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In this study, we describe a novel peroxidase-like activity of Co-aminoclay [CoAC] present at pH ~5.0 and its application to fluorescent biosensor for the determination of H2O2 and glucose. It is synthesized with aminoclays (ACs) entrapping cationic metals such as Fe, Cu, Al, Co., Ce, Ni, Mn, and Zn to find enzyme mimicking ACs by sol–gel ambient conditions. Through the screening of catalytic activities by the typical colorimetric reaction employing 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)diammonium salt (ABTS) as a substrate with or without H2O2, Fe, Cu, and CoACs are found to exhibit peroxidase-like activity, as well as oxidase-like activity was observed from Ce and MnACs. Among them, CoAC shows exceptionally high peroxidase-like activity, presumably due to its ability to induce electron transfer between substrates and H2O2. CoAC is then used to catalyze the oxidation of Amplex® UltraRed (AUR) into a fluorescent end product, which enables a sensitive fluorescent detection of H2O2. Moreover, a highly sensitive and selective glucose biosensing strategy is developed, based on enzyme cascade reaction between glucose oxidase (GOx) and CoAC. Using this strategy, a highly linear fluorescence enhancement is verified when the concentration of glucose is increased in a wide range from 10 μM to 1 mM with a lower detection limit of 5 μM. The practical diagnostic capability of the assay system is also verified by its use to detect glucose in human blood serum. Based on these results, it is anticipated that CoAC can serve as potent peroxidase mimetics for the detection of clinically important target molecules.

Cerium oxide nanoparticles, also called nanoceria, have recently gained much attention as oxidase-mimicking nanozymes that catalyze the oxidation of chromogenic substrates for color generation without the addition of H2O2. Herein, we have developed a unique colorimetric biosensor for thrombin in human blood plasma, which relies on thrombin-binding aptamer (TBA)-mediated inhibition of the oxidase activity of nanoceria and its restoration by very selective interactions of TBA with target thrombin. In this system, nanoceria were first incubated with TBA, resulting in quick reduction of the oxidase activity of nanoceria via the adsorption of single-stranded (ss)DNA-type TBA on nanoceria. By the addition of sample solutions containing target thrombin, TBA bound on the nanoceria would strongly interact with free thrombin and be detached from the nanoceria, thereby increasing the available surface area of the nanoceria and consequently enhancing the oxidase activity. Using this strategy, target thrombin was successfully detected at concentrations as low as 100 pM over a wide linear range from 0.1 to 10 nM. The diagnostic capability of this method has been demonstrated by detecting thrombin in human blood plasma, showing its great potential in the practical applications.

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Included angles (α) have vital effect on the flow and heat transfer in cross-corrugated triangular ducts. The friction factor and Nusselt number were estimated at different Reynolds numbers from both experiments and simulations. Results show that the flow in the duck with α=90 has the largest friction factor and Nusselt number. However, the included angle influences the flow and heat transfer in cross-corrugated triangular ducts in different ways. The field synergy principle was used to explore the mechanism of the different impacts of the included angle. Results show that the flow in the cross-corrugated triangular duct with α=90o has the smallest domain averaged included angle (βm), which implies the best synergy performance. The results of the field synergy principle were also validated by analyzing the performance evaluation criterion and studying the velocity vector and temperature distributions