Direct Sers Detection Of Liquid And Gas Pollutants Based On Capillary

Surface-enhanced Raman Scattering Spectroscopy（SERS）,as a non-invasive,high-sensitivity,molecular fingerprinting technique,has emerged as a powerful and promising analytical technique with a wide range of applications in food inspection,medical diagnosis,and environmental monitoring.Gold or silver nanoparticles are usually assembled on the substrate to form a two-dimensional planar SERS substrate,but there has always been a problem in controlling the uniformity of the hot spot at low cost,and it is difficult for the liquid or gas phase trace target molecules to enter the hot spot area,which greatly limited its application.The three-dimensional SERS substrate greatly prolongs the interaction distance between the laser and the analyte.While spatial accumulation enhances the Raman signal,it also reduces the requirement for the homogeneity of the hot spot.It is an ideal choice for the detection of trace molecules in the liquid or gas phase.Among them,capillary stands out from many three-dimensional substrates due to it excellent characteristics such as convenient sampling,flexibility,and low cost.In this paper,a SERS-active capillary substrate is developed for ultrasensitive SERS detection of liquids and gases.The specific research contents are as follows:1.A method of premixing gold nanoparticles（Au NPs）with the molecules to be tested is proposed to form SERS active capillaries.By controlling the size of Au NPs and excitation laser to form localized surface plasmon resonance（LSPR）,the crystal violet（CV）aqueous solution can be achieved as low as The detection of 10^-9 M,the enhancement factor is as high as 10⁸,the SERS signal of the end surface near the inner wall of the capillary air channel is uniform,and the relative standard deviation is less than 15%,which has high sensitivity and greatly reduces the difficulty of operation.2.The capillary has a larger diameter of the microfluidic channel,which is beneficial to the coupling of the laser and the injection of the liquid.However,the capillary only supports leakage mode,and high SERS sensitivity can be achieved only when the laser is grazing incident on the inner wall of the microfluidic channel,and the SERS signal will drop sharply when the laser deviates from the inner wall.In Chapter3,a refocusing light feedback mechanism is proposed.By coating the outer wall of the capillary with a silver film,the low concentration detection of rhodamine 6G（R6G）aqueous solution is realized.The detection limit reaches 10^-10 M,and The SERS signal is uniform across the entire end face of the capillary microfluidic channel（70μm）.The relative standard deviation is less than 7%,which has good repeatability and greatly reduces the difficulty of laser coupling alignment.3.Capillary liquid detection has better effect by using enhanced nanoparticle premixing with the molecule to be measured,but this method is often impossible for gaseous molecules to be measured.Chapter 4 proposes a method to form high-density hot spots and adsorption regions on the inner surface of the capillary.By adding Au NPs to the reducing agent of the silver mirror reaction,the highly dense growth of silver nanoparticles（Ag NPs）on the inner wall of the capillary is regulated,and the carbon dioxide is realized.The detection of nitrogen（NO₂）and carbon monoxide（CO）gases as low as 1 ppm can be extended to the actual vehicle exhaust gas detection.The sensitivity is good and the Raman characteristic peaks are easy to distinguish.It is suitable for rapid on-site detection and has a wide range of practical value.