Natural Enzyme-Inspired Design of the Single-Atom Cu Nanozyme as Dual-Enzyme Mimics for Distinguishing Total Antioxidant Capacity and the Ascorbic Acid Level.

Although various oxidase mimetic or peroxidase (POD) mimetic nanozymes have been extensively studied, their poor substrate selectivity significantly inhibits their practical applications. Nanozymes with specific biomolecules as substrates, especially ascorbic acid oxidase (AAO) mimetic nanozymes with ascorbic acid (AA) as a substrate, have scarcely been studied. Herein, inspired by the multi-Cu atom sites and the redox electron transfer pathway of Cu2+/Cu+ in the natural AAO, atomically dispersed Cu sites immobilized on N-doped porous carbon (Cu-N/C) are artificially designed to simulate the function of natural AAO. Compared with their natural counterparts, the Cu-N/C catalysts exhibited higher catalytic efficiency and superior stability. Combined theoretical calculation and experimental characterizations reveal that the Cu-N/C nanozymes could catalyze the AA oxidation through a 2e- oxygen reduction pathway with H2O2 as the product. Moreover, the Cu-N/C nanozymes also possess high POD activity. As a proof-of-concept application, Cu-N/C can simultaneously realize AA detection in fluorescent mode based on its AAO activity and total antioxidant capacity detection in colorimetric mode utilizing its POD activity.

In situ formed silicon-based nanoparticles enabled highly efficient dual-mode biosensing of chlorpyrifos.

Chlorpyrifos is widely used in agriculture but their residue is a threat to food safety and human health. The study aims to find an accurate and sensitive detection method for chlorpyrifos. Silicon-based nanoparticles (Si BNPs) with fluorescent and colorimetric dual signals are in-situ formed through the alkaline phosphatase (ALP) triggered reaction. The dual-mode sensor for chlorpyrifos can be facilely fabricated because the existence of chlorpyrifos would inhibit the activity of ALP and thus affect the production of Si BNPs. Under optimal condition, the fluorescence intensity and absorption intensity linearly correlate with the logarithm of chlorpyrifos concentration over wide range of 0.5-5000 ng/mL and 1-5000 ng/mL with low detection limit by the two detection modes, respectively. The dual-mode sensor is further applied to the detection of spiked chlorpyrifos in practical samples with satisfactory recovery, rendering it as a promising candidate to current methodologies for the simple and accurate detection of chlorpyrifos.

Self-deposited ultrasmall Ru nanoparticles on carbon nitride with high peroxidase-mimicking activity for the colorimetric detection of alkaline phosphatase.

Carbon nitride (C3N4) nanosheets are known as peroxidase mimics, but the low activity hinders their further application. Embedding active metal nanoparticles onto the C3N4 nanosheets is expected to break this limitation. Herein, highly dispersed ultrasmall Ru nanoparticles are anchored onto the C3N4 through spontaneous redox reaction. The as-obtained Ru-C3N4 exhibits excellent peroxidase-like activity, which can be further regulated by adjusting the loading of Ru nanoparticles on C3N4. Using Ru-C3N4 as a mimetic peroxidase, a colorimetric sensing method for alkaline phosphatase (ALP) detection is developed based on the inhibitory effect of ascorbic acid produced by hydrolysis of ALP and l-ascorbic acid 2-phosphate (AAP) on the color development reaction of TMB catalyzed by Ru-C3N4. The sensor exhibits wide linear range and low detection limit for the ALP sensing. Finally, the assay is applied to ALP detection in human serum and satisfactory results are obtained, which provides a promising strategy for colorimetric sensing of ALP.