Carbon Nanozymes Research Articles

Chromium decorated leaf-like N-doped carbon anchoring with active Cr-Nx sites as oxidase mimics for isoniazid sensing

Research about constructing transition metal-based N-doped carbon nanozymes with high-performance for sensing applications has attracted great attention. Here, a novel Cr decorated N-doped carbon (Cr-NC) derived from zeolite imidazolate framework-leaf with unique Cr-Nx active sites was developed via pyrolysis strategy. The nanosheet structure endowed Cr-NC with highly exposed active sites for promoting O2 adsorption and cleavage into reactive OH, O2− and 1O2, for oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB), showing oxidase-like activity. Compared with that of N-doped carbon (NC), the catalytic activity of Cr-NC oxidase mimic was increased by 19.55 times. Cr species doping in carbon matrix could promote electron transfer ability of Cr-NC and Cr-Nx anchoring in Cr-NC was the major active sites in improving the oxidase-like performance of NC. The Cr-NC displayed a good affinity to TMB and a fast reaction velocity, showing the Km value of 0.54 mM and the Vmax of 3.03 × 10−7 M/s. Since isoniazid (INH) contains hydrazine groups, which inhibits the oxidation of TMB, a sensitive and highly selective assay for INH was established based on the oxidase-like activity of Cr-NC. The linear response of the detection platform to INH ranges from 0.25 to 50 μM with the detection limit (3σ/k) of 0.22 μM and the relative standard deviation (RSD, n = 3) less than 3.5%. The platform has been successfully applied to the determination of INH in real pharmaceutical preparations.

A multifunctional cascade nanoreactor based on Fe-driven carbon nanozymes for synergistic photothermal/chemodynamic antibacterial therapy.

Healing bacterial chronic wounds caused by hyperglycemia is of great significance to protect the physical and mental health of diabetic patients. In this context, emerging chemodynamic therapy (CDT) and photothermal therapy (PTT) with broad antibacterial spectra and high spatiotemporal controllability have flourished. However, CDT was challenged by the near-neutral pH and inadequate H2O2 surrounding the chronic wound site, while PTT showed overheating-triggered side effects (e.g., damaging the normal tissue) and poor effects on thermotolerant bacterial biofilms. Therefore, we engineered an all-in-one glucose-responsive photothermal nanozyme, GOX/MPDA/Fe@CDs, consisting of glucose oxidase (GOX), Fe-doped carbon dots (Fe@CDs), and mesoporous polydopamine (MPDA), to efficiently treat chronic diabetic wound bacterial infections and eradicate biofilms without impacting the surrounding normal tissues. Specifically, GOX/MPDA/Fe@CDs produced a local temperature (∼ 45.0°C) to enhance the permeability of the pathogenic bacterium and its biofilm upon near-infrared (NIR) 808 nm laser irradiation, which was seized to initiate endogenous high blood glucose to activate the catalytic activity of GOX on the GOX/MPDA/Fe@CD surface to achieve the simultaneous self-supplying of H2O2 and H+, cascade catalyzing •OH production via a subsequent peroxidase-mimetic activity-induced Fenton/Fenton-like reaction. As such, the in vivo diabetic wound infected with methicillin-resistant Staphylococcus aureus was effectively healed after 12.0 days of treatment. This work was expected to provide an innovative approach to the clinical treatment of bacterially infected diabetic chronic wounds. STATEMENT OF SIGNIFICANCE: An all-in-one glucose-responsive photothermal nanozyme GOX/MPDA/Fe@CDs was constructed. Cascade nanozyme GOX/MPDA/Fe@CDs self-supply H2O2 and H+ to break H2O2 and pH limits to fight bacterial infections. Synergistic chemotherapy and photothermal therapy with nanozyme GOX/MPDA/Fe@CDs accelerates healing of biofilm-infected diabetic wounds.

Specific detection of fungicide thiophanate-methyl: A smartphone colorimetric sensor based on target-regulated oxidase-like activity of copper-doped carbon nanozyme

Nanozyme-based colorimetric assays have shown great potential in the rapid and sensitive determination of pesticide residue in environment. However, the non-specific enzyme inhibition makes the assays generally lack of selectivity. In this study, we proposed a colorimetric sensing platform for the specific detection of the agricultural fungicide thiophanate-methyl (TM) based on its distinctive inhibitory effect on the nanozyme activity. Since TM contains the symmetric ethylenediamine- and bisthiourea-like groups, it displays strong affinity to the metal site, leading to a loss of the catalytic activity. Accordingly, a Cu-doped carbon nanozyme with excellent oxidase-like properties was designed, and the oxidation process of chromogenic substrate is promoted by Cu-induced generation of reactive oxygen species. Interestingly, the nanozyme activity can be directly and strongly restrained by TM, rather than other probably coexistent pesticides. Consequently, the as-proposed analytical method exhibits specific response toward TM and good linear relationship in the range of 0.2–15 μg mL−1 with a low limit of detection of 0.04 μg mL−1 (S/N = 3). Besides, a smartphone-assisted rapid detection was achieved through identifying the RGB value of the chromogenic system. This work provides a new nanozyme inhibition strategy for the specific detection of TM in environmental sample.

Oxidation of Hydrogen Sulfide to Polysulfide and Thiosulfate by a Carbon Nanozyme: Therapeutic Implications with an Emphasis on Down Syndrome.

Hydrogen sulfide (H2 S) is a noxious, potentially poisonous, but necessary gas produced from sulfur metabolism in humans. In Down Syndrome (DS), the production of H2 S is elevated and associated with degraded mitochondrial function. Therefore, removing H2 S from the body as a stable oxide could be an approach to reducing the deleterious effects of H2 S in DS. In this report we describe the catalytic oxidation of hydrogen sulfide (H2 S) to polysulfides (HS2+n - ) and thiosulfate (S2 O3 2- ) by poly(ethylene glycol) hydrophilic carbon clusters (PEG-HCCs) and poly(ethylene glycol) oxidized activated charcoal (PEG-OACs), examples of oxidized carbon nanozymes (OCNs). We show that OCNs oxidize H2 S to polysulfides and S2 O3 2- in a dose-dependent manner. The reaction is dependent on O2 and the presence of quinone groups on the OCNs. In DS donor lymphocytes we found that OCNs increased polysulfide production, proliferation, and afforded protection against additional toxic levels of H2 S compared to untreated DS lymphocytes. Finally, in Dp16 and Ts65DN murine models of DS, we found that OCNs restored osteoclast differentiation. This new action suggests potential facile translation into the clinic for conditions involving excess H2 S exemplified by DS.

Oxidized Activated Charcoal Nanozymes: Synthesis, and Optimization for In Vitro and In Vivo Bioactivity for Traumatic Brain Injury.

Carbon-based superoxide dismutase (SOD) mimetic nanozymes have recently been employed as promising antioxidant nanotherapeutics due to their distinct properties. The structural features responsible for the efficacy of these nanomaterials as antioxidants are, however, poorly understood. Here, the process-structure-property-performance properties of coconut-derived oxidized activated charcoal (cOAC) nano-SOD mimetics are studied by analyzing how modifications to the nanomaterial's synthesis impact the size, as well as the elemental and electrochemical properties of the particles. These properties are then correlated to the in vitro antioxidant bioactivity of poly(ethylene glycol)-functionalized cOACs (PEG-cOAC). Chemical oxidative treatment methods that afford smaller, more homogeneous cOAC nanoparticles with higher levels of quinone functionalization show enhanced protection against oxidative damage in bEnd.3 murine endothelioma cells. In an in vivo rat model of mild traumatic brain injury (mTBI) and oxidative vascular injury, PEG-cOACs restore cerebral perfusion rapidly to the same extent as the former nanotube-derived PEG-hydrophilic carbon clusters (PEG-HCCs) with a single intravenous injection. These findings provide a deeper understanding of how carbon nanozyme syntheses can be tailored for improved antioxidant bioactivity, and set the stage for translation of medical applications.

A DNA‐Gated and Self‐Protected Bioorthogonal Catalyst for Nanozyme‐Assisted Safe Cancer Therapy

AbstractTransition metal catalysts (TMCs) mediated bioorthogonal uncaging catalysis has sparked increasing interest in prodrug activation. However, due to their “always‐on” catalytic activity as well as the complex and catalytic‐detrimental intracellular environment, the biosafety and therapeutic efficiency of TMCs are unsatisfactory. Herein, a DNA‐gated and self‐protected bioorthogonal catalyst has been designed by modifying nanozyme‐Pd0 with highly programmable nucleic acid (DNA) molecules to achieve efficient intracellular drug synthesis for cancer therapy. Monolayer DNA molecules could endow the catalyst with targeting and perform as a gatekeeper to achieve selective prodrug activation within cancer cells. Meanwhile, the prepared graphitic nitrogen‐doped carbon nanozyme with glutathione peroxidase (GPx) and catalase (CAT)‐like activities could improve the catalytic‐detrimental intracellular environment to prevent the catalyst from being inactivated and sensitize the subsequent chemotherapy. Overall, we believe that our work will promote the development of secure and efficient bioorthogonal catalytic systems and provide new insights into novel antineoplastic platforms.

A DNA-Gated and Self-Protected Bioorthogonal Catalyst for Nanozyme-Assisted Safe Cancer Therapy.

Transition metal catalysts (TMCs) mediated bioorthogonal uncaging catalysis has sparked increasing interest in prodrug activation. However, due to their "always-on" catalytic activity as well as the complex and catalytic-detrimental intracellular environment, the biosafety and therapeutic efficiency of TMCs are unsatisfactory. Herein, a DNA-gated and self-protected bioorthogonal catalyst has been designed by modifying nanozyme-Pd0 with highly programmable nucleic acid (DNA) molecules to achieve efficient intracellular drug synthesis for cancer therapy. Monolayer DNA molecules could endow the catalyst with targeting and perform as a gatekeeper to achieve selective prodrug activation within cancer cells. Meanwhile, the prepared graphitic nitrogen-doped carbon nanozyme with glutathione peroxidase (GPx) and catalase (CAT)-like activities could improve the catalytic-detrimental intracellular environment to prevent the catalyst from being inactivated and sensitize the subsequent chemotherapy. Overall, we believe that our work will promote the development of secure and efficient bioorthogonal catalytic systems and provide new insights into novel antineoplastic platforms.

Novel carbon nanozymes with enhanced phosphatase-like catalytic activity for antimicrobial applications

In this work, Sulfur and Nitrogen co-doped carbon nanoparticles (SN-CNPs) were synthesized by hydrothermal method using dried beet powder as the carbon source. TEM and AFM images indicated that these SN-CNPs form a round-shape ball with an approximate diameter of 50 nm. The presence of Sulfur and Nitrogen in these carbon-based nanoparticles was confirmed by FTIR and XPS analyses. These SN-CNPs were found to have strong phosphatase-like enzymatic activity. The enzymatic behavior of SN-CNPs follows the Michaelis–Menten mechanism with greater vmax and much lower Km values compared to alkaline phosphatase. Their antimicrobial properties were tested on E. coli and L. lactis, with MIC values of 63 μg mL−1 and 250 μg mL−1, respectively. SEM and AFM images of fixed and live E. coli cells revealed that SN-CNPs strongly interacted with the outer membranes of bacterial cells, significantly increasing the cell surface roughness. The chemical interaction between SN-CNPs and phospholipid modeled using quantum mechanical calculations further support our hypothesis that the phosphatase and antimicrobial properties of SN-CNPs are due to the thiol group on the SN-CNPs, which is a mimic of the cysteine-based protein phosphatase. The present work is the first to report carbon-based nanoparticles with strong phosphatase activity and propose a phosphatase natured antimicrobial mechanism. This novel class of carbon nanozymes has the potential to be used for effective catalytic and antibacterial applications.Graphical abstract

Carbon nanosphere based bifunctional oxidoreductase nano-catalytic agent to mitigate hypoxia in cancer cells

Developing metal-free carbon nanozyme for tumor hypoxia is difficult. In biomedical applications, especially in the case of biomolecular detection, extensive research has been done on nanozymes with enzyme-mimicking catalytic activity. However, there are considerably fewer investigations on targeted nano-catalytic tumor therapy. Nano catalytic medicine-enabled chemotherapy is a safe and promising treatment strategy that involves the conversion of excess H2O2 into O2 in a tumor environment. Here we have synthesized carbon nanosphere (CNS) using the Camellia sinensis plant (CS-CNS). Further surface functionalization was achieved via nitrilotriacetic acid conjugation (NTA@CS-CNS). A stability study of synthesized nanozyme in the presence of various cations, anions, and 5 different pH range suggested the robustness of carbon based nanoassembly. The catalytic in vitro study shows that NTA@CS-CNS mimics peroxidase and catalase using TMB and H2O2 as substrates. NTA@CS-CNS showed Km and Vmax values of ~ 193.2 μM and 0.43 μM/s, ~ 413 μM and 1.42 μM/s, and ~ 378 μM and 1.63 μM/s, respectively when H2O2 and TMB was used for CAT and POD activity. Results showed that NTA@CS-CNS in combination with SFN and laser irradiation reduces hypoxia. Hence, our study could pave the path for the development of different non-toxic nano catalytic therapy for tumors in cancerous cells.

Multi‐Functional Carbon Dots for Visualizing and Modulating ROS‐Induced Mitophagy in Living Cells

AbstractReactive oxygen species (ROS)‐induced mitophagy is associated with a variety of diseases. Therefore, visualizing and modulating the process of ROS‐induced mitophagy is essential for understanding the role of mitophagy in cellular homeostasis, physiological processes, and pathogenesis. Herein, using fluorescence lifetime imaging microscopy (FLIM), for the first time the complete dynamic process of PINK1/Parkin pathway‐mediated mitophagy is described. Induced by the photo‐controlled release of ROS, nitrogen‐doped multi‐functional carbon nanozymes (ENZ‐NCDs) is used as a probe to visualize and quantitatively study ROS‐induced mitophagy. The successful preparation of ENZ‐NCDs provides a potentially powerful tool and a new strategy for real‐time mitophagy monitoring and future quantification of mitochondrial damage caused by ROS and ROS‐induced mitophagy‐related diseases.

Cobalt Single-Atom Nanozyme Co-Administration with Ascorbic Acid Enables Redox Imbalance for Tumor Catalytic Ablation.

The elevated antioxidant defense system in cancer cells can lead to resistance to treatments involving ROS. Breaking the redox balance of the cell system through a "open up the source and regulate the flow" strategy can inhibit the growth of cancer cells and thus design a cancer treatment strategy. Here, cobalt single atom-supported N-doped carbon nanozymes (Co SA-N/C) were synthesized via a simple sacrificial template method, which can mimic the properties of ascorbate oxidase and glutathione oxidase effectively. The synthesized Co SA-N/C can induce the generation of active oxygen by accelerating the oxidation of ascorbic acid (AA) and destroy the endogenous active oxygen scavenging system by consuming the main antioxidant, glutathione (GSH). In-depth in vitro and in vivo investigations indicate that compared with solo therapy, Co SA-N/C together with AA can significantly enhance the anti-tumor efficiency by simultaneously elevating oxidative stress and consuming the overexpressed glutathione (GSH) through the redox reaction catalyzed by Co SA-N/C. This work provides a promising route for developing nanozyme-guided and ascorbate-based antitumor agents.

Visual evaluation of acetylcholinesterase inhibition by an easy-to-operate assay based on N-doped carbon nanozyme with high stability and oxidase-like activity.

Acetylcholinesterase (AChE) is the key enzyme associated with neurotransmission, and thus many drugs have been explored for their inhibitory effect on AChE, such as donepezil for Alzheimer's disease and organophosphorus pesticides (OPs). Compared with clinical trials, in vitro screening bioassays for AChE inhibitors are preferable in terms of operability and cost. Herein, we developed an easy-to-operate nanozyme-based colorimetric assay for the evaluation of AChE inhibitory strength with excellent anti-interference ability and low dependence on professional equipment. The metal-free carbon nanozyme NC900 played an important role in the signal output due to its features of efficient oxidase-like activity, excellent water dispersibility, high stability and low color interference. Employing various AChE-targeted or non-targeted pesticides as examples, the as-proposed assay exhibited excellent distinguishing ability for different chemicals. The higher absorption intensity at 652 nm represents a stronger inhibitory effect, as well as blue color. In addition, this method was used to study the influence of pH on the degradation of prodrugs, and the efficiency of mixed pesticides. This work provides a simple and reliable assay to screen AChE inhibitors, which is promising for the preliminary evaluation of a large number of potential candidates.

Nonmetallic N/C Nanozyme Performs Continuous Consumption of Glu for Inhibition of Colorectal Cancer Cells.

Colorectal cancer (CRC) is the third leading cause of cancer-related mortality. 5-Fluorouracil (5-FU) is the first choice for treatment of CRC, but it cannot avoid the negative effects from local high glucose (Glu) in tumor. Recently, 5-FU therapy has been combined with other treatment modalities for CRC synergistic therapy. Although these combination therapy strategies are more effective in cancer therapy, the toxicity side effects to the liver and cause metabolic acidosis still exist. Herein, we report an emerging amorphous honeycomb-like nitrogen-doped carbon (N/C) nanozyme with nicotinamide adenine dinucleotide (NADH) oxidase and catalase (CAT) activity and cascade it with natural glucose dehydrogenase (GDH) to realize NAD+ regeneration and further hyperglycemia management. In this case, by the coupling of N/C nanozyme with natural GDH to form a N/C-GDH system, the electron transfer route can switch from Glu to a common but limited electron receptor, i.e., NAD+ to ubiquitous large amounts of oxygen, achieving the purpose of sustainable consumption of Glu under NAD+ circulation and regeneration, and importantly escaping the generation of toxic H2O2. The combination of the N/C-GDH system and 5-FU on CRC cells was investigated to assess their synergistic bioeffects. Notably, our results showed that the N/C-GDH system and 5-FU in combination significantly suppress the proliferation of human colon cancer cells (HCT-116) by reducing the sugar level and induced apoptosis compared with either material or drug used alone. This work expands the nanozymes in blood Glu management as well as the promising cancer cell inhibition and provides the possibility of nonmetallic nanomaterials in the realization of effective treatment of cancer.

Metal-Free Carbon Nanozyme as Nicotinamide Adenine Dinucleotide Oxidase Mimic over a Broad pH Range for Coenzyme Regeneration

Exploration of high-performance nanozymes for specific biomolecules is crucial but challenging for practical application. Nicotinamide adenine dinucleotide (NADH) oxidase can drive efficient regeneration of the oxidized coenzyme NAD+, which is of great significance for numerous NAD+-dependent biocatalytic pathways. However, issues including its instability and incompatibility with tandem enzymes in terms of pH, temperature, etc. remain to be addressed. Here, we report nitrogen-doped carbon materials templated from g-C3N4 with NOX-like behaviors. The model s-NC nanozyme displays excellent catalytic activity in a wide pH range of 5.0–10.0 and a remarkable specific activity of up to 3.2 U/mg, which is superior to those of the reported NOX mimics. Furthermore, s-NC is coupled with natural dehydrogenases to develop a nanozyme–enzyme hybridization model for biosynthesis. Notably, it can well meet the pH requirement of the dehydrogenase under alkaline medium. This work not only develops NOX-mimicking metal-free nanozymes but also has inspired significance toward NAD+-mediated biosynthesis using artificial nanozymes.

Colorimetric Analysis of Captopril on the Basis of Its Free Radical Scavenger Character with Carbon Nanozymes as Catalyst

Colorimetric Analysis of Captopril on the Basis of Its Free Radical Scavenger Character with Carbon Nanozymes as Catalyst

Boron-Doped and Ketonic Carbonyl Group-Enriched Graphdiyne as a Dual-Site Carbon Nanozyme with Enhanced Peroxidase-Like Activity.

We demonstrate the preparation of a dual-site carbon nanozyme, boron-doped and ketonic carbonyl (-C=O) group-enriched graphdiyne (B-GDY), with an enhanced peroxidase-like activity. Taking advantage of acidic oxidation treatment, GDY oxide (GDYO) with abundant surface oxygen-containing groups is obtained from pristine bulk GDY. Upon further thermal annealing of GDYO with H3BO3 under an inert atmosphere, B is introduced into GDY, while the loading of -C=O groups is increased onto B-GDY. We discover that boron-doped and ketonic carbonyl group-enriched graphdiyne as a dual-site carbon nanozyme endows it with an enhanced peroxidase-like activity, which is nearly 4.2-fold higher than that of GDY without B atoms and 6.6-fold higher than that of GDYO without B atoms and with low loading of -C=O groups. The high peroxidase-like activity of B-GDY is ascribed to the dual active sites (-C=O group and B atom) within it, which facilitates the adsorption and decomposition of H2O2 into hydroxyl radicals revealed by experimental and theoretical studies. Moreover, B-GDY is successfully employed to develop a colorimetric method for the detection of glucose with good sensitivity and selectivity. This work probes into the intrinsic peroxidase activity and structure-reactivity correlation, creating effective strategies for the preparation of GDY-based nanozymes.

Electrochemical Sensors Based on Metal-Porous Carbon Nanozymes for Dopamine, Uric Acid and Furazolidone

A series of electrochemical sensors based on metal-porous carbon nanozymes were developed for the detection of dopamine (DA), uric acid (UA) and furazolidone (FZ). The metal-porous carbon nanozymes were prepared by calcination of porous crystalline covalent-organic frameworks (COFs) loaded metal ions. By carbonizing, the COFs was transformed into carbon nanosheets (CN) and metal ions were reduced into 5–10 nm MNPs loaded on CN uniformly (CuNPs/CN, FeNPs/CN, NiNPs/CN and CoNPs/CN). These porous MNPs/CN nanozymes were used for electrochemical detection of DA, AA and FZ, showing good performance. The electrochemical sensor based on CuNPs/CN nanozymes was used to simultaneously measure DA and UA. The linear range of DA detection was 0.015 μ–140 μM, the linear range of UA detection was 0.03 μM–175 μM, and the sensitivity of DA and UA were 1.03 μA μM−1 cm−2 and 0.52 μA μM−1 cm−2. The sensitivity of sensors based on FeNPs/CN, CoNPs/CN and NiNPs/CN nanozymes to detect DA were 1.30 μA cm−2 μM−1, 1.07 μA cm−2 μM−1 and 0.88 μA cm−2 μM−1, the linear ranges were 35 nM–200 μM, 42 nM–250 μM and 52 nM–250 μM. The sensitivity of detecting UA were 0.310 μA cm−2 μM−1, 0.587 μA cm−2 μM−1 and 0.360 μA cm−2 μM−1, the linear ranges were 145 nM–900 μM, 77 nM–700 μM and 125 nM–800 μM. Finally, CuNPs/CN was also used to construct a FZ sensor with a linear range of 61.5 nM–200 μΜ and a detection limit of 20.1 nM. The sensors also have good reproducibility and repeatability.

MOF-derived N-doped porous carbon with active magnesium sites as an efficient oxidase mimic for biosensing

Transition metal-based N-doped carbon nanozymes have received great attentions recently, while rare study is on the main group metal-based ones. Here, we designed the N-doped porous carbon with active magnesium sites (Mg/NC) via carbonizing Mg-MOF precursor. The optimized Mg/NC-0.8 displayed a sheet structure. The doping of N and Mg reduced the diffusion and electron transfer resistance, accelerated electron transfer rate, and finally boosted the catalytic activity. The Mg/NC-0.8 showed superior oxidase-like activity capable of significantly promoting 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation. Relative to that of N-doped carbon (NC), the oxidase-like activity of the Mg/NC-0.8 increased by 10.94-fold. The mechanism study showed the generation of O2•−, 1O2 and •OH during Mg/NC-0.8 catalyzed TMB oxidation. The Mg/NC-0.8 displayed good affinity to TMB with a Km value of 0.169 mM. In terms of its high oxidase mimic activity, a sensitive and selective assay for detecting acetylcholinesterase (AChE) activity was set up via restraining TMB oxidation by thiocholine, which was from the AChE-induced hydrolysis of acetylthiocholine. The assay shows a linear concentration range of 0.0001 – 1 U L−1 AChE, with a detection limit of 1 × 10–4 U L−1. It was used to measure AChE activity in real samples.

Tantalum-carbon-integrated nanozymes as a nano-radiosensitizer for radiotherapy enhancement.

Radiotherapy (RT) plays a pivotal role in the comprehensive treatment of multiple malignant tumors, exerting its anti-tumor effects through direct induction of double-strand breaks (DSBs) or indirect induction of reactive oxygen species (ROS) production. However, RT resistance remains a therapeutic obstacle that leads to cancer recurrence and treatment failure. In this study, we synthesised a tantalum-carbon-integrated nanozyme with excellent catalase-like (CAT-like) activity and radiosensitivity by immobilising an ultrasmall tantalum nanozyme into a metal-organic framework (MOF)-derived carbon nanozyme through in situ reduction. The integrated tantalum nanozyme significantly increased the CAT activity of the carbon nanozyme, which promoted the production of more oxygen and increased the ROS levels. By improving hypoxia and increasing the level of ROS, more DNA DSBs occur at the cellular level, which, in turn, improves the sensitivity of RT. Moreover, tantalum-carbon-integrated nanozymes combined with RT have demonstrated notable anti-tumor activity in vivo. Therefore, exploiting the enzymatic activity and the effect of ROS amplification of this nanozyme has the potential to overcome resistance to RT, which may offer new horizons for nanozyme-based remedies for biomedical applications.

Dual-mode colorimetric and fluorescence sensing system for the detection of captopril based on Fe/NC nanozymes and carbon dots

Metal nitrogen-doped carbon (MNC) nanozymes have received increasing attention in bio-catalysis filed due to adequate catalytic activity, outstanding stability and reusability. Herein, the Fe/NC nanozymes (Fe/NC NZs) with peroxidase-like activity was successfully synthesized and a fluorescence turn on and colorimetric dual-mode sensing system was developed for quantification of captopril (CP) based on Fe/NC NZs and orange-emitting carbon dots (O-CDs). The Fe/NC NZs as an enzyme mimic can efficiently catalyze the 3,3′,5,5′-tetramethylbenzidine (TMB) chromogenic reaction, forming blue-colored oxidized TMB product (oxTMB) with the presence of H2O2, leading to the fluorescence quenching of O-CDs simultaneously via the inner filter effect (IFE). When CP was present, the blue oxTMB was reduced to colorless TMB, resulting in the inhibition of IFE and the recovery of fluorescence of O-CDs. The fluorescence increase of O-CDs and absorbance decrease of oxTMB depended on CP concentration. Good linear relationships of fluorescence and colorimetric sensing towards CP were obtained in the range from 1 to 50 μM, and the detection limits were 0.47 and 0.56 μM, respectively. Moreover, this as-constructed dual-mode sensor was used to detect CP in pharmaceutical products with satisfactory results.