The Research Of Reflectometry Difference Biosensor Based On Wavelength Modulation

The label-free optical biosensor based on Reflectometry Interference Theory hasthe advantages of simple optical system structure, strong electromagnetic immunity andhigh sensitivity. As a result, RIB has causing more and more attention in environmentalprotection, food monitoring and clinical medicine, etc. But it is difficult to detect largevolume samples simultaneously, making its application field limited. In order to meetthe need of high flux detection, this paper designs a new reflectometry differencebiosensor based on the wavelength modulation and provides the preliminaryexperimental study.First, in the theoretical analysis, we introduce thin film interference principle, thebasic theory of reflectometry difference biosensor. Single medium film model andabsorption base model are established to deduce the reflectance formula, respectively.Then, according to the reflectance formula, we present the concept and methods ofreflectance difference. And wavelength difference method is chosen to be the one thispaper adopts, comparing with other methods. Further analysis of system parameterchanging influence on wavelength difference method shows that: wavelength differencemethod is not sensitive to materials refraction index error, incident wavelength drift,incident angle change and film thickness change.Second, we build biosensor experimental system, using two wavelengths LEDlight to complete dual-wavelength difference experiment. The experimental resultsshow that: for4nm of SiO2layer, green light reflectance increases and blue lightreflectance decreases, while difference process eliminate the optical fieldinhomogeneity and sample surface roughness effects, which is agreed with thetheoretical analysis results; The method averaging multiple images summation removethe surface glitches of gray step caused by the shot noise, leading to more accurate andreliable quantification of the gray step height; Increasing optical system magnificationcan improve the image lateral resolution, and the use of RAW file can increase the graystep, raising the system sensitivity.Finally, according to the shortcomings of dual-wavelength difference method, weput forward the multi-wavelength method using the continuous spectrum light sourceand color camera. The theory foundation is analyzed from the aspects of color cameraimaging principle, sample reflection spectral characteristics and RGB signal layeredextraction. The experimental results, using a halogen lamp light, obtain a good matchwith the theoretical analysis that the reflectance of green signal increases in the singleimage pattern area, which is opposite to the red and blue signal. the experimental resultsshow that single image pattern area from the RGB three way signal, the green signalreflectance increases, the red light, blue light signal reflectance decreases, and the experimental results and the theoretical analysis, multi-wavelength difference methodimproves the image signal-to-noise ratio, solving the deviation problem ofdual-wavelength difference method which is competent for the qualitative analysis ofbiological reaction. Moreover, multi-wavelength difference method can further improvethe system sensitivity by attain higher gray step.