Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA

In this work, a ratiometric fluorescence sensing platform was established to detect Cu²⁺ and D-PA (d-penicillamine) based on nitrogen-doped Ti₃C₂ MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu²⁺ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu²⁺, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu²⁺ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu²⁺ (3.0 nM) and D-PA (0.115 μM), coupled with excellent sensitivity and stability.