Field-deployable ratiometric fluorescent hydrogel sensor based on MoS₂QDs/CdTe@SiO₂ for smartphone-enabled visual...

Conventional solution-based fluorescent probes are often constrained in practical application by insufficient portability and a reliance on complex instrumentation. To overcome these limitations, this study developed a portable, hydrogel-based ratiometric sensor integrated with a smartphone readout platform for the visual, on-site detection of Cu²⁺. The sensor was synthesized by co-embedding blue-emissive MoS₂ quantum dots (QDs) and red-emissive CdTe QDs@SiO₂ nanoparticles within a gelatin/glycerol hydrogel matrix. Upon exposure to Cu²⁺, the sensor exhibits a distinct colorimetric transition from blue to red, which is quantitatively captured and detected using a smartphone color analysis application. This method achieves a detection limit as low as 33.2 nM and demonstrates excellent long-term stability (32 days). The sensor's practicality was validated through the analysis of environmental water samples, yielding high accuracy and reproducibility. This work establishes a novel, portable, and instrument-free ratiometric hydrogel sensor strategy, leveraging smartphone technology for effective on-site Cu²⁺ monitoring in water resources.