In this study, we developed a microfluidic paper analysis device (μPAD) for distance-based detection of Ag + in water. The μPAD was manufactured by wax printing method on filter paper. Then, a layer of gold nanoparticles (AuNPs) was deposited and ascorbic acid was printed on the channel. In the detection, Ag + was reduced by ascorbic acid and coated on the surface of the AuNPs on the channel, forming Au@Ag core/shell nanoparticles. Based on the capillary flow principle, different concentrations of Ag + formed different distances of color ribbons. Thus, quantitative detection of Ag + can be achieved by measuring the distance of the color ribbon. The detection limit of this method was as low as 1 mg•L −1 within 15 min and the interference of common metal ions in water can be eliminated. In conclusion, this method had successfully realized the leap from colorimetry to direct reading, realizing fast read and easy manipulation with low-cost.

In this study, a naphthalene Schiff-base P which serves as a dual-analyte probe for the quantitative detection of Al3+ and Mg2+ has been designed.

A novel ratiometric Cu2+-selective probe was rationally constructed based on pyrene derivative. Compared to other tested metal ions, the probe presented the selective recognition for Cu2+ which could be detected by a significant turn-on fluorescent response at 393 nm and 415 nm. Under the optimized conditions, a detection limit of 0.16 μM Cu2+ in aqueous media was found. Besides this, a 1:1 metal–ligand complex was confirmed by MS spectra and Job’s plot experiment, and the binding mode was also studied by 1H NMR experiment. Meanwhile, the fluorescence imaging in living cells was performed to detect Cu2+ with satisfactory results.