Fluorometric detection and analog discrimination of melatonin by amide naphthotube-based indicator displacement assays.

Melatonin, a hormone synthesized by the pineal gland, is renowned for its pivotal role in governing circadian rhythms and its promising therapeutic attributes encompassing anti-inflammatory, anti-aging, and cancer-preventative properties. Nevertheless, the improper utilization of melatonin may lead to health hazards, highlighting the critical necessity for accurate detection of melatonin in pharmaceutical or biological samples. Furthermore, melatonin metabolites exhibit analogous chemical structures yet divergent pathophysiological functions, emphasizing the significance of distinguishing between these analogs. In this study, we report a supramolecular sensor that combines amide naphthotube and toluidine blue O in an indicator displacement assay for the quantitative detection of melatonin and differentiation of its analogs. The sensor demonstrated remarkable sensitivity, with a low detection limit of approximately 0.70 μM, and a broad dynamic range of 0.70-98.8 μM, along with excellent selectivity and stability. Notably, the sensor enables the determination of melatonin levels in various sample matrices, including milk, artificial urine, and pharmaceutical preparations. Through optimization of the host-guest complex ratio, our newly designed sensor effectively distinguishes melatonin from its six analogs. This approach addresses a current research gap, as existing macrocycles have limited capability to differentiate between melatonin analogs, with only a few achieving precise melatonin quantification.