Ultrasensitive point-of-care testing of arsenic based on a catalytic reaction of unmodified gold nanoparticles

Nowadays, there is an urgent demand to develop methods for rapid and onsite determination of toxic arsenic in environmental samples. Herein, we propose a colorimetric method for ultrasensitive point-of-care testing of arsenic using unmodified gold nanoparticles (Au NPs). This system is based on the Au NP catalyzed redox reaction between Rhodamine B (RhB) and sodium borohydride (NaBH 4 ), which leads to a color change of the reaction solution. AsO 2 − significantly inhibits the catalytic activity of Au NPs so that it can be quantified by colorimetric measurements. The method shows high sensitivity with a detection limit of 0.64 ppb, which is below the threshold of arsenic in drinking water recommended by the WHO. It also demonstrates high selectivity among other interfering ions. Samples from daily life are analyzed using this method, and the results agree with those obtained from standard inductively coupled plasma mass spectrometry.