Detection Of Sulfonamides And Quinolones By Surface-Enhanced Raman Spectroscopy

Antibiotics are widely used in the medical field because of their excellent antibacterial ability.In the early years,due to the inadequate supervision of the use of antibiotics,the abuse of antibiotics led to the emergence of drug-resistant bacteria,which posed a huge potential threat to the ecological environment system and human health.Therefore,in recent years,the rational use and effective control of antibiotics have attracted much attention,and reliable detection technology is needed to realize the qualitative and quantitative analysis of antibiotics.In order to meet the needs of emergency monitoring,the development of reliable on-site rapid detection technology has also been put on the agenda.With the advent of portable Raman spectrometers,Surface-Enhanced Raman Spectroscopy(SERS)with near-single-molecule level high sensitivity and high-resolution molecular fingerprints can be an efficient method of rapid detection.In this article,two typical antibiotics,sulfonamides and quinolones,are used as the research objects,and the feasibility of SERS technology detecting trace amounts of antibiotics is discussed:1.Research on the detection of trace sulfa antibioticsThree sulfa antibiotics(sulfadiazine,sulfamerazine and sulfamethazine)are used as target molecule s to systematically study the influence of the pH value of the solution,substrate,and agglomerating agent for the selectivity and sensitivity detection of sulfa antibiotics.(1)The role of pH value in the solution:Affect the electrical properties of molecule,spatial structure and photochemical reactions.Under strongly acidic conditions,the spatial structure of sulfadiazine is folded,and its adsorption on the surface of the substrate is weak;under strong alkaline conditions,sulfadiazine will undergo LSPRinduced photochemical reactions to generate azo compounds;the characteristics of the sulfadiazine can be maintained under neutral conditions,which is conducive to SERS detection.(2)The role of agglomerating agent:For positively charged target molecules,anions with appropriate adsorption capacity can induce the target molecules to be coadsorbed on the surface of the SERS enhanced substrate,which can be highly sensitively detected.If its adsorption capacity is weak,anions will not be able to induce the co-adsorption of molecules on SERS enhanced substrate.If its adsorption capacity is too strong,it will prevent the target molecule from directly adsorbing on the surface of the SERS enhanced substrate,thus failing to generate the SERS signal.On the one hand,cations can induce agglomeration and form SERS hot spots.On the other hand,the specific adsorption on the surface and the steric hindrance effect will hinder the SERS detection of the target molecule.Only the mutual "trade-off" of the anion,cation and the molecule can achieve the maximum enhancement of the SERS signal.2.Research on the detection of trace quinolone antibioticsBased on proposed a co-adsorption mechanism of agglomerating agent,target molecule and SERS enhanced substrate in the research of highly sensitive detection of trace amounts of sulfonamide antibiotics,the qualitative and quantitative research of 16 quinolone antibiotics is systematically carried out.(1)Qualitative analysis:The Raman shift of the SERS spectra of molecules with large structural differences(such as pipemidic acid and rosoxacin)are significantly different and easy to distinguish;analysis can also be achieved for molecules with smaller differences(such as ciprofloxacin and enrofloxacin,etc.),although their main characteristic peaks in the SERS spectra are small,the peak position of other position characteristics is still different;for molecules with only chiral differences(such as ofloxacin and levofloxacin),the SERS spectra are almost the same,and it is still necessary to develop chiral SERS technology for detection and identification.(2)The influence of SERS enhanced substrate and agglomerating agent on SERS detection sensitivity:With the Ag NPs as SERS enhanced substrate and NaI as agglomerating agent,the best detection sensitivity is obtained.One of the reasons is that Na+destroys the dual layer of the Ag NPs colloid to generate "hot-spots",and there is no strong specific adsorption,so Na+is suitable for cation;I’appropriate adsorption on the SERS enhanced substrate can make more target molecules adsorbed on the surface of the substrate,and the three "trade-off" make the SERS signal stronger.(3)The influence of molecular structure on detection sensitivity of SERS:The structural difference of quinolone molecules will change the interaction between the molecule and the SERS enhanced substrate,which changes the SERS detection sensitivity(with fluctuations between 0.1 and 1 μg/L).The methods to improve the sensitivity of molecular detection include:1)Making the piperazinyl group(or pyrrolidinyl group)exist in the structure of primary or secondary amine,especially primary amines,and its complexation can improve molecule’s adsorption to SERS enhanced substrate;2)By modified a cyclopropyl,fluorophenyl or other groups on the quinolone 1 position,the positive electrical properties of the N are increased,which enhance the adsorption of molecules to negative electrical substrates;3)The adsorption of the molecule to the SERS enhanced substrate can be improved by reducing the number of alkyl in N on the piperazinyl group.