Copper-cerium layer double hydroxide as a novel tool for melatonin detection in sleep therapy tablets

Sleep disorders are among the most common health concerns leading to health disorders. To address this problem, a copper-cerium layered double hydroxide (Cu-Ce LDH) was developed as an efficient sensing material for the electrochemical detection of melatonin in sleeping pills. The Cu-Ce LDH enhanced oxidation by adsorbing melatonin through π-π and electrostatic interactions, facilitating electron transfer and improving conductivity from Ce³⁺ sites. The mixed valency states of Cu and Ce facilitated improved conductivity and high surface area. The enhanced electrochemical behaviour of Cu-Ce LDH increased redox activity to facilitate rapid electron transfer and efficient electrocatalytic performance. The amide and indole ring of melatonin created hydrogen bonds with water molecules and hydroxyl groups on the electrode surface. At pH 6, water molecules engaged in a nucleophilic interaction, leading to proton release and the formation of a 4,5-dihydroxyindole derivative. This compound transformed into a quinone through a reversible process or form a 2,7-dimer via an oxygen bridge. Owing to these properties, the proposed sensor exhibited excellent electrocatalytic behaviour, demonstrating a wide linear detection range (30 nM to 1200 µM), with a limit of detection and limit of quantification of 6.8 nM and 22.6 nM, respectively, in real sample Nizleep Pills compared with other sleep therapy tablets. The sensor demonstrated high selectivity (RSD = 2.83%). Moreover, it retained 74% of its initial response after 100 continuous cycles, indicating good stability. The Cu-Ce LDH electrocatalyst demonstrated excellent electron transfer, good stability and reproducibility. Furthermore, the reproducibility (RSD = 1.28%) for six modified electrodes highlighted its potential as a sensitive and reliable tool for pharmaceutical applications.