Design and Applicationof Flower-like Iron Single-AtomNanozymes for Sensitive Colorimetric Detection of Caffeic Acid

Herein we present a strategic engineering approach to develop flower-like iron single-atom nanozymes (Fe/NC-F) with exceptional catalytic performance, which are hierarchically anchored on three-dimensional carbon flower substrates fabricated from nanosheet assemblies. This innovative platform enables the construction of a sensitive and straightforward colorimetric assay for caffeic acid (CA) detection. Fe/NC-F single-atom nanozymes engineered through a template-directed synthesis protocol combined with high-temperature pyrolysis exhibit bioinspired Fe–Nx-coordinated active sites analogous to those of natural enzymes and achieve exceptional single-atom dispersion. On the basis of the exceptional peroxidase-like activity inherent in Fe/NC-F, a colorimetric sensing platform for the quantitative determination of CA was developed. This system has a broad linear working range (0.04–20 μM) with a low detection limit of 12 nM. To achieve rapid onsite detection, a CA visualization sensing platform with a linear range of 0.5–20 μM and a detection limit of 143 nM was further constructed via a smartphone app. This method was not only successfully implemented to detect CA in actual samples of coffee and blueberries but also provided a reference strategy for the design of single-atom nanozymes with high catalytic activity.