Nitro-functionalized nano-UiO-66/CdTe-QDs ratiometric probe for Sn2+ detection via redox-triggered fluorescence response.

In this work, a visual and equipment-free detection method for Sn²⁺ was developed based on the dual-emission nano-probe UiO-66-NO₂/CdTe-QDs. The probe was synthesized by physically mixing nano-CdTe QDs with nitro-functionalized UiO-66 nanoparticles, exhibiting dual fluorescence peaks at 428 nm (weak) and 650 nm (strong). Upon addition of Sn²⁺, redox reaction between the probe and Sn²⁺ occurs, producing a marked fluorescence enhancement at 428 nm and quenching at 650 nm, thereby generating a reversed ratiometric response. Nano-UiO-66-NO₂/CdTe-QDs demonstrates exceptional selectivity toward Sn²⁺, with a limit of detection of 32 nM and a linear range of 0-90 μM. More importantly, a naked-eye-discernible fluorescence color transition from pink to blue could be observed for nano-UiO-66-NO₂/CdTe-QDs along with the fluorescence titration process. Leveraging this change, portable sensors were fabricated by immobilizing nano-UiO-66-NO₂/CdTe-QDs onto the surface of filter paper. Based on the portable sensors, a smartphone-assisted, equipment-free detection platform for Sn²⁺ has been developed and applied for monitoring Sn²⁺ in real samples. Mechanistic studies confirm that fluorescence modulation originates primarily from the redox reaction between nitro groups and Sn²⁺.