Smartphone flashlight-triggered covalent organic framework nanozyme activity: A universal scheme for visual point-of-care testing

Most current redox-type nanozyme-based colorimetric sensing platforms are susceptible to interference from the reductant when using chromogenic probe, and the unstable H2O2 used in the peroxidase-like nanozyme-based systems is prone to difficulty in sensing signal reproducibility, while peroxidase-like nanozyme with oxidase-mimicking activity is easy to bring background interference by O2. Since the strong structural designability of covalent organic frameworks (COFs) endows them great application value in the sensing fields, therefore, we envision the construction a COF oxidase-like nanozyme-based controllable sensing system that integrates self-reporting, self-correcting and light-responsive functions to avoid these affects. Herein, 3-nitrotyrosine (3-NT) biomarker was selected as model analyte. 1,3,5-triformylphloroglucinol (Tp) and 3,6-diaminoacridine (DA) were acted as building monomers of the multifunctional COF nanozyme (termed as TpDA). Owing to the excellent light-responsive oxidase-mimicking property of TpDA, 3-NT can be efficiently oxidized, the inner filter effect (IFE) between TpDA and the 3-NT oxidation product greatly quenches the intrinsic fluorescence of TpDA, making it a controllable self-reporting system for fluorescence turn-off sensing 3-NT. Additionally, the excessive reactive oxygen species (ROS) that generated continuously during photocatalysis can resist the interference of endogenous reductants. This study not only provides new insights to avoid the interference of H2O2, background and reductants from conventional redox-type nanozyme-based colorimetric systems but also opens avenues to rational construct versatile COF nanozyme-based sensor.

Three-in-one covalent organic framework nanozyme: Self-reporting, self-correcting and light-responsive for fluorescence sensing 3-nitrotyrosine

Metal-organic frameworks (MOFs) have been widely used as nanozymes with a great development prospect due to their unique advantages. It is known that the current Fe-based or Cu-based MOF, etc., exhibits the catalytic activity of nanozymes through the Fenton catalytic reaction. And the conversion efficiency of the Fe3+/Fe2+ or Cu2+/Cu+ cycle is key to the catalytic activity. Therefore, we proposed a novel co-catalytic method to promote the reaction rate of the rate-limiting step of Cu2+/Cu+ conversion in the Fenton reaction of Cu2+/H2O2 to enhance the catalytic activity of the nanozymes. As a proof of concept, the MoCu-2MI nanozyme with high catalytic activity was successfully synthesized using Mo-doped Cu-2MI (2-methylimidazole). By using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, MoCu-2MI exhibited higher peroxidase-like activity than pure Cu-2MI. Then, it was confirmed that the newly introduced Mo played a crucial co-catalytic role by characterizing the possible catalytic mechanism. Specifically, Mo acted as a co-catalyst to accelerate the electron transfer in the system, and then promote the Cu2+/Cu+ cycle in the Cu-Fenton reaction, which was conducive to accelerating the production of a large number of reactive oxygen species (ROS) from H2O2, and finally improve the activity. Ultimately, a biosensor platform combined with MoCu-2MI and cholesterol oxidase realized the one-step colorimetric detection of cholesterol in the range of 2-140 μM with the detection limit as low as 1.2 μM. This study provides a new strategy for regulating the activity of MOF nanozymes.

Enhanced peroxidase-like activity of MOF nanozymes by co-catalysis for colorimetric detection of cholesterol.

Dipeptide Surface Modification and Ultrasound Boosted Phosphatase-Like Activity of the Ceria Nanozyme: Dual Signal Enhancement for Colorimetric Sensors

The successful combination of chemo- and enzyme catalysis technologies in wastewater treatment has presented great potentialities as well as challenges for decades. Herein, laccase (Lac) was immobilized on the Cu2[email protected] by covalent linkage to obtain a stable composite (Cu2[email protected]) with synergistic catalytic activity. The Cu2[email protected] with peroxidase-like activity was in situ synthesized by microwave-assisted assembly method. Cu2[email protected] exhibited high activity recovery, large immobilization capacity, remarkable tolerance to pH and high temperature conditions. Based on the prepared mimic multi-enzyme system, Cu2[email protected] showed broad application prospects in degradation and detection of phenolic compounds. The synergetic catalytic degradation efficiency reached 82.5% in 2h and the limit of detection (LOD) was 0.29 μM in the range of 0-200 μM of 2,4-dichlorophenol (2,4-DCP). Further investigation found that chemo- and enzyme catalysis jointly accelerate the degradation of 2,4-DCP, and the hydroxyl radical (•OH) mediated radical pathway serve a predominant role. Therefore, the chem-enzyme integrated catalyst presented in this work provides a promising platform for organic pollutants degradation and detection by combining the enzymes and Cu2[email protected] 

Biomimetic Laccase-Cu2O@MOF for synergetic degradation and colorimetric detection of phenolic compounds in wastewater

Colorimetric detection of creatinine based on specifically modulating the peroxidase-mimicking activity of Cu-Fenton system.

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Colorimetric detection of creatinine based on specifically modulating the peroxidase-mimicking activity of Cu-Fenton system.