Construction Of Novel SERS Nanoprobe And Its Application In Water Sensing And Chiral Amino Acid Detection

Surface-enhanced Raman scattering(SERS)has become popular in analysis and detection,especially in the detection of trace or even trace substances due to its high efficiency,non-destructive,portable,sensitive,and characterizable fingerprints.It has been widely used in biomedicine.,Environmental monitoring,food safety testing,material surface chemistry and many other fields.As the most effective substrate material for SERS enhanced detection,precious metal nanoparticles have also been widely studied.However,for substances with only weak Raman scattering and the same SERS signal,it is still necessary to design a specific detection substrate.In this study,water molecules and hand-shaped valine were used as the analysis and sensing objects,and two gel-modified SERS substrates were constructed:(1)Stimuli-responsive microgels with fluorescent and SERS activities for water sensing.Here,we have fabricated a dual-responsive platform capable of both sensitive on-spot fluorescence analysis and reliable surface-enhanced Raman scattering(SERS)quantification of water and temperature by in-situ encapsulating 4,4'-dimercaptoazobenzene(DMAB),meso-formyl-1,3,5,7-tetramethyl pyrromethene fluoroborate(FPF)probe and Ag nanoparticles(Ag NPs)into polyvinyl alcohol(PVA)microgels.Based on the linear relationship between the network volume change of the microgel and the SERS performance,the smart microgel exhibits an ultra-sensitive(detection limit of 10^-4%v/v)and reversible response to water.In addition,the presence of water triggers the conversion of FPF to aldehyde hydrate,which can facilitate the visual analysis of trace water in the matrix sample through the enhanced fluorescence signal.At the same time,the SERS signal can be precisely adjusted by the thermosensitive microgel matrix,so as to achieve temperature sensing from32 to 50^oC.The Ag NPs-DMAB-FPF microgel sensor can respond quickly and accurately to water in organic solvents and pharmaceuticals.As a smart and flexible sensor,hybrid microgels will promote the field of POC analysis and molecular recognition in the future.(2)Surface-enhanced Raman recognition of chiral valine based on Au NR@ZIF-8.In this work,we set up a machine to construct Au NR@ZIF-8 with gold nanorods(Au NRs)-modified by polyvinylpyrrolidone(PVP),encapsulated in an organometallic framework(ZIF-8)with a zeolite imidazole structure,which serves as an enhanced substrate for SERS response.The Schiff base effect of p-mercaptobenzaldehyde(4-FTP)and valine can accurately distinguish D/L-Valine chiral enantiomers.Compared with single bare Au NRs,Au NR@ZIF-8 base material shows better selectivity and stability based on its porous properties.The ratio of SERS characteristic peaks of 1634 cm^-1(C=N)and 1697 cm^-1(C=O)is used to characterize the response of 4-FTP to valine,I₁₆₃₄/I₁₆₉₇in D-Valine is greater than 1and L-Valine is less than 1,that is,4-FTP has a higher effect on D-Valine.At the same time,the SERS signal of D-Valine shows a rightward frequency shift trend relative to L-Valine at other characteristic peaks.Therefore,the analytical strategy proposed in this study can accurately distinguish chiral valine molecules and provide a new idea for the study of enantiomeric molecules.