Photo-responsive Ce-hemin nanozyme-based portable colorimetric sensor for tetracyclines assay

A cerium ion-modified hemin polymer (Ce-hemin) was synthesized via a facile route, exhibiting photo-responsive oxidase-like activity and excellent stability. The Ce doping effectively prevented hemin aggregation, facilitated electron transfer, enhanced photocatalytic activity, and created a high adsorption capacity for tetracyclines (TCs). Taking advantage of the photo-sensitivity of TCs, a "turn-on" colorimetric sensing platform based on Ce-hemin nanozymes and smartphone-readout was constructed for visual analysis of TCs. This sensor offers a wide detection range and a low limit of detection (0.11 μM). The mechanism of the "turn-on" colorimetric performance was systematically discussed, which involves the abundant generation of superoxide radical anion (·O₂^-) species through photoexcitation of the surface complex between TCs and Ce-hemin. Furthermore, machine learning was employed for the accurate classification and identification of two representative TCs and chloramphenicol. Thus, this work provides an environmentally friendly strategy for the detection of TCs without H₂O₂, and also broadens the application of photo-responsive nanozymes in colorimetric sensors.