Study On SERS Detection In Microfluidic Chips

With the improvement of the level of micromachining technology,microfluidic chips have received more and more attention and have a wide range of applications in the fields of chemistry,physics,optics and biology.Because surface enhanced Raman scattering（SERS）technology shows its good characteristics in trace detection and biochemical molecular detection,the application of SERS detection technology in microfluidic chips has developed rapidly.SERS detection technology is based on the principle of localized electromagnetic field enhancement effect of metal nanostructures to perform ultra-sensitive spectral analysis of target molecules.Typical nanoparticles are gold,silver,copper,platinum,etc.These metals have optical absorption and scattering properties due to local surface plasmon resonances（LSPRs）.The combination of microfluidic device and SERS detection technology can achieve higher sensitivity,fast and convenient detection of target analytes.However,there are many research methods for preparing SERS substrates that are complicated,time-consuming and expensive.Therefore,this paper proposes three methods for preparing microfluidic chips,and characterizes the SERS substrate morphology,size and structural characteristics.First,a method for preparing a uniform substrate in a microfluidic chip is introduced using the polyol method and the heating method.Through the SEM image and the molecular SERS enhancement,the method of heating the silver precursor solution in the microfluidic channel for 8 minutes and heating the primary and secondary silver precursor solutions for 4 times was obtained to obtain the substrate with the strongest SERS signal.In addition,we use the time-domain finite difference method（FDTD）to briefly analyze the distribution of the dimer electric field of the particle size and particle spacing.At the same time,through SERS technology,we found that the substrate has good reproducibility for the Raman signal of the molecule.Finally,the detection limit of the prepared substrate for the methylene blue molecule is 1×10^-7M.The method can prepare a uniform silver nanoparticle active substrate in a microfluidic pipeline,and the preparation method is simple and convenient,and the cost is low.Secondly,we also used the replacement reaction method to prepare the silver nanoparticle active substrate on the copper sheet in the microfluidic chip.Through the SEM image and the molecular SERS enhancement,it was explored that the active substrate in the straight pipe can generate the highest Raman signal at a position 2 mm away from the entrance.The device has the ability to detect chemical molecules（such as MB）and biological molecules（such as urea）;at the same time,the device can also detect mercury ions in aqueous solution,and has good selectivity for mercury ions,the detection limit is 1×10^-7 M.In addition,we prepared a SERS substrate with a"Christmas tree"structure,and proved that the device can form an integrated concentration gradient microreactor and achieve SERS detection.This method does not require heating to prepare an active substrate,which takes less time,has lower cost,has a multifunctional substrate,and has a wide range of applications.Finally,we also propose a method for preparing three-dimensional Cu@Ag NPs SERS substrates by displacement reaction in microfluidic channels.It was verified by experiments that the Cu@Ag NPs structure substrate obtained when the 2 m M silver nitrate original solution was passed into the pipeline for 20 minutes could obtain the strongest SERS signal.In addition,it is also explored that laser is the best way to collect Raman signal from the glass surface of the microfluidic chip.The detection limit of the three-dimensional microfluidic sensor for chemical molecules MB is 1×10^-7 M.The device also has the ability to detect biological molecules such as urea and melamine.At the same time,the three-dimensional device not only has a SERS recognition effect on cancer cells but also serves as a simple filter.We have verified it with UV spectroscopy and optical microscopy.This method prepares SERS active substrate through replacement reaction,which is simple,time-consuming and low in cost.It can also be used as a simple micro-filter and has a wide range of applications in biochemistry.