The Applications Of Nitrogen-doped Graphene Quantum Dots-based Fluorescence And Electrochemiluminescence Nanosensors

In recent years,carbon-based luminescence nanomaterials have received research attention due to their unique optical and electronic properties.Graphene quantum dots?GQDs?,as a novel type of carbon nanomaterial,possess various merits,such as high optical stability,versatile surface modification,high surface area,low toxicity and unique electron transportation properties.Doping graphene quantum dots with N atoms can modulate the band gap of GQDs and tune electronic characteristics,local chemical properties and optical properties,then extended the application range in the fluorescence and electrochemiluminescence nanosensors.In this article,we have developed fluorescence nanosensors for the detection of sulfite and picric acid by the modulated photoluminescence of nitrogen-doped graphene quantum dots?N-GQDs?,a novel electrochemiluminescence nanosensor for nitroaniline,and a highly selective determination method of Escherichia coli O157: H7 based on the polydopamine surface imprinted polymer and the electrochemiluminescence property of N-GQDs.In chapter 1,we introduced the synthesis methods and optical properties of GQDs,and the development and application of N-GQDs.In chapter 2,we established a fluorescence nano-probe for sulfite sensing based on the fabricated N-GQDs.Due to the high quenching efficiency and selectivity of Fe³⁺ on the N-GQDs and the redox reaction between Fe³⁺ and SO₃^2-,we developed a fluorescence “turn-off-on” sensing mechanism and detected sulfite in waters.In chapter 3,we assembled a creatinine capped chitosan-N-GQDs solid film on the silica slides and developed a nanosensor for picric acid.Jaffé reaction between creatinine and picric acid can make the solid film absorb picric acid selectivity,then electrons can be transferred from the N-GQDs to electrophilic picric acid and leadingto the fluorescence signal decrease of solid film.Picric acid can be quantitative detected by the changed signal.In chapter 4,a facile novel electrochemiluminescence signal-on method for nitroaniline sensing was developed based on N-GQDs and chitosan.N-GQDs have shown as highly active reagent and catalyst for rapid diazotization reaction of anilines.When NA was added to the electrolyte solution consisting of mineral acid and sodiumnitrite,N-GQDs/chitosan modified electrode exhibited obvious enhancement of ECL intensity,which was ascribed to the occurrence of diazotization reaction of NA.Therefore,NA can be detected with high selectivity based on the N-GQDs/chitosan electrochemiluminescence system.In chapter 5,Escherichia coli O157: H7 polydopamine surface imprinted polymer?PDA SIP?was established on the electrode surface through the electropolymerization method.Due to the complementary shape and size between the formed PDA SIP and the template Escherichia coli O157: H7,PDA SIP can capture Escherichia coli O157: H7 highly selectively.Meanwhile,we labeled the polyclonal antibody?p Ab?with N-GQDs and obtained the p Ab-N-GQDs.The bioconjugation in SIP-Escherichia coli O157: H7/p Ab-N-GQDs can generate ECL with the reactant.Then Escherichia coli O157: H7 can be detected by the enhanced ECL.