Ultrafine FeCuAgCeGd–based high–entropy nanozyme: Preparation, catalytic mechanism, and point–of–care detection of dopamine in human serum

Point–of–care testing (POCT) plays vital role in clinic field, especially in resource–limited areas. The nanozyme–based colorimetric platform is the potential strategy for POCT. Therefore, a high–entropy allay nanozyme (HEAzyme) was prepared via formaldehyde–assisted metal–ligand crosslinking method using multi–metal (FeCuAgCeGd) species. The obtained FeCuAgCeGd–HEAzyme showed coordination nanoparticles with ultrafine size (average size was approximately 5 nm). The peroxidase–like (POD–like) activity of FeCuAgCeGd–HEAzyme was verified through density functional theory (DFT) calculations, demonstrating the capability of FeCuAgCeGd–HEAzyme to catalyze H2O2 and generate hydroxyl radicals (•OH). These radicals can oxidize colorless 3,3′,5,5′–tetramethylbenzidine (TMB) to blue oxTMB. Dopamine (DA) scavenges •OH, resulting in an “on–off” effect for TMB oxidation. Subsequently, an FeCuAgCeGd–HEAzyme colorimetric sensor was developed for DA detection, which features a low detection limit of 0.77 µM and a linear range of 5.0–70.0 µM. The sensor demonstrated a recovery ratio in spiked serum samples ranging from 97.7 % to 104.3 % with high stability and favorable selectivity. Furthermore, an FeCuAgCeGd–HEAzyme POCT platform was designed for on–site detection of DA, achieving a reliable linear detection range (5.0–70.0 µM) and a low detection limit (5.69 µM). This platform offers a facile and efficient strategy for rapid, visual, and on–site DA detection in clinical settings with advantages of cost–effectiveness and ease of operation.