l-Histidine functionalized MXene quantum dots as novel fluorescent sensors for wide range detection of methyl orange

The wide-range and highly selective detection of toxic dye molecules remains an important challenge in environmental analysis. As an organic synthetic dye, methyl orange (MO) can pose considerable health risks even at low concentrations. Although diverse analytical approaches have been established for the detection of MO, the simultaneous achievement of a broad detection range and high selectivity remains challenging. Herein, nitrogen-functionalized MXene quantum dots (N-MQDs) were fabricated and employed for the first time as fluorescent probes for MO detection. N-MQDs were obtained using 2D MXene Ti₃C₂ nanosheets and l-histidine as raw chemicals via the hydrothermal method. Notably, l-histidine, a non-toxic dopant, was utilized for the first time in the preparation of N-MQDs. Furthermore, the introduction of l-histidine contributed to the passivation of surface defect sites in N-MQDs, resulting in bright fluorescence emission. N-MQDs exhibited a detection limit of 0.02 μM for MO and a detection range of 0.05-450 μM, which is wider than those of most reported methods for MO detection. N-MQDs were applied to the detection of MO in real water samples, and satisfactory spike recovery values were obtained. Mechanistic investigation of the response toward MO demonstrated that the fluorescence quenching of the N-MQDs by MO was attributed to Förster resonance energy transfer. The results obtained in this work demonstrate that N-MQDs are promising fluorescence probes for MO detection and show great promise in environmental monitoring applications.