Enzyme-mimicking capacities of carbon-dots nanozymes: Properties, catalytic mechanism, and applications - A review

Multifunctional nanozymatic biosensors: Awareness, regulation and pathogenic bacteria detection

It is estimated that approximately 700,000 fatalities occur annually due to infections attributed to various pathogens, which are capable of dissemination via multiple environmental vectors, including air, water, and soil. Consequently, there is an urgent need to enhance and refine rapid detection technologies for pathogens to prevent and control the spread of associated diseases. This review focuses on applying nanozymes in constructing biosensors, particularly their advancement in detecting pathogenic bacteria. Nanozymes, which are nanomaterials exhibiting enzyme-like activity, combine unique magnetic, optical, and electronic properties with structural diversity. This blend of characteristics makes them highly appealing for use in biocatalytic applications. Moreover, their nanoscale dimensions facilitate effective contact with pathogenic bacteria, leading to efficient detection and antibacterial effects. This article briefly summarizes the development, classification, and strategies for regulating the catalytic activity of nanozymes. It primarily focuses on recent advancements in constructing biosensors that utilize nanozymes as probes for sensitively detecting pathogenic bacteria. The discussion covers the development of various optical and electrochemical biosensors, including colorimetric, fluorescence, surface-enhanced Raman scattering (SERS), and electrochemical methods. These approaches provide a reliable solution for the sensitive detection of pathogenic bacteria. Finally, the challenges and future development directions of nanozymes in pathogen detection are discussed.

Dual-mode sensors based on double enzyme-mimicking MnCu nanoflowers as fluorescence probe for the detection of organophosphorus pesticides and 2,4-dichlorophenol

Organophosphorus pesticides (OPs) and 2,4-dichlorophenol (2,4-DP) are widely used, but their residues have brought serious threatens to environment and human health as environmental pollutants. We synthesized double enzyme-mimicking and multifunctional MnCu flower-like nanoenzymes (NH2-MnCu NFs) with fluorescence properties, oxidase (OXD)-like activity and laccase-like activity. NH2-MnCu NFs exhibit excitation-independent emission fluorescence properties, as well as excellent OXD-like activity (Km = 0.230 mM, Vmax = 2.46 × 10-6 M/s) and laccase-like activity (Km = 0.186 mM, Vmax = 3.46 × 10-2 mM/min). The mechanism of 2,3-diaminophenazine (DAP)-induced quenching of the fluorescence of NH2-MnCu NFs was thoroughly investigated, revealing that it results from the combined effects of the internal filtering effect (IFE), dynamic quenching effect (DQE), and static quenching effect (SQE). It was found that -SH could disrupt the OXD-like activity of NH2-MnCu NFs according to morphological and structural perspectives using SEM and in situ Raman spectroscopy. Based on OXD-like activity, ratiometric fluorescence and colorimetric dual-mode sensor was constructed for the detection of OPs. Additionally a colorimetric fluorescence dual-mode sensor was proposed for the specific detection of 2,4-DP with the use of laccase-like activity of the material. Two sensors were constructed using a single type of nanoenzyme, leveraging their dual-enzyme activities for the detection of OPs and 2,4-DP, respectively. This approach expands the potential applications of nanoenzymes and provides versatile scenarios for their multifunctional use.

Metal-organic framework-based nanozymes for water-soluble antioxidants and Total antioxidant capacity detection: Principles and applications

Nanozymes, engineered catalysts exhibiting catalytic properties, have emerged as key players at the interface of nanotechnology and biology, holding great promise in diverse food applications. Notably, nanoscale metal-organic frameworks (MOFs) have gained widespread recognition as flexible platforms for developing potent nanozymes. This review explores the design, development, and applications of MOF-based nanozymes, with a focus on their potential in detecting antioxidants and total antioxidant capacity (TAC), two critical parameters in the assessment of oxidative stress and related diseases. A comprehensive classification of these MOF-based nanozymes is presented, based on their catalytic activities, and recent advancements in their application to antioxidants and TAC detection are discussed. The review further delves into the challenges faced by MOF nanozymes in these areas, including issues related to stability, reproducibility, and selectivity. By addressing these challenges and proposing potential solutions, the review offers future perspectives on advancing the use of MOF nanozymes in sensing applications.

Flower-like Ag-ZIF nanoparticles with petal-like structures as effective hot/cold-adapted oxidase mimic: Visual color tonality nitrite detection

This study presents the synthesis of novel flower-like silver-based zeolitic imidazolate frameworks (Ag-ZIFs) with petal-like nanosheet structures, exhibiting robust oxidase-like activity. These nanozymes catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) effectively across a wide temperature range (5 °C to 80 °C), making them suitable for thermophilic and cryogenic applications. Leveraging this strong oxidase activity, Ag-ZIFs@TMB system was used to design a conventional ratiometric colorimetric method for nitrite detection in water and food samples, alongside a color tonality-based visual detection mode. Nitrite concentrations ranging from 1.0 to 54.0 μM were quantified, achieving a detection limit of 0.06 μM. The ratiometric approach demonstrated enhanced sensitivity, lower detection limits, and superior resistance to interference compared to traditional single-absorbance methods. Furthermore, the smartphone-assisted or naked-eye detection mode enabled rapid, portable, and accurate analysis, offering practical applications in environmental monitoring and food safety. These results highlight the multifunctional potential of Ag-ZIFs in advanced sensing technologies.

Single-well colorimetric sensor array for discrimination and smartphone-assisted detection of catecholamines based on Fe-carbon dots nanozymes

BACKGROUND

Catecholamines (CAs), such as noradrenaline (NE), adrenaline (AD), and dopamine (DA), are essential signaling mediators that regulate various physiological functions. Monitoring their levels is crucial for studying and diagnosing diseases, as abnormal concentrations are associated with numerous health conditions. However, distinguishing between these CAs is challenging due to their highly similar molecular structures.

RESULTS

In this study, Fe-doped carbon dot-based nanozymes (Fe-CDs) with strong peroxidase-like activity were synthesized using a simple one-pot method. Fe-CDs-based sensing systems exhibit excellent stability, reproducibility, sensitivity (with detection limits of 26.6 nM for NE, 46.0 nM for AD, and 33.3 nM for DA), and anti-interference properties. A triple-channel single-well colorimetric sensor array was developed by collecting the absorbance at 20, 40, and 60 min as sensing units, enabling the effective differentiation and identification of various CAs.

SIGNIFICANCE

The Fe-CDs-based system has proven capable of detecting CAs in real human urine and fetal bovine serum. Additionally, the Fe-CDs-based smartphone-assisted platform provides efficient, highly sensitive, and on-site CAs detection, making it highly promising for biomedical and diagnostic applications.

Biomass spinach-drived metal-free carbon dots-based nanozyme for multimodal nitrite sensing and functionalized by glucose oxidase as ROS amplifiers to enhance tumor therapy

The metal-free carbon dots (CDs) nanozyme, which is endowed generation of multiple reactive oxygen species (ROS), followed by highly selective chemical sensing, remains a critical challenge. The exceptional biocatalytic properties of glucose oxidase (GOx) have spurred the development of GOx-functionalized nanocatalysts for cancer therapy. Here, the innovative free metal-doped CDs and CDs@GOx nanozymes with peroxidase (POD)-like activity were developed, which specifically catalyzed H₂O₂ to engender multiple ROS including •O2-, 1O2 and •OH, to oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB, indicating both nanozymes can be as ROS amplifiers to enhance tumor therapy. The introduction of NO₂- triggered a distinct color change from blue to green ascribed to the diazotization of ox-TMB along with quenching the fluorescence of CDs, which endowed high selectivity and sensitivity for NO2- detection. Furthermore, CDs catalyzed endogenous H₂O₂ within tumor cells, to effectively destroy cancer cells rather than normal cells. As expected, CDs@GOx preferentially catalyze glucose in cancer cells to further supply H2O2, allowing more ROS accumulation, thereby realizing the integration of starvation therapy and ROS therapy of cancer. Notably, in vivo anti-tumor efficacy demonstrated that CDs and CDs@GOx markedly inhibited tumor growth without external stimulation with neglected side effects. Compared to the saline group, the tumor size was reduced by 3 or 4 times for CDs and CDs@GOx, respectively. This metal-free CDs tailors a convenient and impactful nanoplatform for chemical sensing and as ROS amplifiers to enhance tumor therapy by non-invasive treatment.

Carbon dot superoxide dismutase nanozyme enhances reactive oxygen species scavenging in diabetic skin wound repair

INTRODUCTION

The accumulation of reactive oxygen species (ROS) in diabetic wounds leads to inflammation and impaired neovascularization. Recent studies have indicated that carbon dot nanozymes (C-dots) exhibiting superoxide dismutase (SOD)-like activity can neutralize excessive ROS and mitigate diseases associated with oxidative stress.

OBJECTIVES

Our study was designed to evaluate the therapeutic impact of C-dots on the healing of diabetic wounds and to unravel the complex molecular mechanisms through which these nanozymes modulate oxidative stress and inflammatory responses within the wound microenvironment.

METHODS AND RESULTS

We synthesized C-dots from carbon fiber and confirmed their structure using transmission electron microscopy. The presence of carbon-carbon double bonds on the C-dots was verified with X-ray photoelectron spectroscopy. We assessed the scavenging capacity of C-dots for superoxide anion, hydroxyl radical, and nitric oxide radical using electron spin resonance spectroscopy. Their SOD-like activity and total antioxidant capacity were evaluated with commercial assay kits. In vitro experiments showed that C-dots effectively scavenged excessive ROS, protecting human keratinocytes, vascular endothelial cells, and fibroblasts from oxidative stress-induced damage. Concurrently, C-dots increased the migratory capacity of fibroblasts. In a streptozocin-induced diabetic mice model, C-dots application enhanced skin wound healing, evidenced by accelerated re-epithelialization and orderly collagen matrix assembly. Mechanistic investigations indicated that C-dots markedly suppressed ROS generation and diminished the levels of inflammatory cytokines in the wound environment. Additionally, C-dots induced an M2 polarization phenotype in macrophages and promoted neovascularization, indicating a transition from the inflammatory to the proliferative phase. Quantitative proteomic analysis was conducted to further clarify the underlying mechanisms of C-dots in ameliorating diabetic wounds.

CONCLUSION

C-dots represent a robust nanomaterial-based strategy for treating diabetic wounds, with the ability to accelerate healing by alleviating oxidative stress, mitigating harmful inflammatory responses, and fostering angiogenesis. This highlights their significant therapeutic potential in the field of biomedicine.

Progress in the Computer-Aided Analysis in Multiple Aspects of Nanocatalysis Research

Making the utmost of the differences and advantages of multiple disciplines, interdisciplinary integration breaks the science boundaries and accelerates the progress in mutual quests. As an organic connection of material science, enzymology, and biomedicine, nanozyme-related research is further supported by computer technology, which injects in new vitality, and contributes to in-depth understanding, unprecedented insights, and broadened application possibilities. Utilizing computer-aided first-principles method, high-speed and high-throughput mathematic, physic, and chemic models are introduced to perform atomic-level kinetic analysis for nanocatalytic reaction process, and theoretically illustrate the underlying nanozymetic mechanism and structure-function relationship. On this basis, nanozymes with desirable properties can be designed and demand-oriented synthesized without repeated trial-and-error experiments. Besides that, computational analysis and device also play an indispensable role in nanozyme-based detecting methods to realize automatic readouts with improved accuracy and reproducibility. Here, this work focuses on the crossing of nanocatalysis research and computational technology, to inspire the research in computer-aided analysis in nanozyme field to a greater extent.

Fabrication of a novel reusable nanozyme by immobilizing Co-doped carbon dots on nanocellulose aerogels for efficient dyes degradation

Carbon dot-based nanozymes have gained significant attention, but their application in dye degradation remains limited due to low activity and challenges in recovery and reuse. To overcome these limitations, high peroxidase-active Co-doped carbon dots (CoCDs) with surface amines were synthesized via hydrothermal method and immobilized onto TEMPO-oxidized cellulose nanofibrils (TOCNF) aerogels using EDC/NHS coupling. For the first time, this study investigates the dye degradation efficiency of CDs nanozyme. CoCDs with 1.456 % Co content exhibited excellent peroxidase-like activity with favorable kinetics (Km = 1.746 mM, Vmax = 22.05 × 10-8 Ms-1 for TMB and Km = 1.542 mM, Vmax = 23.54 × 10-8 Ms-1 for H2O2). The immobilized CoCDs enhanced the structural stability, and shape recovery of aerogels, even after multiple compressions. CoCDs/TOCNF aerogel with maximum CoCDs (114.7 mg/g) exhibited superior degradation efficiency for various dyes, including methyl orange (MO), methylene blue (MB), and rhodamine B (RhB), with rate constants of 12.7 × 10-3, 17.4 × 10-3, and 12.2 × 10-3 min-1, respectively. Mechanistic studies revealed the major role of hydroxyl radicals in dye degradation. The aerogels exhibited exceptional recyclability with all dyes. This stable and recyclable nanozyme with high catalytic activity presents a promising avenue for environmental remediation.

Carbon-based nanozymes for cancer therapy and diagnosis: A review

Carbon-based nanozymes (CNs) have emerged as a significant innovation in targeted cancer therapy, demonstrating great potential for advancing cancer diagnosis and treatment. With exceptional catalytic properties, remarkable biocompatibility, and the ability to precisely target cancer cells, CNs provide a promising avenue for the development of novel oncological therapies. By functionalizing their surfaces with targeting ligands, such as antibodies or peptides, CNs can specifically recognize and bind to cancer cells. This targeted approach ensures that therapeutic agents are delivered directly to the tumor site, minimizing off-target effects, and reducing systemic toxicity. Additionally, the enzyme-like activities of CNs, when combined with conventional therapies such as chemotherapeutics, photothermal therapy, and photodynamic therapy, or other modalities can enhance therapeutic outcomes. Integrating CNs into clinical practice could significantly improve therapeutic efficacy, reduce probable side effects, enhance patient outcomes, and drive a shift towards more personalized cancer care. Besides, CNs can also be employed in biosensors and diagnostic nanomaterials, enabling rapid, selective, and highly accurate detection of specific biomarkers. Their versatile functionalities open new avenues for refining imaging techniques, ultimately contributing to early diagnosis and better clinical decision-making. This review consolidates recent studies exploring CNs in cancer targeting, highlighting both their diagnostic and therapeutic potential in oncology.

Revolutionizing nanozymes: The synthesis, enzyme-mimicking capabilities of carbon dots, and advancements in catalytic mechanisms

Nanozymes, a revolutionary category of engineered artificial enzymes based on nanomaterials, have been developed to overcome the inherent limitations of natural enzymes, such as the high cost associated with storage and their fragility. Carbon dots (CDs) have emerged as compelling candidates for various applications due to their versatile properties. Particularly noteworthy are CDs with a range of surface functional groups that exhibit enzyme-like behavior, combining exceptional performance with catalytic capabilities. This review explores the methodologies used for synthesizing CDs with enzyme mimicking capabilities, highlighting potential avenues such as doping and hybrid nanozymes to enhance their catalytic efficacy. Moreover, a comprehensive overview of CDs that mimick the activities of various oxidoreductases-like peroxidase, catalase, oxidase/laccase, and superoxide dismutase-like is provided. The focus is on the in-depth exploration of the mechanisms, advancements and practical applications of each oxidoreductase-like function exhibited by CD nanozymes. Drawing upon these exhaustive summaries and analyses, the review identifies the prevailing challenges that hinder the seamless integration of CDs into real-world applications and offers forward-looking perspectives for future directions.

Nanotherapies Based on ROS Regulation in Oral Diseases

Oral diseases rank among the most prevalent clinical conditions globally, typically involving detrimental factors such as infection, inflammation, and injury in their occurrence, development, and outcomes. The concentration of reactive oxygen species (ROS) within cells has been demonstrated as a pivotal player in modulating these intricate pathological processes, exerting significant roles in restoring oral functionality and maintaining tissue structural integrity. Due to their enzyme-like catalytic properties, unique composition, and intelligent design, ROS-based nanomaterials have garnered considerable attention in oral nanomedicine. Such nanomaterials have the capacity to influence the spatiotemporal dynamics of ROS within biological systems, guiding the evolution of intra-ROS to facilitate therapeutic interventions. This paper reviews the latest advancements in the design, functional customization, and oral medical applications of ROS-based nanomaterials. Through the analysis of the components and designs of various novel nanozymes and ROS-based nanoplatforms responsive to different stimuli dimensions, it elaborates on their impacts on the dynamic behavior of intra-ROS and their potential regulatory mechanisms within the body. Furthermore, it discusses the prospects and strategies of nanotherapies based on ROS scavenging and generation in oral diseases, offering alternative insights for the design and development of nanomaterials for treating ROS-related conditions.

Designing Artificial Laccase Catalysts by Introducing Substrate Oxidation Metals into Oxygen-Reducing Metal-Organic Frameworks: Cu-Doped ZIF-67

Laccase, a multi-copper oxidase, is limited by its optimal temperature range and isolation costs. To overcome these challenges, we synthesized copper-doped zeolitic imidazolate framework-67 (Cu-doped ZIF-67) with 16 mol % Cu as an artificial laccase catalyst. The introduced Cu site acts as the phenol oxidation site, and Co-based ZIF-67 is the four-electron oxygen reduction site. Laccase also employs this division of oxidation and reduction sites. Cu-doped ZIF-67 demonstrated significant catalytic activity, superior to natural laccase, especially at elevated temperatures, and maintained stability across multiple reaction cycles. These findings suggest that Cu-doped ZIF-67 is a robust, reusable alternative for industrial applications requiring high thermal stability and efficient catalysis.

Carbon dots encapsulated zeolitic imidazolate framework-8 as an enhanced multi-antioxidant for efficient cytoprotection to HK-2 cells

Excessive reactive oxygen species (ROS) can lead to the imbalance of antioxidant system in the body and cause oxidative damage to cells. It is imperative to rationally design nanomaterials with high catalytic activity and multiple antioxidant activities. Here, line peppers-derived carbon dots (CDs) is encapsulated into zeolitic imidazolate framework-8 (CDs@ZIF-8) to achieve enhanced antioxidant activities for improved protective effect on cells. This nanosystem has a broad spectrum of antioxidant properties, which can effectively remove a variety of intracellular ROS and protect cells from ROS-induced death and cytoskeleton damage. In addition, CDs@ZIF-8 can reduce malondialdehyde (MDA) level and increase the enzyme activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx), as well as the level of glutathione (GSH) in human kidney proximal tubular epithelial cells (HK-2) cells. Mechanism studies demonstrated that CDs@ZIF-8 can up-regulate the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), allowing the regulation of antioxidant enzymes to further achieve antioxidant effect. Besides, CDs@ZIF-8 inhibited the secretion of proinflammatory cytokines. This work demonstrates that the constructed CDs@ZIF-8 with multi-antioxidant activity can act as a highly efficient intracellular ROS scavenger and provide potential for the application in related oxidative stress-induced diseases.

Rational design of carbon dot nanozymes for ratiometric dual-signal and smartphone-assisted visual detection of nitrite in food matrices

Developing reliable nitrite (NO2-) sensors is essential for food safety and reducing health risks from NO2- exposure. In this study, we strategically designed nitrogen-doped carbon dot (N-CD) nanozymes to establish an accessible dual-signal ratiometric sensing system for detecting NO2- in food matrices. This system utilizes the photoluminescence and enzyme-like properties of N-CD nanozymes combined with NO2--triggered diazotization reactions of substrates such as o-phenylenediamine (OPD) or 3,3',5,5'-tetramethylbenzidine (TMB). The resulting N-CD/OPD and N-CD/TMB composites provide dual-mode detection-fluorescence and colorimetric-with high selectivity for NO2- and excellent resistance to interference. These sensors exhibit clear color changes under both ultraviolet and visible light, and can be combined with smartphones for visual, on-site detection of NO2-. By incorporating a ratiometric strategy, dual-signal output, and smartphone compatibility, our system achieved a low detection limit (≤ 1.92 μM) and satisfactory recovery rates (85.6-115 %) in environmental water and food samples. This highlights the potential of smartphone-assisted sensors for environmental monitoring and food safety applications. Our carbon dot-based platform offers a practical and effective solution for on-site NO2- detection, contributing valuable insights to the field.

Colorimetric-SERS dual-mode aptasensor for Staphylococcus aureus based on MnO2@AuNPs oxidase-like activity

The nanozyme-linked aptamer-sorbent assay (NLASA) is a rapid way to screen and characterize aptamer binding to targets. In this paper, a MnO2@AuNPs@aptamer (Apt) based NLASA coupled with colorimetric-SERS dual-mode for Staphylococcus aureus (S. aureus) detection is presented. Cu,Fe-CDs were used as the reducing agent to synthesize MnO2 and gold nanoparticles (AuNPs). Then, they were fabricated to obtain MnO2@AuNPs with oxidase (OXD)-like and SERS activities. The S. aureus aptamer was conjugated to MnO2@AuNPs and enhanced the OXD-like activity, which realized the specific capture of S. aureus in food matrices. In addition, S. aureus improves the oxidation of 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid (ABTS) but inhibits 3,3',5,5'-tetramethylbenzidine (TMB) to generate Raman-active oxTMB with MnO2@AuNPs@Apt. This sensor was used for detections of S. aureus in a concentration ranged from 101 to 107 CFU/mL with a detection limit of 0.926 CFU/mL (colorimetric) and 1.561 CFU/mL (SERS), and the recovery is 85%-105% in real samples.

A molecularly imprinted electrochemiluminescence sensor based on mimic enzyme ZIF-90 and MnO2/g-C3N4 magnetic particles for detection of methidathion

Methidathion (MTDT), a common organophosphorus pesticide with high insecticidal activity, is widely used for pest control. However, the misuse of MTDT leads to widespread residues and endangers human health. Therefore, it is crucial to develop a simple and highly sensitive method for the detection of MTDT residues. Herein, ZIF-90/MnO2/g-C3N4/Fe3O4 composite particles were synthesized: The  MnO2 nanosheets could absorb the energy of the excited g-C3N4 to quench the ECL of g-C3N4 while ZIF-90 acted as a mimetic enzyme to catalyze the formation of thiocholine from MTDT. The thiocholine caused the reduction of MnO2 to Mn2+, restoring the ECL signal of g-C3N4. Combined with molecular imprinting technique, an electrochemiluminescence sensor was constructed for the determination of MTDT. The determination range was 1.00 × 10-9 ~ 7.00 × 10-7 g/L, and the detection limit was 6.58 × 10-10 g/L. Structurally similar organophosphorus pesticides showed no cross-reactivity. The method has high sensitivity and specificity, and has been successfully applied to the determination of MTDT residue in fruits with recoveries in the range 93.75% ~ 102.37%.

Preparation of Fe,Co,P-Codoping Peroxidase-like Green-Emitting Carbon Dots and Its Application in Monitoring the Freshness of Aquatic Products

Carbon dot (CD) nanozymes with excellent fluorescence properties and mimetic enzyme activity have exhibited great potential in monitoring the freshness of meat products. This paper reports the synthesis of Fe, Co, and P codoped CD nanozymes (quantum yields = 48.76%) through a one-step hydrothermal route. The product showed green fluorescence and peroxidase (POD) activity. Because the fluorescence intensity and emission wavelength of prepared CDs change with pH, a pH sensor has been developed to monitor the pH change caused by volatile biogenic amines during the spoilage process of aquatic products. Moreover, this CD biosensor has been used to realize the sensitive and visual detection of hypoxanthine (Hx, the marker of the spoilage of aquatic products) based on the inhibitory effect of Hx upon the POD activity of CDs. This study provides a new strategy for preparing high-quality CD nanozymes and its application in low-cost and visual monitoring of the freshness of aquatic products.

Fluorescent Iron-Doped Polymer Dot Nanozyme-Based Cascade System for Dual-Mode Detection of Acetylcholinesterase Activity and Its Inhibitors

The advancement of acetylcholinesterase (AChE) activity and its inhibitor assays is crucial for clinical diagnosis, drug screening, and environmental monitoring. A nanozyme-mediated cascade reaction system could offer promising prospects for a wide range of applications in such biosensing; however, the creation of nanozyme catalysts with diverse functionalities remains a significant challenge. Herein, we have proposed a multifunctional iron-doped polymer dots (Fe-PDs) nanozyme possessing excellent fluorescence and peroxidase (POD)-mimicking activity. Notably, the Fe-PDs nanozyme is capable of catalyzing H2O2 to produce a series of reactive oxygen species, which can simultaneously quench the fluorescence of Fe-PDs and induce a chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB), enabling the dual-mode detection of H2O2 through both fluorescence turn-off and absorbance turn-on signals. Furthermore, by integrating acetylcholine (ACh) and choline oxidase (ChOx), we have developed a three-enzyme (AChE-ChOx-POD) cascade-based fluorometric and colorimetric dual-mode sensing platform for monitoring AChE activity and its inhibitors. The sensitive and convenient dual-mode sensor has achieved low limits of detection with 0.5 mU/mL (fluorometry) and 0.014 mU/mL (colorimetry) for AChE, respectively, which are superior to the traditional Ellman's assay. More significantly, this sensor can also be extended to detect the reversible and irreversible inhibitors of AChE, such as tacrine (IC50 = 23.3 nM) and carbaryl (LOD = 0.8 nM). We firmly believe that this innovative dual-mode nanozyme-involved multienzyme cascade system-based sensing strategy will stimulate further exploration and serve as a versatile and practical tool for biochemical sensing applications.

The Exploration of Nanozymes for Biosensing of Pathological States Tailored to Clinical Theranostics

The nanozymes (NZs) are the artificial catalyst deployed for biosensing with their uniqueness (high robustness, surface tenability, inexpensive, and stability) for obtaining a better response/miniaturization of the varied sensors than their traditional ancestors. Nowadays, nanomaterials with their broadened scale such as metal-organic frameworks (MOFs), and metals/metal oxides are widely engaged in generating NZ-based biosensors (BS). Diverse strategies like fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and electrochemical sensing principles were implemented for signal transduction of NZs. Despite broad advantages, numerous encounters (like specificity, feasibility, stability, and issues in scale-up) are affecting the potentialities of NZs-based BS, and thus need prior attention for a promising exploration for a revolutionary outcome in advanced theranostics. This review includes different types of NZs, and the progress of numerous NZs tailored bio-sensing techniques in detecting abundant bio analytes for theranostic purposes. Further, the discussion highlighted some recent challenges along with their progressive way of possibly overcoming followed by commercial outbreaks.

Antioxidant Carbon Dots Nanozymes Alleviate Stress-induced Depression by Modulating Gut Microbiota

Depression is a debilitating mental illness that severely threatens millions of individuals and public health. Because of the multifactorial etiologies, there is currently no cure for depression; thus, it is urgently imperative to find alternative antidepressants and strategies. Growing evidence underscores the prominent role of oxidative stress as key pathological hallmarks of depression, making oxidative stress a potential therapeutic target. In this study, we report a N-doped carbon dot nanozyme (CDzyme) with excellent antioxidant capacity for treating depression by remodeling redox homeostasis and gut microbiota. The CDzymes prepared via microwave-assisted fast polymerization of histidine and glucose exhibit superior biocompatibility. Benefiting from the unique structure, CDzymes can provide abundant electrons, hydrogen atoms, and protons for reducing reactions, as well as catalytic sites to mimic redox enzymes. These mechanisms collaborating endow CDzymes with broad-spectrum antioxidant capacity to scavenge reactive oxygen and nitrogen species (•OH, O2-•, H2O2, ONOO-), and oxygen/nitrogen centered free radicals. A depression animal model was established by chronic unpredictable mild stress (CUMS) to evaluate the therapeutic efficacy of CDzymes from the behavioral, physiological, and biochemical index and intestinal flora assessments. CDzymes can remarkably improve depression-like behaviors and key neurotransmitters produced in hippocampus tissues and restore the gut microbiota compositions and the amino acid metabolic functions, proving the potential in treating depression through the intestinal-brain axis system. This study will facilitate the development of intestinal flora dysbiosis nanomedicines and treatment strategies for depression and other oxidative stress related multifactorial diseases.

Self-assembling gelatin based delivery of multienzyme activity nanozyme and photosensitizer for ROS storm based cancer therapy

Nanozymes with multienzyme activity for reactive oxygen species (ROS) generation and intracellular redox imbalance are attractive strategy for cancer therapy. However, it is severely limited by low biocompatibility and catalytic efficiency, hypoxic and high levels of GSH in the tumor microenvironment. To address these issues, a copper doping carbon nanozyme (CC) with multienzyme activity was designed and integrated with photosensitizer Ce6 and gelatin to fabricate ROS amplifier (CCC). Gelatin endowed CCC with good biocompatibility, low hemolysis, and enzyme responsive degradation. CCC with high CAT-like, POD-like, OXD-like, and GSHox-like activities can induce the intracellular ROS storm formation to eliminate the cancer cells. The OXD-like activity and PDT performance mediated 1O2 generation was markedly potentiated by the CAT-like activity of CCC via catalyzing high expression of H2O2 to generate O2. At the same time, a large amount of ·OH were produced through POD-like activity of CCC and GSH was depleted by the GSHox-like activities of CCC, resulting in a destructive ROS storm formation and cellular redox homeostasis disruption. Both in vivo and in vitro experiments showed that CCC displayed satisfactory anti-tumor activity and biocompatibility. Our work provides a novel strategy for the development of nanozyne enhanced photodynamic therapy of cancer.

Aptamer-functionalized Fe3O4/MWCNTs@Mo-CDs nanozyme for rapid colorimetric detection toward Escherichia coli

The pathogenic bacteria induced foodborne disease has been detrimental to public health worldwide. Herein, the peroxidase (POD)-like Fe3O4/MWCNTs@Mo-CDs (FMMC) nanozyme was applied for the detection of Escherichia coli (E. coli). The E. coli aptamer was conjugated with the surface of the FMMC, which effectively enhanced the POD-like activity attributing to the higher affinity to the substrate, and then specific capture of E. coli in food matrices, leading to the reduction of POD-like activity. Therefore, a robust and facile colorimetric aptasensor was developed for detecting E. coli with a wide linear range of 101-106 CFU/mL, low LOQ of 101 CFU/mL and LOD of 0.978 CFU/mL. The aptasensor demonstrated the satisfied selectivity for E. coli compared to the other strains. This method possessed the potential application for fast in situ screening of foodborne pathogens in food products.

Ultra-trace Ag doped carbon quantum dots with peroxidase-like activity for the colorimetric detection of glucose

Carbon quantum dots (CQDs) have significant applications in nanozymes. However, previous studies have not elucidated the structure-activity relationship and enzyme mechanism. In this study, we employed a one-step microwave method to synthesize ultra-trace Ag-doped carbon quantum dots (Ag-CQDs). In the presence of hydrogen peroxide (H2O2), we used the oxidative coupling reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to evaluate the intrinsic peroxidase-like activity, kinetics, and mechanism of Ag-CQDs. The trace amount of doped Ag (1.64 %) facilitated electron transfer from the CQDs interior to the surface. The electron transfer triggered the peroxide activity of CQDs, producing hydroxyl radical (·OH), which oxidized the colorless TMB to blue-colored TMB (oxTMB). By coupling with glucose oxidase (GOx), the Ag-CQDs/H2O2/TMB system has been used for colorimetric glucose determination. The system demonstrated a low detection limit (0.17 µM), wide linear range (0.5-5.5 µM), and satisfactory results when fruit juice was analyzed. This study reports a feasible method for the colorimetric detection of glucose by synthesizing ultra-trace Ag-doped carbon quantum dots with peroxidase-mimicking activity.

Effect of carbon dots supplementation in Chlorella vulgaris biomass production and its composition

Microalgae cultures have an excellent ability to capture CO2 and produce high, medium, and low valuable biocompounds such as proteins, carbohydrates, lipids, pigments, and polyhydroxyalkanoates; those compounds have shown excellent properties in the pharmaceutical, cosmetic, food, and medical industries. Recently, the supplementation of carbon dots (CDs) in autotrophic microalgae cultures has been explored as a new strategy to increase light capture and improve photoluminescence, which in turn enhances biomass growth and biocompounds production. In this work, we synthesized CDs through a simple carbonization method using orange juice as a natural precursor. The green synthesized CDs were analyzed in detail through characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), UV–visible, fluorescence spectroscopy, and ζ potential analysis. Moreover, CDs were added to Chlorella vulgaris to analyze the response under different photoperiod cycles and CDs dosages. The optimal results were obtained with the addition of 0.5 mg l−1 of CDs under a photoperiod cycle of 16 h:8 h (light:dark). In these conditions, a maximum biomass production of 2.12 g l−1 was observed, which represents an enhancement of 112% and 17% in comparison to the control samples under the photoperiod of 12 h:12 h and 16 h:8 h (light/dark), respectively. Furthermore, the production of lipids, proteins, and carbohydrates was significantly increased to 249 mg g−1, 285 mg g−1, and 217 mg g−1 dry weight, respectively. These results suggest that the addition of CDs enhances cell growth and increases the production of lipids and proteins, being a strategy with great potential for the food and pharmaceutical industries.

Integrating of analytical techniques with enzyme-mimicking nanomaterials for the fabrication of microfluidic systems for biomedical analysis

Bioanalysis faces challenges in achieving fast, reliable, and point-of-care (POC) determination methods for timely diagnosis and prognosis of diseases. POC devices often display lower sensitivity compared to laboratory-based methods, limiting their ability to quantify low concentrations of target analytes. To enhance sensitivity, the synthesis of new materials and improvement of the efficiency of the analytical strategies are necessary. Enzyme-mimicking materials have revolutionized the field of the fabrication of new high-throughput sensing devices. The integration of microfluidic chips with analytical techniques offers several benefits, such as easy miniaturization, need for low biological sample volume, etc., while also enhancing the sensitivity of the probe. The use enzyme-like nanomaterials in microfluidic systems can offer portable strategies for real-time and reliable detection of biological agents. Colorimetry and electrochemical methods are commonly utilized in the fabrication of nanozyme-based microfluidic systems. The review summarizes recent developments in enzyme-mimicking materials-integrated microfluidic analytical methods in biomedical analysis and discusses the current challenges, advantages, and potential future directions.

A portable fluorescence detection device based on a smartphone employing carbon nanodots for Mn2+ sensing

The measurement of fluorescence emission for quantitative analysis is typically based on a traditional spectrofluorometer, which limits an onsite detection approach. Thus, an alternative device should be developed for fulfilling this analysis outside of the laboratory. Therefore, a low-cost, portable, and low-energy consumption fluorescence reader-based smartphone device was developed. An ultraviolet light-emitting diodes (UV-LED) was used to construct the fluorescence device-based smartphone as a low-power excitation light source. The smartphone camera was used as a detector for detecting photons from the fluorescence emission process of the fluorescence probe and was connected to a digital image platform. Transparent acrylic with orange and yellow colors was employed as a filter for reducing the interference from light source intensity. The obtained digital image was converted to red, green and blue (RGB) intensity using a custom-designed smartphone application. N,S-doped carbon nanodots (N,S-CDs) were demonstrated to be a good fluorescence indicator for determining trace quantities of Mn2+ in cosmetics. The approach exhibited high selectivity and sensitivity, detecting and quantifying analytes at 1-5 μM concentrations. Furthermore, the method's detection limit of 0.5 μM reflects its capacity to detect trace amounts of a target analyte. Mn2+ in cosmetic products was successfully analyzed using this device with high accuracy comparable with the results from inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Ce6-modified Fe ions-doped carbon dots as multifunctional nanoplatform for ferroptosis and photodynamic synergistic therapy of melanoma

BACKGROUND

Despite the higher sensitivity of melanoma towards ferroptosis and photodynamic therapy (PDT), the lack of efficient ferroptosis inducers and the poor solubility of photosensitizers restrict their synergistic strategies. With unique advantages, carbon dots (CDs) are expected to serve as innovative building blocks for combination therapy of cancers.

RESULTS

Herein, an ferroptosis/PDT integrated nanoplatform for melanoma therapy is constructed based on chlorin e6-modified Fe ions-doped carbon dots (Fe-CDs@Ce6). As a novel type of iron-carbon hybrid nanoparticles, the as-prepared Fe-CDs can selectively activate ferroptosis, prevent angiogenesis and inhibit the migration of mouse skin melanoma cells (B16), but have no toxicity to normal cells. The nano-conjugated structures facilitate not only the aqueous dispersibility of Ce6, but also the self-accumulation ability of Fe-CDs@Ce6 within melanoma area without requiring extra targets. Moreover, the therapeutic effects of Fe-CDs@Ce6 are synergistically enhanced due to the increased GSH depletion by PDT and the elevated singlet oxygen (1O2) production efficiency by Fe-CDs. When combined with laser irradiation, the tumor growth can be significantly suppressed by Fe-CDs@Ce6 through cyclic administration. The T2-weighted magnetic resonance imaging (MRI) capability of Fe-CDs@Ce6 also reveals their potentials for cancer diagnosis and navigation therapy.

CONCLUSIONS

Our findings indicate the multifunctionality of Fe-CDs@Ce6 in effectively combining ferroptosis/PDT therapy, tumor targeting and MRI imaging, which enables Fe-CDs@Ce6 to become promising biocompatible nanoplatform for the treatment of melanoma.

Rapid and sensitive smartphone non-enzymatic colorimetric assay for the detection of glucose in food based on peroxidase-like activity of Fe3O4@Au nanoparticles

A low-cost and reliable analytical method based on the combination of a newly designed Fe3O4@Au as peroxidase mimetics, supported on smartphone analysis software package was proposed for the determination of glucose content in food samples. The nanocomposite was prepared by self-assembling technique, and the characterization was carried out using transmission electron microscopy (TEM), Fourier transforms infrared, and X-ray diffractometer. Record the color change of the solution with a smartphone camera and optimize the operation parameters and reaction conditions. A smartphone with a free self-developed app was accustomed live the RGB (red-greenblue) values of color intensity within the Fe3O4@Au system and were processed with Image J software before computationally convert them glucose concentrations. At the optimization experiment, reaction temperature of 60 °C, reaction time of 50 min and the amount of addition of Fe3O4@Au 0.0125 g was the optimal combination of detecting glucose smartphone color detection system. Hereon, the accuracy of the proposed method was evaluated by comparison between smartphone colorimetry and UV-vis spectrophotometer, a linear calibration in the range of 0.25 ∼ 15 mmol/L glucose was obtained with minimum detection limit of 1.83 and 2.25 μmol/L, respectively. The proposed method was applied effectively to the detection of glucose in actual samples. The results were in accordance with the conventional UV-vis spectrophotometer method.

Pharmaceutical pollution fingerprinting and waterbodies remediation using waste-derived carbon dots as sustainable advanced nanomaterials

The conversion of biomass waste into high-value nanomaterials such as carbon dots might represent a great advancement towards a circular economy system. Biomass wastes are an excellent choice as carbon precursors because of their wide availability, abundance, chemical composition, and eco-friendly nature. Moreover, their use as a raw material might decrease the total cost of the synthesis processes and reduce the environmental impacts. In addition, the complex composition of biomass leads to carbon dots with abundant functional groups, which in turn enhances water dispersibility and photoluminescence properties. In this manner, the effective transformation of biomass wastes into carbon dots reduces environmental pollution through the inadequate management of waste while producing carbon dots with enhanced performances. Therefore, this review describes biomass wastes as potential candidates for the synthesis of carbon dots through different synthesis methods. In addition, we have analyzed the great potential of biomass-derived carbon dots (CDs) for the degradation and detection of emerging pharmaceutical pollutants by promoting a circular economy approach. Finally, we identified current challenges to propose possible research directions for the large-scale and sustainable synthesis of high-quality biomass-derived CDs.

Tailoring the Surface and Composition of Nanozymes for Enhanced Bacterial Binding and Antibacterial Activity

With the advantages of diverse structures, tunable enzymatic activity, and high stability, nanozymes are widely used in medicine, chemistry, food, environment, and other fields. As an alternative to traditional antibiotics, nanozymes attract more and more attention from the scientific researchers in recent years. Developing nanozymes-based antibacterial materials opens up a new avenue for the bacterial disinfection and sterilization. In this review, the classification of nanozymes and their antibacterial mechanisms are discussed. The surface and composition of nanozymes are critical for the antibacterial efficacy, which can be tailored to enhance both the bacterial binding and the antibacterial activity. On the one hand, the surface modification of nanozymes enables binding and targeting of bacteria that improves the antibacterial performance of nanozymes including the biochemical recognition, the surface charge, and the surface topography. On the other hand, the composition of nanozymes can be modulated to achieve enhanced antibacterial performance including the single nanozyme-mediated synergistic and multiple nanozymes-mediated cascade catalytic antibacterial applications. In addition, the current challenges and future prospects of tailoring nanozymes for antibacterial applications are discussed. This review can provide insights into the design of future nanozymes-based materials for the antibacterial treatments.

Synthesis, properties and mechanism of carbon dots-based nano-antibacterial materials

Antibiotics play an important role in the treatment of diseases, but bacterial resistance caused by their widespread and unreasonable use has become an urgent problem in clinical treatment. With the rapid advancement of nanoscience and nanotechnology, the development of nanomedicine has been transformed into a new approach to the problem of bacterial resistance. As a new type of carbon-based nanomaterial, carbon dots (CDs) have attracted the interest of antibacterial researchers due to their ease of preparation, amphiphilicity, facile surface functionalization, and excellent optical properties, among other properties. This article reviewed the synthesis methods and properties of various CDs and their composites in order to highlight the advancements in the field of CDs-based antibacterial agents. Then we focused on the relationship between the principal properties of CDs and the antibacterial mechanism, including the following: (1) the physical damage caused by the small size, amphiphilicity, and surface charge of CDs. (2) Photogenerated electron transfer characteristics of CDs that produce reactive oxygen species (ROS) in themselves or in other compounds. The ability of ROS to oxidize can lead to the lipid peroxidation of cell membranes, as well as damage proteins and DNA. (3) The nano-enzyme properties of CDs can catalyze reactions that generate ROS. (4) Synergistic antibacterial effect of CDs and antibiotics or other nanocomposites. Finally, we look forward to the challenges that CDs-based nanocomposites face in practical antibacterial applications and propose corresponding solutions to further expand the application potential of nanomaterials in the treatment of infectious diseases, particularly drug-resistant bacterial infections.

Fluoride-activated photothermal system for promoting bacteria-infected wound healing

Although photothermal therapy (PTT) employing nanozymes has shown excellent antibacterial potential, excessive heating generally harms host cells and hinders recovery. Herein, we report an innovative technique for acquiring the programmed temperature by managing the catalytic activity of nanozymes. The photothermal system of CeO2 + F- + TMB can obtain precise photothermal temperature by adjusting the concentration of fluoride ions under near-infrared irradiation. At the optimized photothermal temperature, the photothermal system affords fine photothermal antibacterial treatment with high-efficiency antibacterial effects against Staphylococcus aureus and Escherichia coli in vitro. In vivo wound healing experiments confirm that the system can effectively promote fibroblast proliferation, angiogenesis and collagen deposition with remarkable wound healing efficiency. This strategy offers a novel design concept for creating a new generation of PTT and opens the way for the creation of alternative antibiotics.

Carbon-Based Enzyme Mimetics for Electrochemical Biosensing

Natural enzymes are used as special reagents for the preparation of electrochemical (bio)sensors due to their ability to catalyze processes, improving the selectivity of detection. However, some drawbacks, such as denaturation in harsh experimental conditions and their rapid de- gradation, as well as the high cost and difficulties in recycling them, restrict their practical applications. Nowadays, the use of artificial enzymes, mostly based on nanomaterials, mimicking the functions of natural products, has been growing. These so-called nanozymes present several advantages over natural enzymes, such as enhanced stability, low cost, easy production, and rapid activity. These outstanding features are responsible for their widespread use in areas such as catalysis, energy, imaging, sensing, or biomedicine. These materials can be divided into two main groups: metal and carbon-based nanozymes. The latter provides additional advantages compared to metal nanozymes, i.e., stable and tuneable activity and good biocompatibility, mimicking enzyme activities such as those of peroxidase, catalase, oxidase, superoxide dismutase, nuclease, or phosphatase. In this review article, we have focused on the use of carbon-based nanozymes for the preparation of electrochemical (bio)sensors. The main features of the most recent applications have been revised and illustrated with examples selected from the literature over the last four years (since 2020).

Carbon Dots from Camelina Decorating hFGF2-Linked Camelina Lipid Droplets Cooperate to Accelerate Wound Healing

Constant oxidative stress at the wound site prolongs the inflammation period and slows down the proliferation stage. In order to shorten the inflammatory period meanwhile promote the proliferative activity of fibroblasts, herein, we synthesized novel camelina-derived carbon dots (CDs) decorating on hFGF2-linked camelina lipid droplets (CLD-hFGF2) to form nanobiomaterial CDs-CLD-hFGF2. The CDs-CLD-hFGF2 possesses peroxidase activity and has effective reactive oxygen species radical scavenging activity while achieving proliferation of NIH/3T3 cells under oxidative stress in vitro. In the acute wound model, wound healing after CDs-CLD-hFGF2 treatment reached nearly 92% on the 10th day, compared with 82% for CLD-hFGF2. Moreover, the wound site showed significant anti-inflammatory effects characterized by the downregulation of pro-inflammatory factors and the upregulation of anti-inflammatory factor levels. Overall, this study provided a strategy for the comprehensive utilization of camelina oil crops and revealed a promising future that could be considered an effective method for wound healing on the skin.

Multifunctional Nanoprobe-Amplified Enzyme-Linked Immunosorbent Assay on Capillary: A Universal Platform for Simple, Rapid, and Ultrasensitive Dual-Mode Pathogen Detection

Although the traditional enzyme-linked immunosorbent assay (ELISA) has been widely applied in pathogen detection and clinical diagnostics, it always suffers from complex procedures, a long incubation time, unsatisfying sensitivity, and a single signal readout. Here, we developed a simple, rapid, and ultrasensitive platform for dual-mode pathogen detection based on a multifunctional nanoprobe integrated with a capillary ELISA (CLISA) platform. The novel capture antibodies-modified capillaries can act as a swab to combine in situ trace sampling and detection procedures, eliminating the dissociation between sampling and detection in traditional ELISA assays. With excellent photothermal and peroxidase-like activity, the Fe₃O₄@MoS₂ nanoprobe with a unique p-n heterojunction was chosen as an enzyme substitute and amplified signal tag to label the detection antibody for further sandwich immune sensing. As the analyte concentration increased, the Fe₃O₄@MoS₂ probe could generate dual-mode signals, including remarkable color changes from the chromogenic substrate oxidation as well as photothermal enhancement. Moreover, to avoid false negative results, the excellent magnetic capability of the Fe₃O₄@MoS₂ probe can be used to pre-enrich the trace analytes, amplifying the detection signal and enhancing the immunoassay's sensitivity. Under optimal conditions, specific and rapid detection of SARS-CoV-2 has been realized successfully based on this integrated nanoprobe-enhanced CLISA platform. The detection limits were 5.41 pg·mL^-1 for the photothermal assay and 150 pg·mL^-1 for the visual colorimetric assay. More importantly, the simple, affordable, and portable platform can also be expanded to rapidly detect other targets such as Staphylococcus aureus and Salmonella typhimurium in practical samples, making it a universal and attractive tool for multiple pathogen analysis and clinical testing in the post COVID-19 era.

Magnetic Nanozyme Based on Loading Nitrogen-Doped Carbon Dots on Mesoporous Fe3O4 Nanoparticles for the Colorimetric Detection of Glucose

The simple and accurate monitoring of blood glucose level is of great significance for the prevention and control of diabetes. In this work, a magnetic nanozyme was fabricated based on loading nitrogen-doped carbon dots (N-CDs) on mesoporous Fe₃O₄ nanoparticles for the colorimetric detection of glucose in human serum. Mesoporous Fe₃O₄ nanoparticles were easily synthesized using a solvothermal method, and N-CDs were then prepared in situ and loaded on the Fe₃O₄ nanoparticles, leading to a magnetic N-CDs/Fe₃O₄ nanocomposite. The N-CDs/Fe₃O₄ nanocomposite exhibited good peroxidase-like activity and could catalyze the oxidation of the colorless enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxide (ox-TMB) in the presence of hydrogen peroxide (H₂O₂). When the N-CDs/Fe₃O₄ nanozyme was combined with glucose oxidase (Gox), Gox catalyzed the oxidization of glucose, producing H₂O₂ and leading to the oxidation of TMB under the catalysis of the N-CDs/Fe₃O₄ nanozyme. Based on this mechanism, a colorimetric sensor was constructed for the sensitive detection of glucose. The linear range for glucose detection was from 1 to 180 μM, and the limit of detection (LOD) was 0.56 μM. The recovered nanozyme through magnetic separation showed good reusability. The visual detection of glucose was also realized by preparing an integrated agarose hydrogel containing the N-CDs/Fe₃O₄ nanozyme, glucose oxidase, and TMB. The colorimetric detection platform has an enormous potential for the convenient detection of metabolites.

Rapid in-situ growth of enzyme-mimicking Pd nanoparticles on TEMPO-oxidized nanocellulose for the efficient detection of ascorbic acid

Rapid, efficient and green method of Pd nanoparticles (PdNPs) synthesis on TEMPO-oxidized cellulose nanofibril (TCNF) is demonstrated here. The nanohybrid (PdNPs/TCNF) exhibited peroxidase and oxidase-like activities evident by the oxidation of three chromogenic substrates. Enzyme kinetic studies using 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation uncovered the excellent kinetic parameters (low K_m and high V_max) and good specific activities of 215 U/g and 107 U/g for peroxidase and oxidase-like activities, respectively. A colorimetric assay for ascorbic acid (AA) detection is proposed based on its ability to reduce oxidized TMB to its colorless form. However, presence of nanozyme caused re-oxidation of TMB to its blue colored form within few minutes resulting in time limitation and inaccurate detection. Thanks to the film forming nature of TCNF; this limitation was overcome by employing PdNPs/TCNF film strips that can be easily removed before AA addition. The assay allowed AA detection in the linear range of 0.25-10 μM with a detection limit of 0.039 μM. The results of AA detection in commercial beverages and vitamin C tablets are matching with the specified values. Further the nanozyme exhibited high tolerance to pH (2-10) and temperature (up to 80 °C) and good recyclability for five cycles.

The Key Effect of Carboxyl Group and CuN2 O2 Coordinate Structure for Cu, N Co-Doped Carbon Dots with Peroxidase-Like Property

Carbon dots (CDs) with good water solubility and biocompatibility have become a research hotspot in the nano-enzyme and biomedical field. However, the problems of low catalytic activity and ambiguous catalytic site of CDs as nanozymes still need to be addressed. In this work, CDs loaded with Cu single atoms are obtained through pyrolysis, and the coordination structure and surface functional groups are regulated by adjusting the pyrolysis temperature. CDs obtained at 300 °C (named Cu-CDs-300) have the most carboxyl content and Cu is coordinated in the form of CuN₂ O₂ , which can better decompose H₂ O₂ to produce free radical and is beneficial to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The v_max is 6.56*10^-7  m s^-1 , 6.56 times higher than that of horseradish peroxidase (HRP). Moreover, Cu-CDs-300 can effectively lead to CT26 apoptosis by generating much free radicals. This work demonstrates the synergistic effect of oxygen-containing functional groups and metal coordination structures on peroxide-like activity of CDs and provides new ideas for the design of clear active structure and high efficiency peroxide-like single atom CDs catalyst.

Nanozymes towards Personalized Diagnostics: A Recent Progress in Biosensing

This review highlights the recent advancements in the field of nanozymes and their applications in the development of point-of-care biosensors. The use of nanozymes as enzyme-mimicking components in biosensing systems has led to improved performance and miniaturization of these sensors. The unique properties of nanozymes, such as high stability, robustness, and surface tunability, make them an attractive alternative to traditional enzymes in biosensing applications. Researchers have explored a wide range of nanomaterials, including metals, metal oxides, and metal-organic frameworks, for the development of nanozyme-based biosensors. Different sensing strategies, such as colorimetric, fluorescent, electrochemical and SERS, have been implemented using nanozymes as signal-producing components. Despite the numerous advantages, there are also challenges associated with nanozyme-based biosensors, including stability and specificity, which need to be addressed for their wider applications. The future of nanozyme-based biosensors looks promising, with the potential to bring a paradigm shift in biomolecular sensing. The development of highly specific, multi-enzyme mimicking nanozymes could lead to the creation of highly sensitive and low-biofouling biosensors. Integration of nanozymes into point-of-care diagnostics promises to revolutionize healthcare by improving patient outcomes and reducing costs while enhancing the accuracy and sensitivity of diagnostic tools.

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 K_m and V_max 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.

One-pot hydrothermal synthesis of metal-doped carbon dot nanozymes using protein cages as precursors

Metal-doped carbon dots represent a new class of promising nanomaterials with enzyme-like activity, whose properties such as fluorescence properties and enzyme-like activity are determined by the precursors and the conditions used to prepare them. Nowadays, the synthesis of carbon dots using naturally occurring precursors has attracted increasing attention. Here, using metal-loaded horse spleen ferritin as a precursor, we report a facile one-pot hydrothermal strategy to synthesise metal-doped fluorescent carbon dots with enzyme-like activity. The as-prepared metal-doped carbon dots exhibit high water solubility, uniform size distribution, and good fluorescence. In particular, the Fe-doped carbon dots exhibit prominent oxidoreductase catalytic activities, including peroxidase-like, oxidase-like, catalase-like, and superoxide dismutase-like activities. This study provides a green synthetic strategy for developing metal-doped carbon dots with enzymatic catalytic activity.

Antibacterial Carbon Dots-Based Composites

The emergence and global spread of bacterial resistance to conventionally used antibiotics have highlighted the urgent need for new antimicrobial agents that might replace antibiotics. Currently, nanomaterials hold considerable promise as antimicrobial agents in anti-inflammatory therapy. Due to their distinctive functional physicochemical characteristics and exceptional biocompatibility, carbon dots (CDs)-based composites have attracted a lot of attention in the context of these antimicrobial nanomaterials. Here, a thorough assessment of current developments in the field of antimicrobial CDs-based composites is provided, starting with a brief explanation of the general synthesis procedures, categorization, and physicochemical characteristics of CDs-based composites. The many processes driving the antibacterial action of these composites are then thoroughly described, including physical destruction, oxidative stress, and the incorporation of antimicrobial agents. Finally, the obstacles that CDs-based composites now suffer in combating infectious diseases are outlined and investigated, along with the potential applications of antimicrobial CDs-based composites.

Metal-Based Nanozymes with Multienzyme-Like Activities as Therapeutic Candidates: Applications, Mechanisms, and Optimization Strategy

Most nanozymes in development for medical applications only exhibit single-enzyme-like activity, and are thus limited by insufficient catalytic activity and dysfunctionality in complex pathological microenvironments. To overcome the impediments of limited substrate availabilities and concentrations, some metal-based nanozymes may mimic two or more activities of natural enzymes to catalyze cascade reactions or to catalyze multiple substrates simultaneously, thereby amplifying catalysis. Metal-based nanozymes with multienzyme-like activities (MNMs) may adapt to dissimilar catalytic conditions to exert different enzyme-like effects. These multienzyme-like activities can synergize to realize "self-provision of the substrate," in which upstream catalysts produce substrates for downstream catalytic reactions to overcome the limitation of insufficient substrates in the microenvironment. Consequently, MNMs exert more potent antitumor, antibacterial, and anti-inflammatory effects in preclinical models. This review summarizes the cellular effects and underlying mechanisms of MNMs. Their potential medical utility and optimization strategy from the perspective of clinical requirements are also discussed, with the aim to provide a theoretical reference for the design, development, and therapeutic application of their catalytic effects.

A critical review on the environmental applications of carbon dots

The discovery of zero-dimensional carbonaceous nanostructures called carbon dots (CDs) and their unique properties associated with fluorescence, quantum confinement and size effects have intrigued researchers. There has been a substantial increase in the amount of research conducted on the lines of synthesis, characterization, modification, and enhancement of properties by doping or design of composite materials, and a diversification of their applications in sensing, catalysis, optoelectronics, photovoltaics, and imaging, among many others. CDs fulfill the need for inexpensive, simple, and continuous environmental monitoring, detection, and remediation of various contaminants such as metals, dyes, pesticides, antibiotics, and other chemicals. The principles of green chemistry have also prompted researchers to rethink novel modes of nanoparticle synthesis by incorporating naturally available carbon precursors or developing micro reactor-based techniques. Photocatalysis using CDs has introduced the possibility of utilizing light to accelerate redox chemical transformations. This comprehensive review aims to provide the reader with a broader perspective of carbon dots by encapsulating the concepts of synthesis, characterization, applications in contaminant detection and photocatalysis, demerits and research gaps, and potential areas of improvement.

Downregulation of Peroxidase Activity of Platinum Cube Enables Minute-Time Scale Colorimetric Signaling of Hypoxanthine for Fish Freshness Monitoring

Due to its unique biological composition, aquatic products, especially fish, are extremely perishable compared to other muscle products. Herein, we proposed an artificial nanozyme-based colorimetric detection of hypoxanthine (Hx), the indicator of fish freshness, in a minute-time scale without the assistance of a natural enzyme (hypoxanthine oxidase). The principle is based on the interaction between Hx and polyvinylpyrrolidone-modified platinum cubic nanomaterials (PVP-PtNC), in which the catalytic active sites of PVP-PtNC's surface were blocked by Hx. This causes the downregulation of PVP-PtNC's catalytic ability and weakened its ability to catalyze the oxidization of 3,3',5,5'-Tetramethylbenzidine (TMB) by H₂O₂. Accordingly, the decrease in the UV-vis absorption and the weakening of the colorimetric reaction color is proportional to the Hx concentration. On this basis, a target-triggered colorimetric method for detecting Hx is developed for fish freshness monitoring with a fast detection speed, low cost, high accuracy, and simplified operation. Experiments reveal that the correlation response of Hx is from 0.5 μM to 10 mM with a limit of detection of 0.16 μM. In particular, the Hx detected from real fish indicates that the method possesses a promising potential for practical application. All of these features are expected to promote the development of online detection tools for food safety monitoring.

Flow injection spectrophotometric determination total antioxidant capacity in human serum samples based on response surface methodology to optimize synthesized peroxidase-like activity carbon dots

Total antioxidant capacity (TAC) is an important indicator for evaluating oxidative stress of the human body. Since TAC is related to the concentration of reducing substances, it can be detected by using peroxidase-like or oxidase-like activity of nanozyme materials. In this work, the cobalt and nitrogen co-doped carbon dots (Co/N-CDs) are fabricated for building stability and high peroxidase-like nanozyme through the Box-Behnken design of response surface methodology. The morphology and luminescence properties of obtained Co/N-CDs were characterized by TEM and fluorophotometer, respectively. Interestingly, the surface charge of Co/N-CDs are innovatively investigated by a simple and widespread gel electrophoresis, which holds the potential to be an alternative to Zeta potential analysis. In addition, a flow injection spectrophotometric assay to detect ascorbic acid is develop with a high sensitivity and automation based on a Co/N-CDs/guaiacol/H₂O₂ catalytic reaction system. The proposed method is also responsive to other reducing substances such as cysteine and glutathione. Therefore, the presented sensor can realize the determination of TAC, and then, some actual human serum samples are detected accurately and quickly (the recovery rates are 93.46-105.61 %).