Study Of Microfluidic SERS Chip Integrated With Nano-structure And Its Biochemical Application

The integration of optofluidic and microfluidic technology has become an important trend in the field of biochemical analysis based on microfluidic chip.Surface enhanced Raman spectroscopy(SERS)has the advantages of fast detection,no need for sample pretreatment,high sensitivity,ignorable influence from water background and so on.This technology could provide excellent properties of many detection methods,such as simplification of unmarked analysis,low detection limit of fluorescence detection,molecular feature identification of Raman spectrum.However,the qualitative and quantitative analyzing with the combination of SERS and microfluidic technology are still in their infant.In view of the bottleneck problems about current microfluidic SERS chip,such as limited SERS enhancement medium,poor repeatability,difficulty of chip integration,low sensitivity,non-reusable,Firstly,orderly nano gold substrates with tunable surface plasmon resonance were in-situ prepared in microchannels by using self-assembly chemical plating composite method.The preparation parameters of gold nanoparticles were determined by analyzing the structure-activity relationship between gold nanoparticles and the SERS enhancement effect.Secondly,a novel Au@Ag/TiO2 NTs composite SERS enhancement nanostructure was designed,and the synergistic SERS enhancement effect among different compositions were studied.Furthermore,the in-situ SERS detections of photocatalytic degradation process for diphenylamine(DPA)and Escherichia coli(E.coil)were realized.Thirdly,a novel microfluidic SERS detection microstructure which integrated with Teflon AF1600 liquid core waveguide(LCW)modified with nano gold was proposed,and the integration problem of gold nanoparticles,LCW and microfluidic channel was successfully solved.Moreover,the relationship between the structure parameters and the SERS enhancement effect was discussed in details.Finally,bovine serum albumin(BSA)was used as the test sample to verify the high effect SERS response on biosample.The main contributions of this work are listed as follows:(1)Based on the research status and development trend of the microfluidic SERS chip,the main problems on the current microfluidic SERS chip analysis system were point out.In this paper,Orderly Raman enhancement medium structures were integrated into microchannels by using a self-assembly-chemical plating composite method,and a novel SERS detection microstructure which integrated with Teflon AF1600 LCW modified with nano gold was designed and fabricated.The SERS detection sensitivity and repeatability could be further improved.Furthermore,the biochemical application study was developed,which laid a good foundation for further development of microfluidic SERS chips in the field of biochemical analysis.(2)Orderly nano gold within the microchannel was controllably prepared.Based on self-assembly chemical plating composition method,nano gold with different particle size was prepared by controlling the size of gold seed,distribution density and chemical plating time.The nano gold with average particle size of about 55 nm showed the maximum SSEF of 0.93×105,which indicated the prepared nano gold had excellent SERS activity.The influence of material and thickness of cover plate on microfluidic SERS detection efficiency was discussed.The results showed detection effiency could be increased to 68.8% under the PDMS cover plate thickness of 0.4mm.The problem of optical loss caused by the material and thickness of the cover sheet was effectively solved.(3)Design,fabrication,and SERS measures of Au@Ag/TiO2 NTs within the microchannel.Based on the self-assembly-chemical plating composite method,the density of gold seeds and silver shell thickness were effectively adjusted by controlling PDDA concentration and chemical silver plating time.Under the optimized conditions of gold core diameter of 18 nm and silver shell thickness of 3.5nm,the microfluidic SERS chip provided excellent enhancement effect for R6 G.The detection limit lowed to 10-10 M,and SERS enhancement factor(EF)reached to 1.15×108.Compared to single Au nanoparticles(NPs),Au@Ag NPs(Au core silver shell nanoparticles),Au@Ag/TiO2 plate,the SERS peak intensity of C-C-C bend(613 cm-1)of R6 G on the surface of optimized Au@Ag/TiO2 NTs was improved 20,2.3 and 1.6 times,respectively.The enhancement effect could be attributed to both electromagnetic and chemical enhancements.Otherwise,the microfluidic SERS chip could be reused for over six cycles through UV light photocatalytic purification.The photocatalytic degradation kinetic process of diphenylamine(DPA)and escherichia coli(E.coil)within the microfluidic SERS chips were in situ detection by using SERS.The first-order kinetic equation fits the experimental date well,and the Raman characteristic peaks of intermediate products could be observed.The reusable microfluidic SERS chip was realized.The application range of the microfluidic SERS chip was successfully extended to photocatalytic detection field.(4)A novel microfluidic chip with integrated Teflon AF1600 surface liquid core optical waveguide(LCW)modified with nano gold was proposed and fabricated.Physical deposition method was used to integrate Teflon AF1600 LCW into microchannel,and the Raman detection sensitivity for R6 G was improved by 2 orders of magnitude compared to before integration.After that,nano gold were in situ immobilized on the silanized inner surface of Teflon AF LCW that precoated with a thin layer of poly(diallyldimethylammonium chloride)(PDDA)by a chemical self-assembly method.The key technical problem of integration AF1600 LCW and nano gold into the microchannel was solved.The relationship among distribution density of nano gold,the microstructure length and SERS enhancement effect of the integrated microstructure were studied.It was found that the integrated microstructure was optimal for the 1.5cm-long integrated microstructure with coverage density of nano gold about 21 particles/um2.The detection limit lowed to 10-11 M for R6 G and SERS enhancement factor(EF)reached to 2.7 × 108.Compared to single nano gold substrate within a microchannel,the SERS detection sensitivity for R6 G was improved 4 orders of magnitude,and the enhancement factor was improved 3.9×103 times.The as-prepared integrated microstructure also had extremely good SERS detection reproducibility and duration stability.Furthermore,it was successfully used to detect BSA,and exhibited excellent SERS response.The research showed great prospects and technical support for design and fabrication of integrated microfluidic SERS chip and sensitive detection of trace biochemical samples.