Fabrication Of Electrochemical Sensors For Determination Of Hydroxylated Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbon(PAHs) is a persistent organic pollutant(POPs) which has potential teratogenic, carcinogenic and mutagenic effects and widely distributed in the environment and food. Dietary intake is also the most important ways of human exposure to PAHs except breathing and skin intake. The PAHs intake in human body can be assessed through the determination of PAHs exposure biomarkers-hydroxylated polycyclic aromatic hydrocarbon(OH-PAHs) in urine, which can provide reference for human PAHs intake levels, adjust the way of daily diet, and improve the level of human health. Electrochemical method is easy to operate and realize miniaturization, able to meet the needs of modern analysis for fast and efficient. However, simultaneous electrochemical approach of detecting OH-PAHs is still in its infancy, and the target is only for 1-hydroxypyrene or naphthol analysis. In this paper, we committed to fabricate electrochemical sensors using water-soluble quantum dots, graphene oxide and benzene/carbazole polyelectrolyte respectively on basis of quantum-dots(QDs) electrochemiluminescence(ECL) technique and electrochemical accumulation and sensing in situ to sensitively detect OH-PAHs. The details are shown as follows:(1) An ECL sensor was designed for sensitive detection of 1-OHPyr by covalently immobilizing CdTe/CdS/ZnS QDs on p-aminobenzoic acid modified GCE with ethylenediamine as a link molecule. The fluorescence spectrum were used for characterizing CdTe/CdS/ZnS QDs, indicating that QDs kept their good light emission features after being immobilized. It is confirmed that the addition of 1-OHPyr has fluorescence quenching effect on the the reaction system between quantum dots and(NH4)2S2O8.To ensure sensitivity and effectiveness of this method, 2.0 μmol/L quantum dots, scan speed under 50 mV/s and pH 7.4 were chosen respectively. Under the optimal conditions, linear responses were obtained between the relative ECL intensity and the concentration of 1-OHPyr ranged from 200 nmol/L to 800 nmol/L, with limits of detection of 10.1 nmol/L, 15.3 nmol/L, 20.4 nmol/L(S/N=3). Finally, it was successfully applied in real human urine samples with recoveries of 83.9%~104.7%, results of determination were similar to HPLC method.(2) A new simultaneous electrochemical approach was developed for the accumulation and in situ detection of 1-hyroxypyrene(1-OHPyr), 3-phenanthrol(3-OHPhe) and 2-naphthol(2-OHNap). Firstly, electro-reduced grapheme oxide(E-rGO) was directly deposited on Screen-printed electrode, and the preconcentration of targets was enriched by π-π conjugate accumulation. It has found that the oxidation of 1-OHPyr, 3-OHPhe and 2-OHNap occurs respectively at potentials of +0.091 V, +0.323 V and +0.535 V by differential pulse voltammetry(DPV). Secondly, the optimal conditions of 1-OHPyr, 3-OHPhe and 2-OHNap detection were 350 s for GO electrochemical-reduced time, pH 4.0 PBS, 40 min for preconcentrate time. Under the optimal conditions, linear responses were obtained between the oxidation current of 1-OHPyr, 3-OHPhe and 2-OHNap and the concentration ranged from, 100 nmol/L to 1000 nmol/L, 50 nmol/L to 1150 nmol/L, 50 nmol/L to 800 nmol/L respectively, with limits of detection of 20.4 nmol/L, 15.3 nmol/L, 10.1 nmol/L(S/N=3). The method exhibited good stability and antidisturbance ability. Finally, it was successfully applied in real human urine samples with recoveries of 95.1%~98.9%, 92.5%~104.9%, 87.5%~101.7%, which were similar to the datas of HPLC method.(3) The {GR-PPC}n modified glassy carbon electrode({GR-PPC}n/GCE) was prepared by layer-by-layer(LBL) self-assembly of grapheme(GR) and Benzene/carbazole polyelectrolyte(PPC) through π-π conjugate action. The UV-vis spectroscopy and cyclic voltammetry were used for characterizing {GR-PPC}n, confirming that the LBL self-assembly process of {GR-PPC}n was uniform and controllable. When detecting the mixtures of 1-OHPyr, 3-OHPhe and 2-OHNap at {GR-PPC}n/GCE, three well-defined sharp oxidation peaks representing 1-OHPyr, 3-OHPhe and 2-OHNap were presented with peak potentials +0.091 V, +0.361 V, +0.573 V. The optimal conditions for detection conditions at {GR-PPC }n /GCE were 0.6 mg/mL for PPC-SO3 Na solution, 0.5 mg/m L for PPC, 6 for layer number, pH 4.0 for PBS, 30 min for accumulation time. Good linear relationships between the concentrations of 1-OHPyr, 3-OHPhe and 2-OHNap and corresponding DPV response currents were obtained in the range of 20~160 nmol/L, 10~160 nmol/L and 10~140 nmol/L with detection limits(S/N=3) of 10.4 nmol/L, 2.31 nmol/L, and 1.43 nmol/L respectively. When the method was applied for the detection of 1-OHPyr, 3-OHPhe and 2-OHNap in real human urine, results were similar to HPLC method. For the easy operation and satisfactory results, {GR-PPC}6/GCE may be an excellent alternative simultaneous electrochemical determination for OH-PAHs in urine sample.