The early nucleation stage of gold nanoparticles formation in solution as powerful tool for the colorimetric determination of reducing agents: The case of xylitol and total polyols in oral fluid

Herein we report a simple non-enzymatic assay for xylitol and total polyols in water and oral fluid based on the time resolved formation of gold NPs in solution, and their colorimetric detection at fixed wavelength (520 nm). The key novelty of the proposed approach relies on the exploitation of information given by the early nucleation step of NPs formation instead of those related to final products at the end point of AuNPs growth, as generally reported in literature. We demonstrate that the nucleation stage is linearly correlated to the concentration of the reducing agent in solution. On the contrary, the optical reading carried out the end point of the reaction shows non-linear correlation and several undesired features. As case study, we applied the proposed method to xylitol and polyols determination, first tested in water and spiked oral fluid samples. The detection limits obtained on xylitol resulted 180 mg L-1 (CV% = 6.9) and 44 mg L-1 (CV% = 6.5) in water and oral fluid, respectively. Afterward, we successfully performed the monitoring of total polyols in oral fluid over time during xylitol-containing gums consumption. Data here reported show high correspondence with available data in literature. The proposed approach is fast, cheap, highly reproducible, and can be extended to other reducing substances of interest for analytical purposes.