes, the bottom surface of slide glass was fabricated with metal film, such as gold, and the gold surface was deposited with protein or polymer layers. And, distilled water or emulsion oil as an index matching solution was applied to the top surface of a protein chip and a prism was located on the slide glass containing the index matching solution to construct an optical coupler. Then, P- polarized beam, obtained by converting white-light by a polarizer, was passed through the prism and exposed to the protein chip, and then the difference between the surface plasmon resonance wavelength of the reflected light from protein or polymer-bound surface and that from protein or polymer-free surface was used to construct two- and three-dimensional images of protein chip. According to the present invention, biological interactions on the protein chip can be accurately analyzed by two- or three-dimensional imaging.

Furthermore, the present invention with respect to the method of analyzing a protein chip uses a white-light source with various wavelengths and a X-Y linear stage, on which the protein chip is mounted, and the reflected light from the surface of the protein chip is collected into a small-size optical fiber to obtain a surface plasmon resonance signal. And, the surface plasmon resonance signal obtained from the metal surface of the protein chip is discriminated from the noise obtained from a substrate slide glass. Next, multiple surface plasmon resonance wavelengths obtained from a reference spot of a protein chip are analyzed to determine a central coordinate of the reference spot, and then protein chip is analyzed by measuring surface plasmon resonance wavelength at the center of every spot. The protein chip is also analyzed by measuring surface plasmon resonance wavelengths from the whole surface area thereof, which is divided into a plurality of pixels.

According to the protein chip analysis method by the present invention, it is possible to determine the reference position of protein chip without an additional expensive camera or CCD camera with low intensity. In addition, the present invention can improve the accuracy and efficiency of protein chip analysis. Brief Description of the Drawings

Further objectives and advantages of the invention will be fully understood from the following detailed description with the accompanying drawings;

FIG. 1 schematically illustrates the system configuration used for performing a protein chip imaging method according to the present invention;

FIG. 2 schematically illustrates the components of a protein chip according to the present invention;

FIG. 3 illustrates the conceptual diagram for obtaining an image of a protein chip according to the present invention; FIG. 4 illustrates a two-dimensional image of one spot of a protein chip according to the present invention;

FIG. 5 illustrates a three-dimensional image of one spot of a protein chip according to the present invention;

FIG. 6 illustrates a plurality of pixels of a protein chip for imaging according to the present invention;

FIG. 7 illustrates a conceptual diagram to find the central coordinate of the reference spot of a protein chip according to the present invention;

FIG. 8 illustrates image of the protein chip analyzed by spot scanning method according to the present invention; FIG. 9 illustrates a two-dimensional image of protein chip analyzed by whole scanning method according to the present invention; and

FIG. 10 illustrates a three-dimensional image of the protein chip analyzed by a whole scanning method according to the present invention.

Best Mode for Carrying Out the Invention

The present invention will be now described in detail according to the accompanying drawings.

FIG. 1 schematically illustrates a system to construct the protein chip image according to the present invention. In FIG. 1, reference numeral 1 denotes a light source emitting white-light. The white-light, emitted from the light source 1, passes through at least a pair of convex lenses 2 and 4, and is focused. An iris 3 that controls the quantity of light is aligned between the pair of convex lenses 2 and 4. The light that has passed through the pair of convex lenses 2 and 4 is converted into P-polarized by a polarizer 5. The p-polarized light is reflected from mirrors 6 and 7 above the critical angle at which total reflection occurs.

The polarized beams, reflected from the mirrors 6 and 7, pass through a prism 9 and arrive onto the protein chip 10 that is mounted on a linear stage 16 designed to move in X-Y directions.

As shown in FIG. 2, the protein chip 10 includes a BK-7 slide glass 11, a thin metal film 13 such as gold film formed on the bottom side of the slide glass 11, protein films 14 and 15 or polymer layers on the metal film. Each of the protein layers 14 and 15 is divided into a plurality of pixels 14a- 14n and 15a- 15n.

Distilled water or emulsion oil 12 is applied onto the top surface of the slide glass 11 of the protein chip 10 and prism 9 is placed on it to make an optical coupler. The prism 9 and the thin metal film 13 should not directly contact each other. The thin metal film 13 is in contact with air or fluid. The distilled water or emulsion oil layer 12 is used for reducing a refractive index difference between the prism 9 and the slide glass 11.

The polarized beams pass through the prism 9 and arrive onto the gold film 13 of the protein chip 10. At this time, the stage 16 is sequentially moved in X-Y directions so that the reflected lights from the pixels 14a-14n and 15a-15n of the protein chip 10 are collected into an optical fiber 20. The reflected lights from gold film 13 on the slide glass 11 generate surface plasmon resonance signals, but the gold-free area of the slide glass 11 does not generate the surface plasmon resonance signals.

The reflected lights from the pixels 14a-14n and 15a-15n of the protein chip 10 are collected into the optical fiber 20, aligned with the angle identical to the incident angle, and transferred into a spectrometer 30. The optical coupler can be moved or the optical fiber 20 can be directly and sequentially moved so that signals generated from the pixels are sequentially detected by the optical fiber 20.

The surface plasmon resonance wavelength can be determined by data analysis based on the signals obtained from the spectrometer 30. At this time, the optical fiber 20 may include a plurality of strands to receive a plurality of signals generated from the pixels of the protein chip 10.

The method for imaging the protein chip 10 according to the present invention is explained in detail below; To obtain the image of the protein chip using the surface plasmon resonance, first of all, the size of each pixel of the chip is determined according to the following expression 1, where n is the number of pixel to determine the pixel size. When n is bigger, the size of pixels becomes smaller and the resolution of images is better. The surface of a protein chip is divided into a plurality of pixels by the expression 2 and the position of each pixel is determined. The process is shown in FIG. 3(a).

[Expression 1]

Pixel size = (protein chip size)/n

[Expression 2] Rl l R12 ... Pin

R21 R22 Pin

Pn\ Pnl Pnn

After the protein chip is divided into a plurality of pixels by the expression 2, x and y position of each pixel is represented by the matrix of the expression 3. For example, the position of pixel Pnn corresponds to Ann. Accordingly, the matrix size of the expression 3 is identical to that of the expression 2.

[Expression 3]

Lights are reflected from the position of the pixels 14a-14n and 15a-15n of the protein chip, represented in the expression 3, and collected into the spectrometer 30. Then, the surface plasmon resonance wavelength corresponding to the smallest value among the signals is calculated by the fourth polynomial curve fitting.

At this time, the surface plasmon resonance wavelength at each pixel of the metal film 13 without polymer or protein films 14 and 15 is obtained and used as the minimum reference of the barometer as shown at the right upper of FIG. 4. the polymer or protein layers 14 and 15 to be analyzed are formed on the thin metal film 13 of the protein chip 10, and the surface plasmon resonance wavelength at each pixel is obtained according to the above method. The obtained surface plasmon resonance wavelength becomes the maximum reference of the barometer for imaging as shown at the right upper part of FIG. 4. That is, the surface plasmon resonance wavelengths, which are obtained from the thin metal film 13 and protein films 14 and 15 or polymer, are used as the minimum and maximum reference values for imaging. The maximum and minimum wavelengths are represented by red and blue colors, respectively, and the medium value is represented by green color. And the intermediate wavelengths are shown by adjusting brightness and chroma of the colors.

As shown by the expression 4, the surface plasmon resonance wavelength obtained from each pixel is summed up to make a two-dimensional image. Surface resonance plasmon wavelength at each pixel is assigned into the appropriate color in proportion to the wavelength at the coordinate of each pixel. Finally, a two- dimensional image of one spot of the protein chip is made as shown in FIG. 4. [Expression 4]

The surface resonance plasmon wavelength of each pixel is allocated to a z coordinate value with respect to x and y coordinates of the pixel and a three-dimensional image was constructed as shown in FIG. 5.

In addition to analysis of the protein chip, the present invention can be applied as a noble technology to analyze the thickness or surface roughness of metal or polymer films by surface imaging.

Thus, interactions of biomolecules such as proteins and DNA on the protein chip can be quickly and easily analyzed by the present imaging method.

Moreover, the protein chip can be analyzed according to the present invention as follows; The light emitted from the light source is converted into p-polarized beams using the system shown in FIG. 1, and the p-polarized beams pass through the prism 9 and arrive onto the surface of the protein chip 10. The p-polarized beams are reflected from the surface of the protein chip and collected into the spectrometer 30 through a plurality of the optical fibers aligned with the identical angle to the incident angle. The surface plasmon resonance wavelength is calculated from the signals collected into the spectrometer by the fourth polynomial curve fitting.

To obtain an image of the protein chip by surface plasmon resonance phenomena, first, the pixel size is determined according to the expression 1, where n is the number to determine the pixel size. When n is bigger, the pixel size becomes smaller and the resolution is better. The protein chip is divided into a plurality of pixels by the expression 2 and the position of each pixel is determined. The process is shown in FIG. 5 6.

After the protein chip is divided into a plurality of pixels, x and y positions of each pixel is represented by the expression 3. That is, the position of pixel Pnn corresponds to Ann. Thus, the size of the matrix of the expression 3 is identical to the matrix of the expression 2.

10 In order to measure a surface plasmon resonance wavelength from each spot of protein chip, it is necessary to find the coordinate values of a reference spot. The coordinate values of an arbitrary reference spot are determined by the following method. As shown in FIG. 7, the reference spot of protein chip is divided into a plurality of pixels and surface plasmon resonance wavelengths are measured to construct a two-

15 dimensional image. Then, minimum and maximum values of surface plasmon resonance wavelengths, x- and y-axes, Xmin and Xmax and Ymin and Ymax, respectively, are obtained, and then used to determine the central coordinate of the reference spot according to the expression 5. [Expression 5] _ ( min+ Zmax,7min+ 7 max)

Then, as shown in the expression 6, a plurality of spots of the protein chip are exposed to the p-polarized beam while the protein chip is sequentially moved in x and y directions from the coordinate of the reference spot. The surface plasmon resonance wavelength, which is corresponding to the smallest intensity, is determined from the

25 reflected signal from each pixel by using the fourth polynomial curve fitting. Then, the difference between the surface plasmon resonance wavelength on every pixel with and without protein or polymer is calculated. The appropriate color with the brightness and chroma corresponding to the difference is presented at each pixel to make the two- dimensional images as shown in FIGS. 8 and 9.

30 In FIG. 8, blue and red represent minimum and maximun differences of surface plasmon resonance wavelengths, respectively. [Expression 6] Measurement point=(Xc+δx, Yc+δy)

As another method, when the surface resonance plasmon wavelength of each pixel of protein spot is allocated to a coordinate of z-axis with respect to x and y coordinate of the corresponding pixel, protein chip is analyzed by a three-dimensional image as shown in FIG. 10.

Industrial Applicability

As described above, the present invention can provide a new method to analyze protein chip by two- or three-dimensional images, which are constructed by using the surface plasmon resonance wavelength obtained by irradiating p-polarized beam on the protein or polymer layer of protein chip. Accordingly, the invention can be used for analyzing biomolecule interactions on protein chip ex situ and in situ. Furthermore, when polymer is deposited instead of protein, a variation of polymer surface can be easily analyzed. While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

What is claimed is:

1. A method for analyzing a protein chip having a plurality of protein spots on the bottom surface of a slide glass with a layer of thin metal film interposed therebetween, comprising the steps of: mounting the protein chip on a movable x-y stage; depositing an optical coupler, including a prism with distilled water or emulsion oil applied on the base thereof, on the top surface of the slide glass of the protein chip; dividing the surface of each protein spot into a plurality of imaginary pixels and allocating x-y coordinates to each of the pixels; sequentially irradiating the p-polarized beams through the optical coupler onto each pixel of the protein spot by moving the stage in x and y directions; collecting the surface plasmon resonance wavelengths from the pixels of the whole protein spots through at least one optical fiber in a spectrometer; calculating the differences between the surface plasmon resonance wavelength from the pixels on the protein-bound metal film and that from protein-free metal film; and allocating a color with the brightness and chroma corresponding to the differences of the surface plasmon resonance wavelengths to each pixel to display two- dimensional images of the protein spots in the protein chip.

2. The method as claimed in claim 1, wherein the layer of metal film comprises a lower metal film selected from a group consisting of titanium, chrome, nickel and aluminum, and an upper metal film selected from a group consisting of gold, silver, copper and aluminum and being deposited on the lower metal film.

3. The method as claimed in claim 1, wherein the surface of the protein chip is in contact with air or fluid.

4. The method as claimed in claim 1, further comprising the step of allocating the surface resonance plasmon wavelength of each pixel to a z coordinate value thereof to display three-dimensional images of the protein spots in the protein chip.

5. A method for analyzing a protein chip having a plurality of protein spots on the bottom surface of a slide glass with a layer of thin metal film interposed therebetween, comprising the steps of: mounting the protein chip on a movable x-y stage; depositing an optical coupler, including a prism with distilled water or emulsion oil as an index matching solution applied on the base thereof, on the top surface of the slide glass of the protein chip; dividing the surface of a reference protein spot of the protein chip into a plurality of imaginary pixels and allocating x-y coordinates to each of the pixels; irradiating p-polarized beams onto the whole pixels of the reference protein spot through the optical coupler; collecting surface plasmon resonance wavelengths from the pixels of the reference protein spot in a spectrometer through at least one optical fiber; setting averages of a minimum and a maximum x-y coordinate values for the reference spot to the center thereof; irradiating the p-polarized beam sequentially onto the whole protein spots while sequentially moving the stage from the center of the reference spot by the distance between the protein spots along x-y directions; calculating the differences between the surface resonance plasmon wavelength from the pixel of protein spot on the metal film and that from protein-free metal film; and allocating a color with the brightness and chroma corresponding to the differences of the surface plasmon resonance wavelengths to each pixel to display two- dimensional images of the protein spots of the protein chip.

6. A method for analyzing a protein chip having a plurality of protein spots on the bottom surface of a slide glass with a layer of thin metal film interposed therebetween, comprising the steps of: mounting the protein chip on a stage movable along x and y directions; depositing an optical coupler, including a prism with distilled water or emulsion oil as an index matching solution applied on the base thereof, on the top surface of the slide glass of the protein chip; dividing the surface of a reference protein spot of the protein chip into a plurality of imaginary pixels and •allocating x-y coordinates to each of the pixels; irradiating p-polarized beams onto the whole pixels of the reference protein spot through the optical coupler; collecting surface plasmon resonance wavelengths from the pixels of the reference protein spot in a spectrometer through at least one optical fiber; setting averages of a minimum and a maximum x-y coordinate values for the reference spot to the center thereof; irradiating the p-polarized beam sequentially onto the whole protein spots while sequentially moving the stage from the center of the reference spot by the distance between the protein spots along x-y directions; calculating the differences between the surface resonance plasmon wavelength from the pixel of protein spot on the metal film and that from protein-free metal film; and allocating the surface resonance plasmon wavelength of each pixel to a z coordinate value thereof to display three-dimensional images of the protein spots of the protein chip.