Fluorescent and smartphone-assisted colorimetric dual-mode sensor for Ag+ detection based on orange-red emitting carbon dots

A novel fluorescent and smartphone-assisted colorimetric dual-mode sensor is constructed for Ag+ monitoring based on orange-red emitting carbon dots (or-CDs). The as-synthesized or-CDs possess strict excitation independence and show specific response to Ag+. Ag+ can induce fluorescence quenching of the or-CDs through dynamic quenching characteristic. The quenching efficiency and Ag+ concentration show good linear relationships in the ranges of 0.8–10 μM and 10–100 μM with the limit of detection (LOD) down to 56 nM. More interestingly, these phenomena are accompanied by visible color conversion (red-brown) under the sunlight. So, we develop a portable smartphone-assisted colorimetry for Ag+ monitoring via the red-green-blue (RGB) analysis with the linear range of 10–80 μM and LOD of 0.78 μM. Furthermore, the or-CDs have realized the monitor of Ag+ in human serum and the Fenhe River with good recoveries (96.37–103.20%) and relative standard deviations (RSDs, <3%) by fluorescence and smartphone-based RGB analysis.