TiO2 Nano-test tubes as a solid visual platform for sensitive Pb2+ ion detection based on a fluorescence resonance energy transfer (FRET) process.

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.