A smartphone-based fluorescent sensing system for simultaneous visual detection of chromium(Ⅲ) and copper(Ⅱ) ions

In this work, we developed a highly accurate and sensitive two-emission fluorescence sensor, integrated with a smartphone, for the rapid detection of Cu²⁺ and Cr³⁺ in aqueous solution. This sensor comprised AgInS/ZnS quantum dots (AIS/ZnS QDs) and metal-AIEgen frameworks (MAFs). Upon mixing in a specific ratio, the hybrid system can emit a white light when exposed to a UV lamp (365 nm). The system demonstrates distinct fluorescence variations upon interaction with Cr³⁺ or Cu²⁺. Specifically, the sensor transitions from white to red or blue when exposed to Cr³⁺ or Cu²⁺, respectively. By utilizing smartphone color recognition software to measure the ratio of red to blue (R/B) value of the solution, the detection ranges of the dual response sensor for Cr³⁺ and Cu²⁺ are established at 250–5000 nM and 100–2500 nM, with detection limits of 168.4 nM and 101.1 nM, respectively. The practicality of the sensor is validated through quantitative measurement of RGB values from real water samples, including drinking water, tap water, and lake water. Consequently, this sensor exhibits significant potential for point-of-care detection, attributable to its low cost, portability, and high specificity and sensitivity.