| Natural enzymes are proteins that catalyze chemical reactions, which have been successfully used for many different targets in various fields. Relative to chemical catalysts, enzymes possess remarkable merits(e.g., high substrate specificity and high catalytic activity). Unfortunately, natural enzymes are easily denatured by environmental change and can be digested by protease. In addition, high cost and rigorous storage conditions also limit their applications. Thus, developing stable enzyme mimetics is highly appealing. Recently, some nanomaterials, such as ferromagnetic nanoparticles, noble metal nanoparticles, graphene oxide and rare earth nanoparticles, have been found to possess unique enzyme–mimicking catalytic activities. Compared with natural enzymes, nanomaterials based enzyme mimetics possess some merits including stable against denaturing, high catalytic activity, low in cost, and easy to store. So, nanomaterials are promising candidates as enzyme mimetics.(1) We found that the bovine serum albumin(BSA) stabilized red or blue emitting gold nanoclusters(Au NCs) exhibited enzyme–like activity under visible light irradiation. The BSA–Au NCs had better stability against stringent conditions compared to natural enzyme. In addition, the photostimulated enzyme mimetics of BSA–Au NCs showed several unprecedented advantages over natural peroxidase or other existing alternatives based on nanomaterials, such as the independence of hydrogen peroxide on activity and the easily regulated activity by light irradiation. The mechanism of the photoresponsive enzyme–like activity of BSA–Au NCs was investigated. The photoactivated BSA–Au NCs was designed to develop a facile, cheap, and rapid colorimetric assay to detect trypsin through trypsin digestion of the protein template of BSA–stabilized Au NCs. The limit of detection for trypsin was 0.6 μg/m L, which was much lower than the average level of trypsin in patient’s urine or serum.(2) A novel colorimetric biosensor for Hg2+ and DNA molecules is presented based on Hg2+ stimulated oxidase–like activity of bovine serum albumin protected silver clusters(BSA–Ag NCs). Under mild conditions, Hg2+ activated BSA–Ag NCs to show high catalytic activity toward the oxidation of 3, 3’, 5, 5’–tetramethylbenzidine(TMB) using ambient dissolved oxygen as an oxidant. The oxidase–like activity of BSA–Ag NCs was “switched–on” selectively in the presence of Hg2+, which permitted a novel and facile colorimetric sensor for Hg2+. As low as 25 nmol/L Hg2+ could be detected with a linear range from 80 nmol/L to 50 mmol/L. In addition, by coupling the Hg2+ switched–on the oxidase–mimicking activity of BSA–Ag NCs, we developed a novel label–free strategy for facile and fast colorimetric detection of DNA molecules. Compared with other methods, this method presents several advantages such as the independence of hydrogen peroxide, high sensitivity and good selectivity, avoiding any modification or immobilization of DNA, which holds a great potential of metal NCs for clinical application in biosensing and biotechnology.(3) Catechol(CA) modified Ti O2 could obviously catalyze the oxidation of TMB under visible light irradiation(λ≥400 nm). Kinetic analysis indicates that the activity of Ti O2–CA showed the typical Michaelis-Menten kinetics and good affinity for TMB, which is superior to HRP in the same conditions. At the same time, the catalytic mechanism was found for the enzyme–like activity of Ti O2–CA under visible–light irradiation, the superoxide anions(O2?-) and hydroxyl radicals(?OH) are main reactive species responsible for TMB oxidation. Importantly, the activity of this oxidase mimetics using oxygen(not relied on destructive hydrogen peroxide) as a mild and green electron acceptor. We have proposed a new type of colorimetric assay for the detection of ALP activity, ALP inhibitors and immunoassay based on photoactivated Ti O2–CA. Furthermore, the developed method was facile, sensitive and fast, indicating its prospect in high–throughput biomedical sensing. |
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