Portable smartphone enabled colorimetric detection of tetracycline in commercial milk samples via peroxidase-mimicking ZnO–Pd nanobolts

Abstract

Tetracyclines (TETs) are widely used broad spectrum antibiotics with low molecular weight. However, excessive use of these bacteriostatic agents has led to their residual increase in the food chain. The presence of TET residues adversely affects human health and the environment. For the detection of trace amounts of antibiotics, the development of ultrasensitive methods is essential. Herein, we have studied the activity of ZnO–Pd nanobolts for the detection of TET. The detection assay was based on the peroxidase mimetic ability of the nanozyme to oxidise a chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. By the activity of nanozyme the colorless TMB got oxidised into blue color ox-TMB. A turn-off approach was adopted for the detection of TET. In this process, oxidation of TMB was restricted in the presence of TET. The increasing concentrations of TET led to the disappearance of the blue color. The reactions were carried out under optimized conditions. The sensitivity of the assay was evaluated over a range of 0.001–102.4 µM. The specificity of the developed detection assay was analysed by testing various serum interfering analytes along with TET. All the reaction assays were evaluated using the absorbance values obtained by UV-Vis spectroscopy. The LOD and LOQ of the assays were reported to be 0.0029 µM and 0.0087 µM respectively. The relationship between the intensity and the increasing concentrations of TET was also studied using a smartphone, by evaluating the RGB values of the captured images.