Upconversion fluorescence of MXene nanosheets and the sensitive detection of L-tryptophan

Abstract

Innovating the fluorescence characteristic of MXene nanosheets and quantum dots could result in fascinating perspectives in the applications of sensing, imaging and photocatalysis. However, the currently reported MXene-based materials have only shown down-conversion fluorescence emission, while the exploration and research of up-conversion fluorescent performance are scarce. Herein, the upconversion emission behaviors of Ti3C2 MXene nanosheets are reported and investigated for the first time. It was observed that the Ti3C2 nanosheets present upconversion emission in a wide wavelength range with adjustable color, covering almost the entire visible spectrum. The unique features of larger anti-stokes displacement (over 200 nm), narrower full width at half maximum (~17 nm) and longer lifetime (1.18 µs) were also exhibited, which are superior to those of the down-conversion fluorescence. The self-quenched fluorescence of the Ti3C2 nanosheets on the side of the highest fluorescence emission was also displayed. Based on the quenching effect of L-tryptophan on the Ti3C2 fluorescence by a fast charge transfer mechanism, a fast, simple and label-free fluorescence sensor for L-tryptophan detection was realized with a detection limit as low as 91 nM, which provides a valuable tool to widen their applications in food safety and diagnostics.