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

A cost-effective, facile, and sensitive fluorescence sensing strategy for Pb 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 Pb ions from the solution via Pb-GSH complexes. Pb 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 TiO 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 Pb ions with a detection limit as low as 4.1 × 10 mg mL. More importantly, the long observation length combined with a small volume enabled a sample acquisition volume of only 2.1 × 10 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.