Polyoxometalate-based composite: a dual-functional platform for cytochrome C separation and colorimetric sensing of ascorbic acid.

A novel Co9S8/PW₁₁ composite was synthesized via a facile hydrothermal method. The composite exhibited specific adsorption toward cytochrome C (Cyt-c) at pH 10, achieving an adsorption efficiency of 92.8%. The adsorption behavior followed the Langmuir isotherm model with a maximum adsorption capacity of 209.59 mg·g-1. The method was successfully applied to the selective isolation of Cyt-c from complex biological sample and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that the separated protein had high purity. In addition, the resulting Co9S8/PW11@Cyt-c system possessed peroxidase-like activity, capable of catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to a colored product. Ascorbic acid was found to effectively inhibit this oxidation and decolorize the system, enabling the development of a colorimetric assay for ascorbic acid determination in food samples. Under optimized conditions, the method exhibited a good linear response in the range of 0-100 μM, with a detection limit of 0.68 μM, and demonstrated practical applicability for quantitative analysis of real food specimens. Collectively, these results demonstrate that the Co9S8/PW11 composite serves as a versatile platform, showing outstanding performance in both the efficient purification of Cyt-c and the construction of sensitive sensing systems.