Nanomaterials-based Regulation Of Electrochemical Sensing Property For Salmonella Surface Imprinting And Sensing Application

Non-typhoid Salmonella is one of the leading causes of foodborne illness,resulting in an increasing number of Salmonella infections across the country.Large numbers of people are infected and even killed by Salmonella each year to cause billions of dollars in lost productivity and medical care.Therefore,the rapid and simple detection of Salmonella is of great significance.At present,traditional culture detection methods,immunoassays,and polymerase chain reaction（PCR）are time-consuming and labor-intensive,while electrochemical sensing technology is widely used in food-borne pathogens due to its fast response,low cost,and high sensitivity.Recognition elements are the most important components of electrochemical sensing technology and common recognition elements are complex,expensive,and cannot be applied in complex environments.Therefore,bacteria imprinted polymers are used to prepare"artificial recognition elements".Although traditional imprinted methods are effective,efficient,and simple.But it also has some shortcomings:it is difficult to remove large target biomolecules（cells,bacteria and viruses,etc.）,which cannot penetrate into the polymer structure during the rebinding process,thereby destroying the biomolecular structure and resulted in low selectivity to target molecules.To overcome these problems,surface imprinted polymers are usually prepared by electrochemical methods.Polypyrrole（PPy）is a good conductive material and is often used as a functional monomer for bacterial imprinted electrochemical sensors.Nanomaterials have good dispersion and large specific surface area.Therefore,the doping of nanomaterials can not only change the microstructure of polypyrrole,but also affect the interaction between the pyrrole monomer and the template bacteria,thereby regulating the sensing performance of surface imprinting.In this thesis,three types of surface-imprinted electrochemical sensors for Salmonella were constructed using pyrrole as the functional monomer and carbon nanotubes,MXene and molybdenum disulfide（Mo S₂）as nano-regulators.The main contents are as follows:（1）The Salmonella,pyrrole,and single-walled carbon nanotube（SWNT）dispersions were subjected to one-step electrochemical polymerization,and then soaked in an eluent to remove the Salmonella template to construct the SWNT/PPy-based bacteria imprinted polymer（SPBIP）sensor.The electrochemical polymerization adopts cyclic voltammetry,and the thickness of the bacteria imprinted polymer can be controlled by parameters such as scanning speed,scanning number of turns,and potential.At the same time,the conditions affecting the sensor are optimized.Template bacteria are removed from the surface of the polymer matrix,resulting in specific"non-hole"bacteria surface imprinted sites that are more easily recognized Salmonella.The sensor only needs 40 min to remove the Salmonella template,only needs to incubate for 50 min to detect Salmonella and has a wide detection range of 10¹-10⁷ CFU/m L.（2）MXene Ti₃C₂T_X was used as a nano-regulator to polymerize with pyrrole monomer and Salmonella template on the surface of glassy carbon electrode by cyclic voltammetry,then soaked in eluent to remove Salmonella template to prepare MXene/PPy-based bacteria imprinted polymer（MPBIP）sensor.Compared with the PPy-based bacteria imprinted polymer（PBIP）sensor,MPBIP greatly shortens the elution time（5 min）and the recognition time（1 h）.In addition,several conditions affecting the detection performance of the sensor,such as the concentration of MXene,the polymerization period,and the eluent,were studied and optimized.Electrochemical impedance spectroscopy（EIS）for label-free detection of Salmonella.Under optimal experimental conditions,the Salmonella template was substantially removed from the electrode surface,and the relative change in electron transfer resistance（ΔR/R）was linearly related to the logarithmic concentration of Salmonella.The MPBIP sensor has a detection limit of 23 CFU/m L,high sensitivity,and good selectivity.Besides,the prepared MPBIP electrochemical sensor can be reused at least 3 times and can be successfully applied to the detection of Salmonella in real samples.（3）Using molybdenum disulfide as a nano-regulator,a molybdenum disulfide-regulated polypyrrole was constructed to prepare a surface-imprinted sensor for Salmonella.The Salmonella,pyrrole,and molybdenum disulfide dispersions were subjected to one-step electrochemical polymerization,followed by soaking in an eluent to remove the Salmonella template to construct a Mo S₂/PPy-based bacteria surface imprinted polymer（MBSIP）sensor.In addition,the conditions affecting the performance of the sensor were optimized,the optimal template removal time was 40 min,the Salmonella template could be completely removed from the surface of the polymer matrix,and the imprinted sites on the surface of bacteria formed"non-hole"that could specifically recognize Salmonella and recognition time was 30 min.The sensor has a wide detection range with a limit of detection of 3 CFU/m L,has good stability,and can be stored for 5 weeks.And it can detect Salmonella in drinking water and orange juice samples,which has certain application prospects.