A Magnetite–Cerium Oxide Nanocomposite‐Based Electrochemical DNA Biosensor for Highly Sensitive Detection of 4‐Nonylphenol in Food Samples

In this work, a novel electrochemical DNA biosensor was developed for the quantitative detection of 4‐nonylphenol (NPh) based on its ability to damage DNA. The surface of a carbon‐based screen‐printed electrode (SPE) was modified with magnetite (Fe 3 O 4 ) and cerium (IV) oxide (CeO 2 ) nanoparticles (NPs) to form a nanocomposite platform for enhanced electron transfer. Fish‐sperm DNA (fsDNA) was immobilized on the CeO 2 –Fe 3 O 4 NPs/SPE surface to construct the fsDNA/CeO 2 –Fe 3 O 4 NPs/SPE biosensor. The analytical response was evaluated using guanine (Gu) and adenine (Ad) oxidation signals, which decreased in proportion to NPh‐induced DNA damage. The biosensor exhibited linear response ranges for NPh of 0.022–3.0 nM based on Gu and 0.017–3.0 nM based on Ad signals, with detection limits of 0.007 and 0.005 nM, respectively. The binding constant ( K b ) of the fsDNA–NPh complex was calculated as approximately 10 8 M −1 , indicating a strong interaction. The biosensor's applicability was demonstrated in food samples, yielding recoveries of 97.85% and 101.37%.