Abstract
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.
Highlights
Through the screening of catalytic activity by the typical colorimetric reaction, we found that CoAC has significantly high peroxidase-like activity and applied them to develop fluorescent biosensor for the sensitive determination of H2 O2 and glucose concentrations
No significant fluorescence intensity is observed in the negative control samples where carbohydrate molecules similar to the target glucose are used even at tenfold higher concentrations. These results demonstrate that a specific fluorescent reaction of only the target glucose is promoted by the CoAC-based system
The results show that the presence of serum had negligible effect and did not induce any significant changes (
Summary
3-aminopropyl-functionalized magnesium phyllosilicate (i.e., Mg-aminoclay [MgAC], formulated as [H2 N(CH2 )3 ]8 Si8 Mg6 O12 (OH)4 ) was developed by one-pot sol–gel reaction under ambient conditions by Mann et al [6,7] showing unique interactions of organic-pendants with cell or other molecules [8,9]. In biomedical fields, as well as with heavy metals [10] in environmental applications. This aminoclay structure is composed of tetrahedral brucite (MgO) in the middle, sandwiched by octahedral silica (SiO2 ) as the unit structure in the vertical direction (i.e., 2:1 trioctahedral clay) and a repeated tetrahedral/octahedral structure in pairs, known as the 1:1 dioctahedral structure. The protonated clusters of MgAC with positively charged zeta potential in the wide pH range of
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