Dual-Mode Fluorescence/UV-Vis Sensing Platform Based on Luminescence Modulation of Upconversion Nanoparticles

Upconverting nanoparticles (UCNPs) composed of sodium yttrium fluoride (NaYF₄) nanocrystals doped with trivalent rare-earth ions are synthesized by a co-precipitation method. Under 980 nm excitation, the UCNPs exhibit two prominent emission bands, both of which undergo significant quenching upon introduction of lycopene. Laser-induced fluorescence measurements reveal a pronounced decrease in luminescence intensity following lycopene addition. UV-visible absorption and steady-state fluorescence spectroscopy further demonstrate a linear correlation between lycopene concentration and signal attenuation. The limit of detection (LOD) for the UV-Vis assay is 328 ppm, while fluorescence detection attains an LOD of 234.5 ppm. Correlation coefficients (R²) of 0.9931 (UV-Vis) and 0.9958 (fluorescence) and relative standard deviations (RSD) of 3.9% and 1.76%, respectively, indicate high analytical performance. Quenching behavior is rationalized in terms of energy transfer mechanisms, underscoring the potential of UCNP-lycopene systems for optical sensing applications.