| Microfluidic chips are experimental devices that integrate chemical andbiological analytical processes, including the synthesis, reaction, separation anddetection onto one single microchip and complete the analysis. Microfluidic chipshave received extensive attention since1990‘s in biology, chemistry and medicine.Microfluidic chips have undergone a history from incipient simple functions tosophisticated biomimic applications. With the development of microfluidic chips,more and more analysis methods have been applied in the detection of analytes, forexample, electrochemistry,also optics, which includes refractometry, fluorescence,uv-vis absorption, chemiluminescence and Raman spectroscopy. Surface-enhancedRaman spectroscopy (SERS) has also been widely applied in the detection of amicrofluidic chip in the recent decade. This is because SERS is not just a qualitativefingerprint spectroscopy method, but also advantageous in sensitivity andreproducibility, and non-contact detection. Combined with microfluidics, SERSmethod can demonstrate its unique advantage: small laser spot which enables thefocusing of detecting beams into the microchannels directly; high sensitivity whichmeets the demand of low volume detection of microfluidics; non-contact detectionability which has leads to no interference to the analyte system; rich spectrumfingerprint which allows the mixing and precise recognition of several analytes.Theenhancement performance of SERS is mainly due to the concentrated electromagnetic field around plasmonics nanoparticles, and the field that is bound inthe gap of the nanoparticles, i.e. localized surface plasmon resonance (LSPR).Therefore, the reproducibility and ordered structure of the SERS substrate can bedirectly influencing the performance of SERS enhancement, which means thefabrication of a high-performance SERS substrate in a microfluidic channel isnecessary. This dissertation studies the preparation of high-sensitivity and highlyreproducible SERS enhancement substrate in microfluidic channels, which is dividedinto following three chapters:1.Fabrication of Silver nanodot arrays SERS substrate by anodic aluminumoxide (AAO) templateWe exploited the conventional two-step method to fabricate an ultrathin anodicaluminum oxide (AAO) film as an evaporation mask for the successful fabrication ofa patterned silver nanodot array. The effect of pore-widening time for AAO film onthe morphology of resulting silver nanodot array was studied. The influence of thethickness of the nanodot on the SERS performance of enhancement was studied withthe sensitivity and reproducibility. A finite difference time domain(FDTD) numericalsimulation was used to verify that the gap between20nm is a critical factordetermining the construction of SERS―hotspts―, which was in agreement withconventional theory of nanoparticle-enhanced SERS effect.2.Fabrication and study of PDMS/Quartz microfluidics chips with Agnanodot arrays SERS substrateWe used a quartz substrate with silver nanodot arrays with channel-replicatedPDMS film as a cover combined to produce a microfluidic chip that is able to detectpollutant small molecules. With the integration of a home-made microfluidicanalyzer, we are able to analyze the thiram and adenine molecules adsorbed onto thesilver nanodot arrays in the micro-channels. The interference of the PDMS cover tothe SERS signals was studied, demonstrating the advantage of the analyzer in theapplication of a microfluidic chip, by which we are able to prove that themicrofluidic chip embedded with plasmonics silver nanodot arrays can be applied inpollutant recognition and biomolecular labeling. 3.Study of in-situ photo-polymerization porous materials assembles with Aunanoparticles as SERS active substrateGMA-SR454porous material was in-situ polymerized by a light-induced method,and gold nanoparticles were bonded with the porous material by cysteamine whichprovides surface thiol groups, forming a uniform monolayer of gold nanoparticles asa SERS-active substrate. Since the gold nanoparticles are bonded to porous materialswhich have big surface areas, giving them the ability of adsorbing more analytes, theSERS substrate we fabricated has good SERS enhancement performance. Under anintegration time of4s, the limit of detection for4mpy can be as low as1.0×10-8M.Due to the influence of the gaps of porous microspheres to the assembly of goldnanoparticles, we investigated the best structure of the composite material bychanging difference ratios of monomer, linker and pore-opener mixture, and in themeantime we studied the light-inducing duration‘s influence on the synthesis ofporous materials. Then difference diameters of gold nanoparticles were synthesizedto be assembled with4-mpy molecules, by which we can check the SERSperformance. Solutions with difference pH values were injected in the quartzcapillary to compare the protonization peaks of4-mpy in order to demonstrate thechange of pH. |
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