Label-free immunosensor based on graphene/polyaniline nanocomposite for neutrophil gelatinase-associated lipocalin detection

•A label-free immunosensor based on electropolymerized aniline on graphene/polyaniline nanodroplet has been developed.•The proposed system provides high sensitivity, high specificity and fast response toward NGAL detection.•This system was successfully applied to determine NGAL in urine sample.

A novel label-free electrochemical immunosensor for neutrophil gelatinase-associated lipocalin (NGAL) detection has been developed. The immunosensor has been constructed by immobilization of NGAL capture antibodies to electropolymerized aniline deposited on top of an electrosprayed graphene/polyaniline (G/PANI) modified screen printed carbon electrode. Electrospraying of G/PANI increases the electrode surface area while electropolymerization of aniline increases the number of amino groups (-NH2) for antibody immobilization. The factors affecting the sensor sensitivity (i.e. aniline concentration, scan number and scan rate of electropolymerization) have been optimized. In a prior report, Kannan et al. reported a broad oxidation peak in cyclic voltammetry upon the binding between NGAL with its antibody. In this study, a dramatic increase (58-fold) in the oxidation current upon the binding between NGAL and its antibody is obtained when compared to an unmodified electrode, verifying a substantial improvement in the electrochemical sensitivity of this system. Under optimal conditions, this system exhibits high sensitivity with a limit of detection (LOD) of 21.1 ng mL−1, wide linearity (50–500 ng mL−1) and high specificity toward NGAL detection from small samples (10 μL). As an example application, the sensor is tested for the detection of NGAL in human urine, and the results correspond well with the values obtained from a standard ELISA. Compared to the ELISA method, our system requires less analysis time (≤30 min/sample), less sample and less operating cost.

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