A multistep paper-based analytical device (mPAD) was designed and applied to the voltammetric determination of total inorganic arsenic. The electrodeposition of gold nanoparticles on a boron-doped diamond (AuNP/BDD) electrode and the determination of total inorganic arsenic is accomplished with a single device. Total inorganic arsenic can be determined by first reducing As(V) to As(III) using thiosulfate in 1.0 mol L-1 HCl. As(III) is then deposited on the electrode surface, and total inorganic arsenic is quantified as As(III) by square-wave anodic stripping voltammetry the potential range between -0.25 V and 0.35 V (vs. Ag/AgCl), best at around 0.05 V. Under optimal conditions, the voltammetric response for As(III) detection is linear in the range from 0.1 to 1.5 μg mL-1 and the limit of detection (3SD/slope) is 20 ng mL-1. The relative standard deviation at 0.3, 0.7 and 1.0 μg mL-1 of As(III) are 3.6, 4.3 and 3.3, respectively (10 different electrodes). The results show that the assay has high precision, a rather low working potential, and excellent sensor-to-sensor reproducibility. The method was employed to the determination of total inorganic arsenic in rice samples. Results agreed well with those obtained by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Graphical abstract A multistep paper-based analytical device (mPAD) is described that integrates a AuNP/BDD electrode preparation step and a detection step into a single device. The AuNPs are easily deposited on the BDD electrode by applying electrodeposition potential. The total inorganic arsenic concentration in rice samples was determined by using square-wave anodic stripping voltammetry.
Keywords: Arsenic detection; Electrochemical detection; Metal nanoparticles; Portable sensor; Rice sample; Thiosulfate.