Comparative Colorimetric Sensor Based on Bi-Phase γ-/α-Fe₂O₃ and γ-/α-Fe₂O₃/ZnO Nanoparticles for Lactate Detection

This work reports on Fe₂O₃ and ZnO materials for lactate quantification. In the synthesis, the bi-phase γ-/α-Fe₂O₃ and γ-/α-Fe₂O₃/ZnO nanoparticles (NPs) were obtained for their application in a lactate colorimetric sensor. The crystalline phases of the NPs were analyzed by XRD and XPS techniques. S/TEM images showed spheres with an 18 nm average and a needle length from 125 to 330 nm and 18 nm in diameter. The γ-/α-Fe₂O₃ and γ-/α-Fe₂O₃/ZnO were used to evaluate the catalytic activity of peroxidase with the substrate 3,3,5,5-tetramethylbenzidine (TMB), obtaining a linear range of 50 to 1000 μM for both NPs, and a 4.3 μM and 9.4 μM limit of detection (LOD), respectively. Moreover, γ-/α-Fe₂O₃ and γ-/α-Fe₂O₃/ZnO/lactate oxidase with TMB assays in the presence of lactate showed a linear range of 50 to 1000 µM, and both NPs proved to be highly selective in the presence of interferents. Finally, a sample of human serum was also tested, and the results were compared with a commercial lactometer. The use of ZnO with Fe₂O₃ achieved a greater response toward lactate oxidation reaction, and has implementation in a lactate colorimetric sensor using materials that are economically accessible and easy to synthesize.