A ratio fluorescence/colorimetry/smartphone triple-mode sensor based on solvent-dominated signal amplification strategy for precise and rapid detection of melatonin in fruit juice.

A ratio fluorescence/colorimetry/smartphone triple-mode sensor based on Ru-CN was established for precise and rapid detection of melatonin (MT). Specifically, Ru-CN with fine luminous characteristic and peroxidase-like activity catalyzes the oxidation of OPD to generate luminescent DAP which in turn suppresses intrinsic fluorescence of Ru-CN because of the fluorescence inner filter effect (IFE). MT can inhibit this catalytic process, leading to partial recovery of the fluorescence of Ru-CN and the decrease in UV-vis signal of the reaction system, as well as the gradual fading of the yellow color of the reaction solution. Hence, this triple-mode sensor can realize precise, reliable, and high-throughput determination of MT with correlative detection limits of 0.32, 0.46, and 0.67 μM. Moreover, this triple-mode sensor has been applied to MT detection in multiple juice samples with recoveries ranging from 86.00 to 99.68%, which indicates the suitability of the novel idea for the research and development of multimode optical sensors for food analysis.