TiO₂ Nano-test tubes as a solid visual platform for sensitive Pb²⁺ ion detection based on a fluorescence resonance...

A cost-effective, facile, and sensitive fluorescence sensing strategy for Pb²⁺ ion detection has been developed based on the fluorescence resonance energy transfer (FRET) between carbon quantum dots (CQDs) and Au nanoparticles (NPs). Glutathione (GSH)-synthesized CQDs acted as both the fluorescence donor and the sorbent to extract Pb²⁺ ions from the solution via Pb-GSH complexes. Pb²⁺ ions on CQDs reacted with -SH groups on AuNPs to generate sandwich-type Au-PdS-CQDs, leading to a dramatic decrease in the fluorescence of the CQDs. To expand the potential applications of this strategy, we constructed a sensing strategy using self-organized TiO₂ nanotube arrays (TiNTs). The high aspect ratio and transparency for light emitted from the CQDs enabled the TiNTs to serve as a sensitive solid visual platform for the highly selective detection of Pb²⁺ ions with a detection limit as low as 4.1 × 10^-8 mg mL^-1. More importantly, the long observation length combined with a small volume enabled a sample acquisition volume of only 2.1 × 10^-3 μL, which is smaller than the traditional fluorescence analysis in solution and on commercially available test paper, thus endowing this visual platform with the potential for use in single-cell diagnostics.