Facile synthesis of hemin@PMo12 nanocomposite with peroxidase-mimicking activity for colorimetric detection of ascorbic acid in fresh fruits

Facile synthesis of Hemin@PMo 12 via manual grinding, no complex equipment and harsh conditions required. • Solid-phase Hemin@PMo 12 enables easy recovery, good reusability and high stability. • Hemin@PMo 12 shows excellent peroxidase-mimicking activity, outperforming natural HRP in kinetic parameters. • The sensor achieves accurate AA detection in apple samples via UV–vis and smartphone analysis. Polyoxometalate-based nanocomposites, as promising peroxidase mimetics for biosensing, have drawn extensive attention. In this study, a facile manual grinding method was developed for the synthesis of Hemin@PMo 12 nanocomposites from hemin and phosphomolybdic acid (H 3 PMo 12 ), without complicated equipment or harsh reaction conditions. Hemin@PMo 12 exhibited excellent peroxidase-mimicking activity, capable of catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ) to form a blue oxidized product. Ascorbic acid (AA) could specifically reduce the oxidized TMB, leading to a noticeable color fading and a significant decrease in absorbance, which enabled the colorimetric detection of AA. The proposed method based on Hemin@PMo 12 demonstrated a wide linear range of 3–200 μM and a low limit of detection (LOD) of 1.1 μM for AA detection. Furthermore, the developed sensor was successfully applied to the quantitative determination of AA in fresh fruit samples (e.g., apple), yielding satisfactory recoveries ranging from 98.4% to 102.7%. Notably, the solid-phase nature of Hemin@PMo 12 endowed it with prominent advantages of easy recovery from the reaction system and good reusability. These advantages well made up for the inherent drawbacks of traditional nanozymes, namely the difficulty in separation and the restriction to single-use applications. With the merits of simple synthesis, easy recovery, reusability, high sensitivity, and good selectivity, Hemin@PMo 12 provided a promising candidate for the development of practical, low-cost colorimetric sensors for AA detection in food analysis and related fields. The schematic representation of the synthesis of Hemin@PMo 12 and the dual-mode detection of ascorbic acid. Download: Download high-res image (95KB) Download: Download full-size image