Study Of The Double SERS Substrate Chip Based On A Liquid Core Waveguide

It is of great importance to conduct a rapid, accurate and non-destructive testing of bacteria, virus, DNA and living cells in research field of the life science. Surface-enhanced Raman Spectroscopy(SERS) technique has the characteristics of fast detection speed, samples label-free, and high detection sensitivity etc. As SERS can reveal the internal structure information of a sample molecule, it has been an important analysis tool in the life science. SERS chip combines SERS with micro-fluidic technique. Combining with a small size of micro-fluidic channel, SERS chip can be applied to detect trace amounts and low concentration samples. However, conventional SERS chip suffers the drawbacks of large power density of excitation light, poor repeatability, and low level of integration, hence it is difficult to satisfy the demand of biological sample analysis. To overcome the problem, we propose a SERS chip integrated by a liquid-core waveguide(LCW), SERS substrate and inlet/outlet channel. The Raman signal of sample is enhanced by reducing the loss coefficient of LCW to increase the optical path between light and sample molecule. And the Raman signal repeatability is improved by the averaging effect of liquid flow. Eventually an integrated SERS chip with low power density of excitation light, low loss coefficient, high enhancement and excellent repeatability is accomplished. It lays the foundation of quantitative analysis of biological samples.This thesis mainly focuses on the theory, design, manufacture and test application of the LCW SERS chip. The content is mainly as follows:(1) We establish the theoretical model of liquid-core waveguide transmission SERS signals, discussing the local field enhancement coefficient of liquid-core waveguide influenced by the material properties, geometrical structure of metal particles, particle size, and distribution density etc. Transfer matrix method is applied to analyze the loss characteristics of the symmetry liquid core waveguide. We study the relationship between the output SERS signal intensity and the loss coefficient of the liquid-core waveguide. Results show that SERS chip can perform the largest local field enhancement factor with Ag nanoparticle diameter of 50 nm, and distribution density of 11 particles/?m2. The optimum chip length is about 0.7 times of the reciprocal of the loss coefficient. When Ag nanoparticles in SERS chip distribute randomly, the signal repeatability of forward scattering is better than backward scattering.(2) We propose two type SERS chips which are non-total reflection liquid-core waveguide SERS chip and total reflection LCW SERS chip. We optimize the coating material, thickness, geometry of LCW, configuration of SERS substrate etc. We found that the loss coefficient is 2×10-3 cm-1 while adopting the non-total reflection liquid-core waveguide with the gold film thickness of 100 nm, and the width of 100 ?m. Total reflection liquid-core waveguide coated with the Teflon AF 2400 of thickness larger than 5 ?m can support liquid-core waveguide total reflection condition. When the diameters of waveguide are larger than 400 ?m, loss coefficient is 1.457×10-3 cm-1. The double SERS substrate, the waveguide wall and the liquid core that both were distributed with silver particles can obtain the biggest enhancement factor of 86.3.(3) We study the processing technique of LCW SERS chip and optimize the technological parameter of two type SERS chips. The non-total reflection liquid-core waveguide SERS chip is fabricated by the monocrystalline silicon. A wet etching method is used to form channel on the silicon, then the cover plates and substrate channel are magnetron sputtered with 100 nm gold film as the reflector. The cover plates and substrate channel are glued together, and the mixed silver sol and the detection solution are added into the liquid core waveguide, forming a non-total reflection liquid-core waveguide SERS chips. Total reflection liquid-core waveguide SERS chips are fabricated on the flexible polymer PDMS, and the microfilament modeling method is adopted to form a circle micro-channel. Then low refractive index material AF 2400 is coated on the inner of the micro-channel. Finally, silver sol is deposited on the waveguide wall and injected into the liquid core to form total reflection liquid-core waveguide SERS chip. The characterization show that the loss coefficient of the non-total reflection liquid core waveguide SERS chip is 3.1 cm-1,and the loss coefficient of the total reflection liquid core waveguide SERS chip is 1.1 cm-1.(4) We test the performance of the liquid-core waveguide SERS chip. In order to detect Raman signals of SERS chip with long-range, we built a transmission type SERS test system,and test the key parameters of SERS chip, such as, the enhancement and repeatability, by using a portable Raman spectrometer. Results show that the optimum length of the non-total reflection SERS chip is 2 mm and total reflection SERS chip is 7 mm, which are consistent with the theoretical analysis. 10 n M R6 G solution is detected by total reflection liquid-core waveguide SERS chip at 3.63 W/cm2 power intensity of excited light. The Raman signal intensity of 10 n M R6 G solution is tripled compared with that is detected by non-total reflection liquid-core waveguide SERS chip at 132 W/cm2 power intensity of excited light. The Raman enhancement factor of the total reflection liquid-core waveguide SERS chips is 2.5×105 and the repeatability of RSD is 14.74%.(5) The total reflection liquid-core waveguide SERS chip is tested with bio-molecular of 5 x 10-7 M Adenine solution and 3?L(concentration of 25?g/m L) silkworm DNA solution with a clear and sharp Raman peaks.Our results demonstrate a low loss and power density of excitation light, as well as high enhancement of the developed total reflection SERS chips. Compared with the conventional SERS chips, total reflective liquid-core waveguide SERS chip has the similar limit of detection, however, it decreases the power density of excitation light by nearly 4 orders of magnitude. Our experimental results show that total reflection liquid-core waveguide SERS chip is more suitable for the detection of the trace amounts and low concentration biological sample.