A simple low-temperature synthesis of fluorescent boron quantum dots for versatile applications

It is the first time to report the synthesis of small-molecule passivated boron quantum dots (BQDs) through a bottom-up strategy using L-cysteine (L-Cys) as a passivation agent and ammonium pentaborate tetrahydrate and boric acid as boron sources under a low reaction temperature of 100 °C. The morphology and surface structure of the prepared BQDs were characterized in detail using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The as-obtained BQDs emitted blue fluorescence with a quantum yield of 1.14%, and the particle sizes are mainly distributed between 1.5 nm and 3.5 nm. Stability research results demonstrated that BQDs possess high stability performance. The findings revealed that BQDs could be used as a fluorescence nanoprobe for developing a fluorescence “turn-off/turn-on” sensing platform to detect the drug molecule sulfasalazine (SSZ) and Pb2+. The proposed sensor indicates high sensitivity and selectivity towards SSZ, and the linear response range is 1–100 μmol L−1 with a detection limit of 0.9 μmol L−1. The quenched fluorescence could be recovered by Pb2+ in the range of 40–180 μmol L−1 with a detection limit of 39.7 μmol L−1. The proposed “turn off-turn on” sensor gives satisfactory results for practical sample analysis. Meanwhile, the thermodynamic data were estimated, and the corresponding quenching mechanisms were also discussed in detail. Moreover, BQDs had low cytotoxicity, which presented a potential application in cell imaging. They can also be used in the construction of LED and fluorescent film.