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.