Study On SERS Detection Of Electric Field Regulation In Microfluidic Chip

Raman scattering spectroscopy is proverbial analytical tool based on the inelastic scattering of molecular photons,which provides information about the characteristic vibration,chemistry and structure of molecules.However,Raman scattering suffers from low scattering cross-sections,resulting in very low sensitivity.The key issue is solved by the surface enhanced Raman scattering(SERS)technique.Molecular Raman scattering cross-sections could be significantly amplified since analytes are adsorbed on SERS substrate(e.g.rough noble metals or transition metal surfaces).As an analytical tool to increase the intensity of Raman signals,surface enhanced Raman spectroscopy(SERS)has attracted wide attention among the public.Typically,the noble metal nanostructures(i.e.,Au,Ag,Cu)are active SERS materials to provide the enhancement for Raman signals.The SERS phenomenon is primarily a result of localized surface plasmon resonance(LSPR).LPRS is generated by the excitation of collective electron oscillations within the metallic nanostructure caused by incident light,which leads to a huge enhancement of the optical local-field on the nanoscale.Both theoretical and experimental studies have also demonstrated that electromagnetic hot spots for molecular detection can be formed by introducing plasmonic nanostructures or using SERS substrates inside microfluidic channels in nanoscale gaps between nanostructures.With ongoing progress in the development,the application of SERS has been extended to various fields,including biomedical detection and environmental safety,due to its ultra-sensitivity,rapid response time,and the ability to generate molecular vibrational fingerprint.Among these applications,SERS measurements coupled with microfluidic devices have emerged several useful benefits over conventional macro-environments.In the actual detection,by combining SERS with microfluidic devices,researchers can miniaturize their laboratory setup for SERS quantification,control the movement of particles in the channels,and decrease the assay time and procedures,which provides portability and lower production cost.Currently,in the research of SERS in microfluidics,most enhanced substrates consisted of metal nanostructure is directly fabricated in channel.Most methods are photoinduced synthesis,polyol heating,photoreduction and photothermal effects,and so on.However,it is difficult for the target molecules to reach the enhanced hot spots on the metal surface(≤ 100 nm)of enhanced substrates fabricated in channel,causing some difficulty for SERS detection.Therefore,many researchers adopt bonding methods to enable molecules to reach hot spots on the surface of metal structures,which form the simple bioconjugation and simultaneously realize detection of specific molecules.As a result,the SERS substrate might be hard to flush(e.g.presence of-HS groups)and ulteriorly bring significant disturbance to the subsequent SERS signal and analysis no matter for the same molecules or other molecules.It is negative for the extending of diverse applications.In other words,these SERS substrates are irreversible after chemical reaction or physical absorbance with analytes,limiting their recyclability.Considering the repeatability of SERS substrate,the researchers mixed metallic colloidal solutions and molecular solutions into microfluidic channels.However,the sensitivity of the substrate is relatively insufficient.Multiple reports show that the greatest enhancements come from specific hot spots generated by multiparticle coupling aggregation.Based on this idea,people promote the aggregation of nanoparticles to produce strong hot spots by dielectrophoresis(DEP).Therefore the combination of DEP-microfluidic and SERS offers unique advantages,opening up new opportunities in various research fields.In this work,a SERS detection in microfluidics with the help of the Ag nanowire aggregating based on dielectrophoresis(DEP)is reported.The Raman intensities of molecule in microfluidics is greatly enhanced in the naturally generated nanogaps of Ag nanowire aggregating modulated by DEP.Firstly,the influence of DEP voltage and time on Ag nanowire aggregating is investigated to figure out the optimal condition for SERS.And then,the SERS intensities of methylene blue and rhodamine6 G at various concentration with high reproducibility and uniformity are studied.Furthermore,the experiment data demonstrate this DEP-SERS system could be repeated used for different molecule detections.At last,the SERS of melamine in milk is measured to explore its application on food safety.Our work anticipates this nanowire assisted repeatable DEP-SERS detection in microfluidics with high sensitivity could meet the emerging needs in environmental pollution monitoring,food safety evaluation,and so on.