Highly sensitive and selective detection of selenate in water samples using an enzymatic gold nanodendrite biosensor

Gold (Au) and glassy carbon (GC) electrodes have been decorated with gold nanodendrites (NDs) using galvanic replacement reactions. Modification of the ND surfaces by lipoic acid N-hydroxysuccinimide ester allows to immobilise selenate reductase (SeR) to the electrode surface, rendering it selective for the catalytic reduction of selenate (SeO42-, Se(VI)) to selenite (SeO32-, Se(IV)). Electrode modifications have been characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). For selenate detection, CV and differential pulse voltammetry (DPV) measurements have been carried out in HEPES buffer with pH 6.0. Under optimum conditions, the linear range for Au electrodes decorated with AuNDs was 0.3-203 µg/L Se with a limit of detection of 0.01 µg/L Se, which is a 274-fold improvement over using non-nanostructured surfaces for selenate detection. Other anions such as SO42−, NO3-, NO2-, PO43-, AsO43- and SeO32- did not interfere with the detection of selenate. The electrochemical sensor was used for the detection of selenate in three different real samples with recovery between 98.5-102.0%.