MgO Nanocubes as Self-Calibrating Optical Probes for Efficient Ratiometric Detection of Picric Acid in the Solid State

Fluorescence intensity ratio (FIR)-based optical sensing where ratio between the intensity of two different wavelength emissions is considered for analyzing sensing performance have advantages over the conventional single wavelength emission based sensing in various aspects. Here, we have demonstrated the MgO nanocubes, synthesized by simply heating Mg ribbons in air atmosphere, for possible self-calibrated picric acid (PA)-sensing application by employing FIR-based technique in solid state. The as-prepared MgO nanocubes at 600 and 1200 °C show two emission peaks with both 355 and 532 nm excitation. The intensity ratio between these two emissions is considered for PA sensing. With an increase in the PA concentration, the PL intensity of both the peaks decreases: One with a faster rate as compared to that of the other one. Hence, the ratio is considered for sensing applications. The decrease in the PL intensity is possibly due to a static quenching process, following ground-state electron transfer from MgO to PA. Interestingly, the nanocubes show high stability and longevity for repeated washing cycles.