Dual-channel sensing strategy for melatonin detection based on iron-cobalt oxide nanosheets with peroxidase-like activity and gold nanoclusters

This work developed a sensitive fluorescence and colorimetric dual-channel sensing system for melatonin determination based on iron-cobalt oxide nanosheets (FeCo-ONSs) and gold nanoclusters (AuNCs). FeCo-ONSs exhibited excellent peroxidase (POD)-like activities, that could catalyze H2O2 to produce reactive oxygen species and further catalyze N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium (TOPS) to couple with 4-amino-antipyrine (4-AAP) to generate purple compounds (PCs), which had absorption at 549 nm. The generated PCs can quench the fluorescence of AuNCs at 577 nm via fluorescence resonance energy transfer (FRET). The process of the generation of purple compounds would be restrained in existence of melatonin due to its scavenging capacity for free radicals. As a consequence, the absorption at 549 nm decreased, while the fluorescence quenching of AuNCs was weakened, and emission intensity at 577 nm progressively recovered. The recovery of fluorescence and the decrease in absorption depended on the concentration of melatonin. Therefore, by employing fluorescence and colorimetric dual signal monitoring, the linear ranges of melatonin were 5-300 mu M and 5-800 mu M, and the LODs were 1.17 mu M and 2.13 mu M, respectively.