Highly Selective Photoelectrochemical Assay of Arsenate Based on Magnetic CoO-FeO Cubes and the Negative-Background Signal Strategy.

Water pollution presents a significant environmental concern on earth. Herein, due to the serious environmental harmfulness of arsenate [As(V)], an iron phthalocyanine (FePc)-induced switchable photocurrent-polarity platform was developed for highly selective assay of As(V). First, magnetic CoO-FeO cubes were obtained by calcination of the CoFe Prussian blue analogue and then functionalized with oligonucleotide (S1). In the presence of As(V), S1 could be released based on the stronger affinity between As(V) and CoO-FeO cubes. After magnetic separation by CoO-FeO cubes, the released S1 was used to trigger the catalytic hairpin assembly (CHA) and hybridization chain reaction, resulting in the formation of lots of G-quadruplex structures on the AgInS/ITO electrode. Then, the capture of FePc by the G-quadruplex led to the switch of the photocurrent polarity of the AgInS/ITO electrode from the anode to the cathode. Thus, As(V) was sensitively assayed with a low detection limit of 1.0 nM and a wide linear response range from 10 nM to 200 μM. This meets the detection requirement of the World Health Organization for the arsenic concentration in drinking water [less than 10 μg L (130 nM)]. In addition, whether it was cationic or anionic interferents except phosphate (PO), only As(V) could generate the cathodic photocurrent, effectively avoiding the false-positive or false-negative results during As(V) assay. Interestingly, As(V) was also simultaneously separated from the detection system by CoO-FeO magnetic cubes. The proposed photoelectrochemical platform may have a great potential application for the selective detection of As(V) in environmental fields.