Optical Determination of Tryptophan Using Persistent Luminescence Nanoparticles (PLNPs)

Tryptophan is an essential amino acid that is an important part of the human diet. In this work, label-free photoluminescence sensing based upon persistent luminescent nanoparticles (PLNPs) Zn0.8Ga2O4: Cr3+ is reported to determine tryptophan. Following 254 nm excitation, the PLNPs released luminescence after storing the absorbed light. Compared to the standard fluorescence, the persistent afterglow of the PLNPs was used for detection and imaging without external illumination, thereby eliminating autofluorescence and scattered light generated by biological substrates. For tryptophan concentrations from 4 to 240 µM, a linear relationship was described by F/F0 = 0.9416 − 0.0024 [Trp] with a correlation coefficient of 0.9911 and a detection limit of 0.19 µM. The recoveries of analyzed samples were between 97.9 and 101.9% providing good accuracy and simple methodology.