Polydatin-based natural product as an activatable molecular sensor toward viscosity detection in liquid

Effective and non-invasive inspection method toward viscosity is expected to ease the burden of continued increased health problems worldwide. Herein, we proposed that viscosity is one of the most important markers in the liquid microenvironment. Then, a natural product was further developed from resveratrol derivate, polydatin, as an activatable molecular sensor for monitoring liquid micro-environmental viscosity alterations for metamorphic extent determination. This natural molecular sensor was constructed by the single double bond alternating conjugate structure, which can rotate freely in the low viscosity media, and in the highly viscous media, bright fluorescent signals are specifically activated (around 383 nm, 53-fold), endowing the natural sensor with the capacity to avoid autofluorescence from the additives and achieving high signal-to-noise ratio imaging. With the lower detection limit 1.125 cP, the sensor polydatin exhibits higher viscosity sensitive coefficient (0.60), and 75.5 nm of Stokes shift was found in the distilled water. Afterward, polydatin achieved non-invasively identifying the thickening effects of food thickeners. In addition, the capability of polydatin to evaluate the deterioration extent of liquids with viscosity as a robust marker was explored. It was found that the viscosity level in microenvironments is highly dependent on the liquid food metamorphic period. The fluorescent intensity increment and viscosity value changes were fitted into a linear equation. We expected that this approach would reinvigorate the fluorescent analytical methods toward liquid safety inspection.