Transformative Antioxidant Testing of Chinese Herbal Medicine Polysaccharides with Colorimetric Assays Using Fe/NC Nanozymes

The antioxidant capacity of Chinese herbal medicine polysaccharides (CHMPs) is crucial for evaluating their nutritional and medicinal value. Therefore, the assessment of the total antioxidant capacity (TAC) in CHMPs is of significant importance. Existing TAC detecting methods suffer from limited sensitivity and intricate processes. Here, we exploited nitrogen-doped carbon decorated with Fe (Fe/NC) as a peroxidase-like nanozyme to assess the TAC in CHMPs. Fe/NC nanozymes exhibit an enhanced affinity for hydrogen peroxide (H2O2), catalyzing the generation of hydroxyl radicals (•OH) that oxidize the colorless TMB substrate into the blue-colored oxTMB with the characteristic absorbance at 652 nm. With the introduction of CHMPs, the oxidation of the colorimetric substrate was alleviated due to the free radical scavenging abilities of CHMPs. The sensor demonstrates a broad linear detection range (3.91–125 μg mL–1 for lycium barbarum polysaccharide (LBP), 7.81–125 μg mL–1 for salvia miltiorrhiza polysaccharide (SMP), and 15.62–125 μg mL–1 for panax notoginseng polysaccharide (PNP)) with low limits of detection (LODs: 0.38 μg mL–1 for LBP, 5.44 μg mL–1 for SMP, and 5.14 μg mL–1 for PNP). Based on this, we successfully detected TAC in three CHMPs. Furthermore, this sensor has been effectively utilized in the assessment of TAC in extracts from Chinese herbal medicines. Our findings highlight the potential of Fe/NC nanozymes as a versatile and sensitive tool for the analysis of CHMPs, offering a perspective on the application of nanozyme-based sensors in herbal medicine research.