Mesoporous Core-Shell Pd@Pt Nanospheres as Oxidase Mimics with Superhigh Catalytic Efficiency at Room Temperature

Single-atom Fe nanozymes with excellent oxidase-like and laccase-like activity for colorimetric detection of ascorbic acid and hydroquinone

Although traditional Fe-based nanozymes have shown great potential, generally only a small proportion of the Fe atoms on the catalyst's surface are used. Herein, we synthesized single-atom Fe on N-doped graphene nanosheets (Fe-CNG) with high atom utilization efficiency and a unique coordination structure. Active oxygen species including superoxide radicals (O2•-) and singlet oxygen (1O2) were efficiently generated from the interaction of the Fe-CNG with dissolved oxygen in acidic conditions. The Fe-CNG nanozymes were found to display enhanced oxidase-like and laccase-like activity, with Vmax of 2.07 × 10-7 M∙S-1 and 4.54 × 10-8 M∙S-1 and Km of 0.324 mM and 0.082 mM, respectively, which is mainly due to Fe active centers coordinating with O and N atoms simultaneously. The oxidase-like performance of the Fe-CNG can be effectively inhibited by ascorbic acid (AA) or hydroquinone (HQ), which can directly obstruct the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Therefore, a direct and sensitive colorimetric method for the detection of AA and HQ activity was established, which exhibited good linear detection and limit of detection (LOD) of 0.048 μM and 0.025 μM, respectively. Moreover, a colorimetric method based on the Fe-CNG catalyst was fabricated for detecting the concentration of AA in vitamin C. Therefore, this work offers a new method for preparing a single-atom catalyst (SAC) nanozyme and a promising strategy for detecting AA and HQ.

Trace Amount of Bi-Doped Core-Shell Pd@Pt Mesoporous Nanospheres with Specifically Enhanced Peroxidase-Like Activity Enable Sensitive and Accurate Detection of Acetylcholinesterase and Organophosphorus Nerve Agents

The urgent need for sensitive and accurate assays to monitor acetylcholinesterase (AChE) activity and organophosphorus pesticides (OPs) arises from the imperative to safeguard human health and protect the ecosystem. Due to its cost-effectiveness, ease of operation, and rapid response, nanozyme-based colorimetry has been widely utilized in the determination of AChE activity and OPs. However, the rational design of nanozymes with high activity and specificity remains a great challenge. Herein, trace amount of Bi-doped core-shell Pd@Pt mesoporous nanospheres (Pd@PtBi2) have been successfully synthesized, exhibiting good peroxidase-like activity and specificity. With the incorporation of trace bismuth, there is a more than 4-fold enhancement in the peroxidase-like performance of Pd@PtBi2 compared to that of Pd@Pt. Besides, no significant improvement of oxidase-like and catalase-like activities of Pd@PtBi2 was found, which prevents interference from O2 and undesirable consumption of substrate H2O2. Based on the blocking impact of thiocholine, a colorimetric detection platform utilizing Pd@PtBi2 was constructed to monitor AChE activity with sensitivity and selectivity. Given the inhibition of OPs on AChE activity, a biosensor was further developed by integrating Pd@PtBi2 with AChE to detect OPs, capitalizing on the cascade amplification strategy. The OP biosensor achieved a detection limit as low as 0.06 ng mL-1, exhibiting high sensitivity and anti-interference ability. This work is promising for the construction of nanozymes with high activity and specificity, as well as the development of nanozyme-based colorimetric biosensors.

Enhanced the intrinsic oxidase-like activity of chiral carbon dots via manganese doping for selective catalytic oxidation

It is highly desirable to design and construct chemical catalysts with high activity and specificity as the alternatives of natural enzymes for industrial application. Chiral carbon dots (CDs), possessing both the intrinsic enzyme-like activity and specific recognition ability, are one of good candidates for enzyme-like catalysts. However, their catalytic activity is far from that of natural enzymes and needs to be enhanced. In this work, the modulation of the chiral structure and catalytic activity of chiral CDs with intrinsic oxidase-like activity was implemented by manganese (Mn) doping. Under the light condition, chiral CDs (l-Ser-CDs and d-Ser-CDs) derived from chiral serine (Ser) show weak catalytic activity and low selectivity toward the oxidation of L type of dopamine (l-DOPA), whereas the Mn functionalized chiral CDs (l-Mn-CDs or d-Mn-CDs) exhibit 6.9 times higher in catalytic activity and 2.9 times in selectivity ratio (SR) than Ser-CDs. Mn-CDs involve two-path catalytic process, in which the photogenerated electrons could reduce O2 to O2- as the active species and the holes would oxidize DOPA directly. Moreover, doping of Mn enables the CDs to generate more O2-. Besides, l-Mn-CDs have higher catalytic activity than that of d-Mn-CDs (+54.2 %), and the chiral Mn-CDs have stronger selective adsorption capacity towards chiral DOPA than Ser-CDs. Our work provides a new method for designing and preparing novel chiral artificial enzymes.

RuCu Nanosheets with Ultrahigh Nanozyme Activity for Chemodynamic Therapy

Nanoenzymes have been widely explored for chemodynamic therapy (CDT) in cancer treatment. However, poor catalytic efficiency of nanoenzymes, especially in the tumor microenvironment with insufficient H2 O2 and mild acidity, limits the effect of CDT. Herein, a new ultrathin RuCu nanosheet (NS) based nanoenzyme which has a large specific surface area and abundant channels and defects is developed. The RuCu NSs show superb catalytic efficiency for the oxidation of peroxidase substrate H2 O2 at a wide range of pH and their catalytic efficiency (kcat /Km = 177.2 m-1  s-1 ) is about 14.9 times higher than that of the single-atom catalyst FeN3 P. Besides being an efficient nanozyme as peroxidase, the RuCu NSs possess other two enzyme activities, not only disproportionating superoxide anion to produce H2 O2 but also consuming glutathione to keep a high concentration of H2 O2 in the tumor microenvironment for Fenton reaction. With these advantages, the RuCu NSs exhibit good performance to kill cancer cells and inhibit tumor growth in mice, demonstrating a promising potential as new CDT reagent.

Synthesis of L-aspartic acid-based bimetallic hybrid nanoflowers to immobilize snailase for the production of rare ginsenoside compound K

The conversion of the common ginsenoside Rb1 to the rare ginsenoside compound K (CK) using snailase (Sna) is an efficient method for industrial production. In order to improve the stability and recoverability of Sna during the catalytic conversion of ginsenosides, the cage-like immobilised Sna material ZIF-ZnCo-Sna and the hybrid nanoflower-based immobilised Sna material Asp@ZIF-ZnCo-Sna modified with L-aspartic acid (Asp) were synthesised using a one-step method. The addition of Asp provides a richer ligand pattern and the morphology of the material changed from a cage to a hybrid nanoflower. The modified hybrid nanoflower Asp@ZIF-ZnCo-Sna has a larger specific surface area, resulting in an enzyme loading of 142.57 mg g^-1. The more abundant mesopores allowed the enzyme to maintain a good conformation and the enzyme activity was 79.8% of that of the free Sna. In addition, the total conversion rate of Asp@ZIF-ZnCo-Sna to ginsenoside Rb1 was as high as 88.35%, whereas that of ZIF-ZnCo-Sna was 79.12%. Moreover, after 6 cycles, the catalytic conversion of ZIF-ZnCo-Sna and Asp@ZIF-ZnCo-Sna and the crystalline shape remained the same, indicating that both composites have good stability and catalytic properties. This new approach of improving the MOF morphology and enzymatic activity by a one-step addition of small biological molecules provides a simple, rapid, and effective strategy for biocatalysis. It also provides a certain reference value for the immobilized Sna to produce rare ginsenoside CK.

Structure design mechanisms and inflammatory disease applications of nanozymes

Nanozymes are artificial enzymes with high catalytic activity, low cost, and good biocompatibility, and have received ever-increasing attention in recent years. Various inorganic and organic nanoparticles have been found to exhibit enzyme-like activities and are used as nanozymes for diverse biomedical applications ranging from tumor imaging and therapeutics to detection. However, their further clinical applications are hindered by the potential toxicity and long-term retention of nanomaterials in vivo. Clarifying the catalytic mechanism of nanozymes and identifying the key factors responsible for their behavior can guide the design of nanozyme structure, enlighten the ways to improve their enzyme-like activities, and minimize the dosage of nanozymes, leading to reduced toxicity to the human body for a real biomedical application prospect. In particular, inflammation occurring in numerous diseases is closely related to reactive oxygen species, and the active oxygen scavenging ability of nanozymes potentially exerts excellent therapeutic effects on inflammatory diseases. In this review, we systematically summarize the structure-activity relationship of nanozymes, including regulation strategies for size and morphology, surface structure, and composition. Based on the structure-activity mechanisms, a series of chemically designed nanozymes developed to target various inflammatory diseases are briefly summarized.