Novel Nitrogen Doped Graphene-Based Electrochemical Sensors For Detection Of Pesticide Residue And Heavy Metal Ion

The development of sensitive, rapid, efficient and accurate detection method is the technical support for the implementation of national food safety plan. Meanwhile,it is of great significance to realize the social sustainable development and protect people's health. Owing to the advantages of low cost, simple instrument and rapid detection, electrochemical sensor has been widely used in food safety determination and become the research hot spot. While building electrochemical sensing interface is a critical step for developing high-performance electrochemical sensor. By coupling the electrochemical techniques such as electrochemical impedance spectroscopy (EIS),electrochemiluminescent (ECL), and photoelectrochemistry (PEC), herein, several electrochemical sensors have been successfully constructed for pesticide residue determination (such as acetamiprid and pentachlorophenol) and heavy metal iron detection (such as Pb2+) based on nitrogen doped graphene functional nanomaterials.The details were focused on :1. By employed nitrogen doped graphene/Ag (NGR/Ag) nanocomposites as the supporting materials, a novel photoelectrochemical (PEC) biosensing platform was developed for acetamiprid assay with the aids of acetamiprid aptamer. Due to the integrating the excellent electrical properties and large surface area of Ag NPs and NGR5 the obtained NGR/Ag nanocomposites show more effective electron transfer and high loading capacity. Under the optimal conditions, the presented PEC aptasensor exhibited a wide linear response for acetamiprid in the range of 1x10-13 to 5×10-9 mol L-1 with a low detection limit of 3.3x10-14 mol L-1 (S/N = 3). Moreover,this electrochemical aptasensor avoided complicated labeling procedures and showed magnificent sensitivity, high selectivity and low 'cost, which made it not only convenient but also time-saving and applicable.2. Nitrogen doped graphene quantum dots doped MoS2 nanosheets(NGQDS/MoS2) have been synthesized by a facile one-step solvothermal method. The introduction of NGQDs could improve the photoinduced carriers separation efficiency and benefit to suppress recombination of the electron-holes, resulting the enhanced PEC performances. Moreover, a novel label-free PEC aptasensor based on the"signal-off" system has been constructed for the sensitive and selective detection of acetamiprid with the aids of acetamiprid aptamer. This PEC sensing device showed a wide linear range (0.05 pmol L-1?1 nmol L-1),a low detection limit (16.7 fmol L-1,S/N = 3), high stability and detection reliability. This study not only offered an ingenious transducer for future uses in the broad PEC analytical field but also further understanding the charge separation mechanism in PEC biosensing, which opens up the possibility for designing more efficient PEC biosensors.3. A novel ZnO-nanocrystal-decorated nitrogen doped graphene composites(NGR/ZnO) were prepared through a one-step thermal-treatment route. The NGR/ZnO nanocomposites could not only enhance the electrochemiluminescence(ECL) intensity but also moved the ECL onset potential positively. All these results could be ascribed to the presence of nitrogen in graphene which decreased the barrier of ZnO nanocrystals reduction. Furthermore, the ECL sensor based on NGR/ZnO nanocomposites was fabricated for the ultrasensitive detection of pentachlorophenol(PCP). This recyclable and eco-friendly sensor has excellent performances including wide linear range (0.5 pmol L-1?61.1 nmol L-1),low detection limit (0.16 pmol L-1,S/N = 3), good selectivity, and stability, which is a promising sensor for practical application in environment analysis.4. A facile hydrothermal approach for cutting nitrogen-doped graphene into NGQDs has been proposed for the first time. The resulting NGQDs were homogeneously modified onto the surface of graphene oxide (GO) to form NGQDs-GO nanocomposites. Compared with NGQDs, the as-prepared NGQDs-GO nanocomposites exhibited excellent ECL performances including 3.8-fold enhancement of ECL intensity and a decrease by 200 mV of the ECL onset potential,which are ascribed to the introduction of GO. Based on the selective inhibitory effect of PCP on the ECL intensity of the NGQDs-GO system, a novel ECL sensor for PCP concentration determination was constructed,with a wide linear response ranging from 0.1 to 10 pg mL-1 and adetection limit of 0.03 pg mL-1. The practicability of the sensing platform in real water samples showed satisfactory results, which could open the possibility of using NGQDs-based nanocomposites in theelectroanalytical field.5. A novel nanocomposites consisting of TiO2 nanocrystals, Ag nanoparticles(NPs) and NGR via a facile one-pot hydrothermal route. The as-prepared ternary nanocomposites exhibited enhanced PEC performance owing to the introduction of Ag NPs and NGR, which increase the excitons' lifetime and improve the charge transfer. In particular, it is shown by means of the transient-state surface photocurrent responses that the photocurrent intensity of the as-fabricated composites exhibited 18.2 times higher than that of pristine TiO2. Based on the robust photocurrent signal, a new kind of "on-off-on" PEC aptasensor was established with the assistance of Pb2+aptamer, which integrates the advantages of low background signal and high sensitivity. Under optimal conditions, a wide linear response for Pb2+ detection was obtained from 1 pmol L-1 to 5 nmol L-1 as well as a detection limit down to 0.3 pmol L-1. With its simplicity, selectivity, and sensitivity, this proposed strategy shows great promise for Pb2+ detection in food analysis.6. AgBr nanoparticles anchored NGR composites were designed by a facile method and further applied in ECL sensing for the first time. Not only the stability of the AgBr NPs but also the intensity and stability of ECL emission from NGR/AgBr nanocomposites were markedly improved. Then a simple and cost effective ECL sensor based on NGR/AgBr nanocomposites was successfully fabricated for the detection of lead ions, demonstrating that it could be a novel class of efficient and promising luminophores for ECL sensing. The as-prepared ECL sensor has excellent performances including wide linear range (40 pmol L-1?6 nmol L-1),low detection limit (1.3 pmol L-1, S/N = 3), low cost and high selectivity. It could open a new avenue in the preparation of stable and strong ECL nanocomposite films for analytical applications.