Dye‐Sensitized Core/Shell Upconversion Nanoparticles for Detecting Nitrites in Plant Cells.

A fluorescent nanoprobe is reported for rapid detection of nitrites (NO2−) in plant cells. The probe is fabricated by linking neutral reds (NR) to the surface of upconversion fluorescent core/shell nanocrystalline with the bridging of polyethylene glycol (PEG) molecules. The fluorescence of upconversion nanoparticles (UCNPs) is stored by NR through fluorescence resonance energy transfer (FRET) under 980 nm excitation that can be released by further linking to NO2−. It is observed that the intensity rate of green to red emission of NR‐modified UCNPs changes linearly with increasing the amount of NO2−. So that concentration of NO2− can be accordingly addressed. Worth mentioning is that, comparing with bare core upconversion nanoparticles (NPs), core/shell UCNPs can greatly reduce the surface quenching of the fluorescence induced by solvents instead of NR and thus leading to the enhancement of signal‐to‐noise ratios. Moreover, excitation of core/shell UCNPs requires only a much lower power (0.06 W cm−2) than bare cores which is beneficial to reducing the decomposition of NR to stabilize the FRET processes. Under the optimum conditions, the detection limit of nitrite in plant cells was 0.1 µg mL−1. [ABSTRACT FROM AUTHOR]