The Fabrication And Application Of Photoelectrochemical Sensor Platform For The Detection Of Foodborne Pathogenic Bacteria

Foodborne pathogens contamination is the most serious problem in global food safety.Food products can be contaminated by a variety of foodborne pathogens in production,processing,transportation,storage,and distribution.Therefore,it is critical to establish a rapid,sensitive,and portable detection method to achieve on-site detection of foodborne pathogens.Photoelectrochemical（PEC）,developed on the basis of photochemistry and electrochemistry,is a new detection method which has the advantages of low background signal,high sensitivity and easy simplification of the device,thus has good prospects for application in the field of food safety detection.In this thesis,three novel PEC sensors were constructed based on reduced graphene oxide（r GO）-sensitized MoS₂ nanosheets（GMS）,Bi₂S₃ and Cu₂O as the photoelectric signal materials,through molecular recognition of antibodies,aptamers and DNA and biomagnification,combined with paper-based electrodes and portable photoelectric detection devices,to achieve the rapid and highly sensitive detection of Escherichia coli O157:H7（E.coli O157:H7）and Staphylococcus aureus（S.aureus）.The research of the thesis mainly includes:（1）GMS with good photoelectric conversion performance was designed and prepared,and used to construct a sandwich-type PEC immunosensing platform for the rapid and sensitive detection of E.coli O157:H7.Firstly,the in situ growth method was used to obtain the GMS sheet,and the PEC performance of GMS was improved due to the good conductivity of r GO to promote the migration of MoS₂ photogenerated carriers.Meanwhile,a magnetic screen-printed paper-based electrode（MSPPE）was used to immobilize magnetic nanoparticles（MNPs）modified with anti-E.coli O157:H7 mouse monoclonal antibodies（MAb₁）,denoted as MNPs-MAb₁,after capturing E.coli O157:H7 specifically,the bound E.coli O157:H7 reacts with GMS sheets modified with anti-E.coli O157:H7 rabbit polyclonal antibodies（GMS-PAb₂）,resulting in the formation of sandwich-type immunocomplex.The photoelectric properties of GMS driven by near-infrared（NIR）light,the modification process of GMS on the electrode and the PEC response of E.coli O157:H7 were investigated in detail.As the result,the linear range of the sensing platform for the detection of E.coli O157:H7 was 5.0～5.0×10⁶ CFU m L^-1,and the detection limit was 2.0 CFU m L^-1.The established method was directly applied to the quantitative analysis of E.coli O157:H7 in milk,and the results were in high agreement with the plate count method The results were in high agreement with the plate count method.（2）Based on the above study,a portable PEC biosensor with target-induced photocurrent polarity switching was developed by changing the photogenerated carrier migration path of GMS using a mismatched energy band matching scheme.Firstly,GMS was immobilized on the surface of a commercial screen-printed electrode（SPE）and attached to a hairpin（Hp）containing G-quadruplex by a classical amidation reaction,at that time,the modified electrode responded with anodic photocurrent under NIR light excitation.Next,the Hp containing G-quadruplex was induced to turn on using E.coli O157:H7,exposing the binding site with hemin,forming the G-quadruplex/Hemin structure,and changing the photogenerated carrier migration path of GMS by Hemin,thus inducing the photocurrent polarity switch to cathode.Meanwhile,the G-quadruplex/Hemin forms a DNAzyme that could assist in enhancing the PEC signal after the switchover.The portable PEC sensor for E.coli O157:H7 detection was finally constructed through detailed characterization of the construction process,research on the mechanism of photocurrent polarity switching,and optimization of detection conditions.The sensor has excellent anti-interference performance,wide detection range(25.0～1.0×10⁷ CFU m L^-1)and low detection limit(2.0 CFU m L^-1),and has been successfully applied to the detection of artificially contaminated E.coli O157:H7 in milk.（3）A dual-channel portable PEC biosensor was developed for the rapid and sensitive detection of E.coli O157:H7 and S.aureus using B_i2S₃ and Cu₂O as photoelectric beacons in combination with recombinase polymerase amplification（RPA）.Firstly,two working surfaces were designed on screen-printed paper-based electrodes（SPPE）to immobilize the forward primers of E.coli O157:H7 and S.aureus,respectively.After that,the relevant genomic DNA（g DNA）was added dropwise on the corresponding electrode surfaces to initiate RPA,and the quantitative detection of target pathogens were achieved by forming DNA-PEC beacons.Bi₂S₃ and Cu₂O were used as photoelectric beacons,which not only have strong photoelectric activity,but also have opposite photocurrent directions and do not interfere with each other’s signals.The linear ranges of the constructed sensors were 10.0～1.0×10¹⁰ and 10.0～1.0×10⁷ copiesμL^-1 for E.coli O157:H7 and S.aureus,respectively,with detection limits of 3.0 and 7.0 copiesμL^-1,respectively.