Dual-readout assay for determination of Ag+ and Cu2+ based on in situ fluorogenic and chromogenic reaction between dopamine and naphthoresorcin

Silver ions (Ag+) and copper ions (Cu2+) are toxic environmental pollutants, and their excess accumulation can cause adverse effects on human health. Thus, the development of a simple, convenient, economic and sensitive sensor for Ag+ and Cu2+ is an urgent need. Herein, we find that the fluorogenic and chromogenic reaction between dopamine (DA) and naphthoresorcin (NR) could be effectively facilitated by Ag+ or Cu2+, with significant increase of fluorescent and colorimetric signals. Accordingly, we report a novel "turn-on" dual-mode sensor for directly fluorescent and colorimetric detection of Ag+ and Cu2+. Mechanistic investigation reveals that Ag+ serves as an oxidant while Cu2+ acts as a catalyst to facilitate DA and NR reaction. By incorporating EDTA and NaCl, Ag+ and Cu2+ could be selectively measured at concentrations as low as 157.1 nM and 11.9 nM, respectively. Applicability of this sensor to detect Ag+ and Cu2+ in real water samples has also been demonstrated through a mix-and-detect procedure, and the detection results obtained by dual-readout modes agree well with correspond to those from inductively coupled plasma–mass spectroscopy (ICP-MS). This dual-mode detection method provides the advantages of simplicity, easy-operation and low experimental cost without any sophisticated synthesis, modification or labeling process, which is promising for inspection of Ag+ and Cu2+ in environmental water samples.