Ratiometric fluorescent and smartphone-assisted dual-mode sensor for folic acid determination based on N-Nb₂C...

Accurate detection of folic acid (FA) content in foods is crucial for guiding dietary supplementation and mitigating risks associated with deficiency or overdose. However, most current methods have limitations in on-site visual detection. This study addresses this gap by developing a dual-mode ratiometric fluorescent and smartphone-assisted sensor (N-Nb₂C QD/CQDs). The internal filter effect between the sensor and FA significantly changed the fluorescence intensity ratio and produced continuous fluorescence color changes. The fluorescence color was converted to RGB values using smartphone, enabling visual and quantitative determination of FA. Under optimal parameters, the linear ranges for detecting FA were found to be 0.1-400 and 0.1-350 μM for fluorescence spectrometer and smartphone-assisted sensor. The detection limits were 87 and 189 nM, respectively. Furthermore, the sensor was successfully applied to direct visual identification of FA in samples of orange juice, oatmeal and urine, indicating the possibility of its practical application.