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A simple and sensitive label-free electrochemical biosensor for nimodipine was fabricated by using nitrogen-doped graphene (NGE) modified electrode. The surface morphology and electron transfer behavior of the modified electrodes were studied by scanning electron microscopy and electrochemical impedance spectroscopy, respectively. The electrochemical behaviors of nimodipine at the modified electrodes were investigated by using cyclic voltammetry. On the basis of the excellent electrocatalytic activity of NGE, an obvious cathodic peak of nimodipine could be caused at the NGE modified glassy carbon electrode (GCE), moreover, the electrochemical signal was greatly enhanced compared with the undoped graphene modified GCE. Under the optimized conditions, the present sensor showed excellent performances for nimodipine detection including wide linear range of 0.02–3 μM, low detection limit (9.1 nM), good selectivity to the general coexisted interferences, etc. The proposed biosensor was also successfully applied to validate its capability for the analysis of nimodipine in tablets. The work would promote the potential application of NGE as an excellent material in fabricating electrochemical sensors for chemical or biochemical analysis. [ABSTRACT FROM AUTHOR]

Poly(3-methylthiophene)/nitrogen doped graphene modified glassy carbon electrode (P3MT/NGE/GCE) was prepared through simple drop-casting of NGE, followed by the electrodeposition of P3MT film for sensitive electrochemical determination of trace amounts of pesticide phoxim. The morphology and structure of P3MT/NGE/GCE were characterized by scanning electron microscopy; the electrochemical behavior of P3MT/NGE/GCE was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and chronocoulometry. The preparation conditions of modified electrode, the dropping amount of NGE and polymerization laps of P3MT, were optimized. Under the optimized conditions, the reduction peak current of cyclic voltammetric curve varied linearly with the concentration of phoxim over the two linear ranges of 0.02–0.2 μM and 0.2–2.0 μM, and the low detection limit was 6.4 nM according to lower linear range (S/N = 3). The sensor also exhibited excellent selectivity to phoxim over a wide range of possible interferents including ions, biomolecules, common environment pollutants and widely-used organophosphate pesticides. Moreover, the satisfactory practical feasibility of the sensor was evaluated by the environmental phoxim measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] PEDOT/NGE modified electrode was fabricated via CV method using nitrogen-doped graphene (NGE) coated GCE. [•] Highly reversible and well-separated redox couples of hydroquinone (HQ) and catechol (CT) were obtained at PEDOT/NGE/GCE. [•] A facile electrochemical sensor based on PEDOT/NGE/GCE was developed for simultaneous detection of HQ and CT. [Copyright &y& Elsevier]

Highlights: [•] The stable blue fluorescent GQDs were obtained via a hydrothermal method using reoxidized GO. [•] The fluorescence of GQDs were effectively quenched by Cu(II). [•] A facile fluorescent sensor based on GQDs has been developed for the detection of Cu2+ ions. [•] The sensor shows high sensitivity and selectivity to Cu2+ ions. [ABSTRACT FROM AUTHOR]