Design of smartphone platform by ratiometric fluorescent for visual detection of silver ions

In this work, a smartphone platform based on ratiometric fluorescence signals was reported, which can achieve fast, sensitive, and on-site visual detection of silver ions. The ratiometric fluorescent probe was constructed with fluorescein isothiocyanate (FITC) and telluride quantum dots (CdTe QDs) through electrostatic interaction. Silver ions will interact with -SH on the surface of CdTe QDs, which can cause the decrease of the fluorescence intensity at 680 nm, while the fluorescence of FITC at 522 nm remains unchanged. It displays the obvious color changes from orange-red to light yellow to green. Based on the changes, the portable smartphone platform was used to identify the RGB values of the system. Then, an analysis model was established according to the variation of RGB values for the visual analysis of Ag+. Under the best experimental conditions, the detection limit of Ag+ by fluorescence spectrometer analysis can be as low as 3.65 nM, the linear range was 12.50 nM to 500 nM. Additionally, the linear range of smartphone platform was 0.125–12.5 μM, and the detection limit was 40 nM. Therefore, visual on-site analysis of Ag+ in environmental water samples can be achieved by capturing the obvious color changes of the system on a smartphone platform.