The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201906641. Development of high-performance carbon dots (CDs) with emission wavelength longer than 660 nm (deep red emission) is critical in deep-tissue bioimaging, yet it is still a major challenge to obtain CDs with both narrow full width at half maximum (FWHM) and high deep red/ near-infrared emission yield. Here, deep red emissive carbonized polymer dots (CPDs) with unprecedented FWHM of 20 nm are synthesized. The purified CPDs in dimethyl sulfoxide (DMSO) solution possess quantum yield (QY) as high as 59% under 413 nm excitation, as well as recorded QY of 31% under 660 nm excitation in the deep red fluorescent window. Detailed characterizations identify that CPDs have unique polymer characteristics, consisting of carbon cores and the shells of polymer chains, and π conjugated system formed with N heterocycles and aromatic rings governs the single photoluminescence (PL) center, which is responsible for high QY in deep red emissive CPDs with narrow FWHM. The CPDs exhibit strong absorption and emission in the deep red light region, low toxicity, and good biocompatibility, making them an efficient probe for both one-photon and two-photon bioimaging. CPDs are rapidly excreted via the kidney system and hepatobiliary system.
Recently, in situ detection of hydrogen peroxide (H 2 O 2 ) generated from live cells have caused tremendous attention, because it is of great significance in the control of multiple biological processes. Herein, Fe−N−C single-atom nanozymes (Fe−N−C SAzymes) with intrinsic peroxidase-like activity were successfully prepared via high-temperature calcination using FeCl 2 , glucose, and dicyandiamide as precursors. The Fe−N−C SAzymes with FeN x as active sites were similar to natural metalloproteases, which can specifically enhance the peroxidase-like activity rather than oxidase-like activity. Accordingly, owing to the excellent catalytic efficiency of the Fe−N−C SAzymes, colorimetric biosensing of H 2 O 2 in vitro was performed via a typical 3,3′,5,5′-tetramethylbenzidine induced an allochroic reaction, demonstrating the satisfactory specificity and sensitivity. With regard to the practical application, in situ detection of H 2 O 2 generated from the Hela cells by the Fe−N−C SAzymes was also performed, which can expand the applications of the newborn SAzymes.
Despite the breakthroughs of transition-metal catalysts in enzyme mimicking, fundamental investigation on the design of efficient nanozymes at the atomic scale is still required for boosting their intrinsic activities to fill in gaps from enzymes to nanozymes. Herein, we developed a universal salt-template strategy for the fabrication of atomically dispersed Fe atoms on ultrathin nitrogen-doped carbon nanosheets characterized by a dramatically high concentration of 13.5 wt %. The proposed Fe-N-C nanozymes with densely isolated FeN 4 sites show high peroxidase-like activities and exhibit a specific activity of 25.33 U/mg, superior to Zn(Co)-N-C nanozymes. Both experiments and theoretical analysis revealed that FeN 4 sites not only lead to the strong adsorption of H 2 O 2 molecules but also weaken the bonding interaction between single Fe atom and two absorbed hydroxyl groups, lowering the energy barrier of the formation of hydroxyl radicals and therefore boosting their peroxidase-like activities. As expected, utilizing the peroxidase-like activity of Fe-N-C nanozymes, good sensitivity and selectivity for the intracellular H 2 O 2 monitoring were realized. It offers a versatile approach for the construction of densely isolated M-N-C single-atom catalysts and achieves better understanding of single sites for the peroxidase-like catalytic mechanisms.
Single‐atom catalysts (SACs) have attracted extensive attention in the catalysis field because of their remarkable catalytic activity, gratifying stability, excellent selectivity, and 100% atom utilization. With atomically dispersed metal active sites, Fe‐N‐C SACs can mimic oxidase by activating O2 into reactive oxygen species, O2−• radicals. Taking advantages of this property, single‐atom nanozymes (SAzymes) can become a great impetus to develop novel biosensors. Herein, the performance of Fe‐N‐C SACs as oxidase‐like nanozymes is explored. Besides, the Fe‐N‐C SAzymes are applied in biosensor areas to evaluate the activity of acetylcholinesterase based on the inhibition toward nanozyme activity by thiols. Moreover, this SAzymes‐based biosensor is further used for monitoring the amounts of organophosphorus compounds.
Nanozyme/natural enzyme hybrid plays a vital role in biosensing, therapy, and catalysis owing to the integrated advantages in the selectivity of natural enzymes and controllable catalytic activity of nanozymes. Herein, Fe-MIL-88B-NH2 [(Fe-metal–organic framework (MOF)] with remarkable peroxidase-like activity, ultrahigh stability, and high biocompatibility was utilized for immobilization of glucose oxidase (GOx) via an amidation coupling reaction. On the basis of the excellent selectivity and catalytic activity of Fe-MOF-GOx, a cascade catalysis was performed for the colorimetric detection of glucose. The integrated Fe-MOF-GOx not only exhibited higher stability and reusability than their mixtures including Fe-MOF and free GOx system but also possessed a wide linear range (1–500 μM), with a low detection limit of 0.487 μM for glucose detection.
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