A colorimetric biosensor using Fe3O4 nanoparticles for highly sensitive and selective detection of tetracyclines

A novel colorimetric biosensor for the determination of tetracyclines (TCs) based on the Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) is presented in this paper. TCs are known to have a strong tendency to complex with metal ions such as Fe(II) and Fe(III) on the surface of Fe3O4 MNPs. Experiments results show that the complexation of Fe3O4 MNPs and TCs could lead to the accelerated catalysing H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by Fenton chemistry. The reaction starts with oxidation of Fe3O4 MNPs-TCs complex by dissolved oxygen to generate reactive oxygen species (ROS), primarily ·OH, leading to deepen the color of the solution. Analysis results can be seen with the naked eye and monitored by UV–vis spectra. Under the optimal conditions, the detection limits are 26 nM for oxytetracycline (OTC), 45 nM for tetracycline (TC) and 48 nM for doxycycline (DOX). Moreover, this method has been applied for the determination of OTC content in drugs with satisfactory results. The proposed colorimetric biosensor is advantageous over other conventional methods in terms of convenient operation without any complicated chemical synthesis, modification, or tedious experimental procedures and its simple signal generation and detection by the naked eye. To the best of our knowledge, this is the first report on the enhancement effect of TCs on Fe3O4 MNPs-TMB-H2O2 reaction and its application in colorimetric TCs analysis. The designed colorimetric strategy may provide a promising alternative detection for TCs in clinical samples.