Synthesis of N, Zn-doped carbon dots for the detection of Fe3+ ions and bactericidal activity against Escherichia coli and Staphylococcus aureus

Seizing the Hidden Assassin: Current Detection Strategies for Staphylococcus aureus and Methicillin-Resistant S. aureus

Staphylococcus aureus (S. aureus) is a kind of pathogenic bacteria which can lead to food poisoning, hospital, and community infections. S. aureus and methicillin-resistant S. aureus (MRSA) have become headaches for public health worldwide. Therefore, strengthening the detection of S. aureus and MRSA is a critical step to prevent and control its spread and infection. This review summarized multiple detection methods (electrochemical, optical, and other biosensors) for sensitive and efficient detection of nonresistant and resistant S. aureus. First, we have introduced the principle and methods of detection platform for S. aureus and MRSA. We also contrasted various detection strategies. Finally, the current situation and prospect of S. aureus and MRSA detection in the future are explored in depth, and its development direction of detection methods is also predicted. In this review, we found that although biosensors have shown tremendous brilliance in the field of monitoring, they are currently in the experimental stage. It can be certain that we are very close to entering the commercialization stage. The point-of care testing available to nonprofessionals will become a new direction. We firmly believe that the monitoring system will be more perfect and stable and public life will be healthier and safer.

Designed fluorescence "on-off-on" probe based on cobalt, zinc, and nitrogen co-doped graphene quantum dots: A case of quinalphos sensing

In this study, we developed a new fluorescence "on-off-on" sensor utilizing water-soluble cobalt/zinc-nitrogen co-doped graphene quantum dots (Co/Zn-N-GQDs) to recognize quinalphos pesticide in vegetable and fruit samples. Primarily, the synthesis method employed a one-pot hydrothermal approach, using betel leaves as a natural precursor and cobalt ("Co"), zinc ("Zn"), and urea ("N") as dopant sources. The Co/Zn-N-GQDs probes underwent comprehensive analytical characterization. The Co/Zn-N-GQDs were synthesized with a remarkable luminescence yield of 31.49%, exhibiting excitation at 320 nm and emission peak at 393 nm. Interestingly, the luminescence of Co/Zn-N-GQDs was selectively "Turned Off" by Cu2+ via a static quenching setup. Remarkably, quenched fluorescence was surprisingly reactivated upon adding quinalphos to the quench setup, indicating a direct correlation between luminescence reactivation and quinalphos concentration. Briefly, this phenomenon is ascribed to the functional groups in quinalphos, such as quinoxalinyl and phosphorothioate, which chelate with Cu2+ ions, disrupting the nonfluorescent Cu2+-Co/Zn-N-GQDs complex. The design sensor demonstrated a limit of detection (LOD) of 0.11 μM and a broad linear span of 0.5 to 200 μM. In conclusion, Cu2+-Co/Zn-N-GQDs sensor showed immediate applicability, stability, and reproducibility, making it highly effective for quinalphos sensing in various samples.

Cellulose nanofiber-based multifunctional composite films integrated with zinc doped-grapefruit peel-based carbon quantum dots

This study aimed to develop a multifunctional active composite film to extend the shelf life of minced pork. The composite film was prepared by incorporating zinc-doped grapefruit peel-derived carbon quantum dots (Zn-GFP-CD) into a cellulose nanofiber (CNF) matrix. The resulting film significantly improved UV-blocking properties from 39.0 % to 85.7 % while maintaining the film transparency. Additionally, the CNF/Zn-GFP-CD5% composite film exhibits strong antioxidant activity with ABTS and DPPH radical scavenging activities of 99.8 % and 77.4 %, respectively. The composite film also showed excellent antibacterial activity against both Gram-negative and Gram-positive bacteria. When used in minced pork packaging, the composite films effectively inhibit bacterial growth, maintaining bacterial levels below 7 Log CFU/g after 15 days and sustaining a red color over a 21-day storage period. Additionally, a significant reduction in the lipid oxidation of the minced pork was observed. These CNF/Zn-GFP-CD composite films have a great potential for active food packaging applications to extend shelf life and maintain the visual quality of packaged meat.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Preventing biofilm formation and eradicating pathogenic bacteria by Zn doped histidine derived carbon quantum dots

Bacterial infections are of major medical concern due to antibiotic resistance. Carbon quantum dots (CDs) have emerged as potentially excellent biomaterials for multifunctional applications due to their low toxicity, outstanding water solubility, high fluorescence, and high biocompatibility. All of these properties allow CDs to be exceptional biomaterials for inhibiting the growth of bacteria and stopping biofilm formation due to their strong binding affinity, cell wall penetration, and solubilizing biofilm in water. Here, we describe a strategy for one-pot synthesis of histidine-derived zinc-doped N-doped CDs (Zn-NCDs) by a hydrothermal method for inhibiting the growth of both Gram-positive and Gram-negative bacteria without harming mammalian cells. The NCDs and Zn-NCDs showed uniform sizes (∼6 nm), crystallinity, good photostability, high quantum yield (76%), and long decay time (∼5 ns). We also studied their utilization for live cell bio-imaging and the antimicrobial properties towards the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa. Importantly, the Zn-NCDs could penetrate the biofilm and bacterial cell wall to effectively inhibit the growth of bacteria and subsequently inhibit biofilm formation. Thus, the structure, chemical composition, and low toxicity properties of the newly-developed Zn-NCDs exemplify a promising novel method for the preparation of nano-level antibacterial drugs.

Cobalt-modulated dual emission carbon dots for ratiometric fluorescent vancomycin detection

This work presents a simple yet selective fluorometric protocol for the quantification of vancomycin, an important antibiotic for treating infections caused by Gram-positive bacteria. A novel ratiometric fluorometric method for the determination of vancomycin is developed based on dual emissive carbon dots (DECDs) with emission at 382 nm and 570 nm in combination with Co2+ ions. Upon addition of Co2+ions, the fluorescence at 382 nm of DECDs is enhanced while emission at 570 nm remains constant. In the presence of vancomycin, it complexes with Co2+ leading to quenching of the 382 nm fluorescence due to strong binding with Co2+ in the Co@DECDs system. The DECDs are fully characterized by TEM and different spectroscopic techniques. The proposed ratiometric method is based on measuring fluorescence ratio (F570/F382) against vancomycin concentration and the method exhibits a good linearity range from 0.0 to 120.0 ng mL-1 with a low limit of detection (S/N = 3) of 0.31 ng mL-1. The method shows good selectivity with minimal interference from potential interfering species. This ratiometric fluorometric approach provides a promising tool for sensitive and specific vancomycin detection in clinical applications.

Carrageenan-based multifunctional packaging films containing Zn-carbon dots/anthocyanin derived from Kohlrabi peel for monitoring quality and extending the shelf life of shrimps

Carrageenan-based active/intelligent packaging films containing anthocyanin and ZnO-doped CD (Zn-CD) from purple Kohlrabi peels were prepared for freshness monitoring and shelf-life extension of shrimp, and the influence of additives on the films' physical, functional, and structural properties was investigated. The films showed excellent UV blocking ability (85.2% of UV-A and 99.4% of UV-B) and high antioxidant effect (∼99% for ABTS and ∼ 58.6% for DPPH radical scavenging activity) and showed strong antibacterial activity to stop the growth (100%) of L. monocytogenes and to reduce the growth of E. coli by 8.1 log CFU/mL after 12 h of incubation. In shrimp packaging experiments, the films were evident in the freshness monitoring, reduced spoilage, and increased shelf life. This study suggests that next-generation biopolymer films impregnated with biomass-derived CDs and natural colorants will provide broad directions for ensuring safety and extending shelf life to meet the accelerating demand for packaging products.

Synthesis of high quantum yield rhenium-doped carbonized polymer dots for dual sensing of Fe3+ and Mo6+ and anti-counterfeit ink applications

The bottom-up approach serves as an efficacious and noteworthy method for the synthesis of carbonized polymer dots (CPDs). In the present investigation, rhenium-doped CPDs (Re-CPDs) were successfully synthesized via a hydrothermal technique employing citric acid, urea, and NH4ReO4. Subsequent to a comprehensive series of characterizations, Re-CPDs demonstrated an average particle size of 2.67 nm, excitation/emission maxima of 377/461 nm, and an elevated quantum yield of 45.36% at 377 nm excitation. Through the selectivity analysis involving various metal ions, Re-CPDs displayed sensitivity towards Fe3+ and Mo6+ ions, with limits of detection (LODs) of 0.02 μM and 0.48 μM, respectively. Furthermore, Re-CPDs exhibited multi-chromatic fluorescence (450-550 nm) under excitation wavelengths (375-430 nm). As a result, by amalgamating Re-CPDs with sucrose, detection patterns capable of generating multi-chromatic fluorescence at excitation wavelengths of 375, 395, and 430 nm, respectively, were successfully devised. In summary, Re-CPDs hold considerable potential as a material for the detection of Fe3+ and Mo6+ ions, as well as for anti-counterfeiting ink applications.

Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization

Nitrogen-doped carbon dots (CDs) have attracted considerable attention across various research areas and applications due to their enhanced optical properties and photostability. However, the mechanism of nitrogen incorporation in CDs remains elusive, hampering the precise control over nitrogen-incorporated structures and the investigation of the effects of nitrogen on the electronic structure and optical properties of CDs. In this study, we employed a rational design approach, utilizing glucosamine and ethylene glycol as the carbon source and co-reagent, respectively, to synthesize N-doped CDs. Our synthesis strategy involved pinacol rearrangement and iminium ion cyclization reactions, enabling the reliable formation of N-doped CDs. Notably, the resulting CDs exhibited distinctive emissive states attributed to heteroatomic defect structures, including oxygenic and nitrogenic polycyclic aromatic hydrocarbons. To gain further insights into their energy levels and electronic transitions, we conducted comprehensive investigations, employing extended Hückel calculations and pump-probe spectroscopy. The synthesized CDs displayed great promise as bioimaging and photodynamic therapy agents, highlighting their potential for biomedical applications. Moreover, our study significantly contributes valuable insights into the rational design of N-doped CDs with controllable chemical and electronic structures, thereby paving the way for advancements in their diverse range of applications.

Effect of a new slow-release zinc fertilizer based on carbon dots on the zinc concentration, growth indices, and yield in wheat (Triticum aestivum)

The present study aimed to introduce a new carbon dots nanocarrier (Zn-NCDs) as a slow-release Zn fertilizer. Zn-NCDs was synthesized using a hydrothermal method and characterized by instrumental methods. A greenhouse experiment was then conducted involving two Zn sources (Zn-NCDs and ZnSO₄), three concentrations of Zn-NCDs (2, 4, and 8 mg/L), and under sand culture conditions. This study comprehensively evaluated the effects of Zn-NCDs on the zinc, nitrogen, and phytic acid content, biomass, growth indices, and yield in bread wheat (cv. Sirvan). Also, a fluorescence microscope was used to examine the in vivo transport route of Zn-NCDs in wheat organs. Finally, the availability of Zn in soil samples treated with Zn-NCDs was evaluated over 30 days in an incubation experiment. The findings indicated that Zn-NCDs as a slow-release fertilizer increased root-shoot biomass, fertile spikelet, and grain yield by 20, 44, 16, and 43%, respectively, compared to ZnSO₄ treatment. The concentration of zinc and nitrogen in the grain was increased by 19% and 118%, respectively, while phytic acid was decreased by 18% than ZnSO₄ treatment. Microscopic observations revealed that wheat plants could absorb and transfer Zn-NCDs from roots to stems and leaves through vascular bundles. This study demonstrated for the first time that Zn-NCDs could be used as a slow-release Zn fertilizer with high efficiency and low cost in wheat enrichment. In addition, Zn-NCDs could be applied as a new nano fertilizer and technology for in vivo plant imaging.

Nitrogen-doped carbon dots: Recent developments in its fluorescent sensor applications

Doped carbon dots have attracted great attention from researchers across disciplines because of their unique characteristics, such as their low toxicity, physiochemical stability, photostability, and outstanding biocompatibility. Nitrogen is one of the most commonly used elements for doping because of its sizeable atomic radius, strong electronegativity, abundance, and availability of electrons. This distinguishes them from other atoms and allows them to perform distinctive roles in various applications. Here, we have reviewed the most current breakthroughs in nitrogen-doped CDs (N-CDs) for fluorescent sensor applications in the last five years. The first section of the article addresses several synthetic and sustainable ways of making N-CDs. Next, we briefly reviewed the fluorescent features of N-CDs and their sensing mechanism. Furthermore, we have thoroughly reviewed their fluorescent sensor applications as sensors for cations, anions, small molecules, enzymes, antibiotics, pathogens, explosives, and pesticides. Finally, we have discussed the N-CDs' potential future as primary research and how that may be used. We hope that this study will contribute to a better understanding of the principles of N-CDs and the sensory applications that they can serve.

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.

N,Zn-Doped Fluorescent Sensor Based on Carbon Dots for the Subnanomolar Detection of Soluble Cr(VI) Ions

The development of a fluorescent sensor has attracted much attention for the detection of various toxic pollutants in the environment. In this work, fluorescent carbon dots (N,Zn-CDs) doped with nitrogen and zinc were synthesized using citric acid monohydrate and 4-pyridinecarboxyaldehyde as carbon and nitrogen sources, respectively. The synthesized N,Zn-CDs served as an "off" fluorescence detector for the rapid and sensitive detection of hexavalent chromium ions (Cr(VI)). The zinc metal integrated into the heteroatomic fluorescent carbon dot played a functional role by creating a coordination site for the hydrogen ions that were displaced after the addition of Cr to the solution matrix. The stepwise addition of Cr(VI) effectively quenched the fluorescence intensity of the N,Zn-CDs, and this phenomenon was attributed to the internal filter effect. A low detection limit of 0.47 nmol/L for Cr(VI) was achieved in the fluorescence experiments. Real water samples were used to evaluate the practical application of N,Zn-CDs for the quantification of Cr(VI). The results show acceptable recoveries and agreement with ion chromatography-ultraviolet spectrometry results. These good recoveries indicate that the fluorescence probe is very well suited for environmental measurements.

Carboxymethylcellulose/agar-based functional film incorporated with nitrogen-doped polyethylene glycol-derived carbon dots for active packaging applications

The present investigation demonstrates the role of nitrogen doping on polyethylene glycol (PEG)-derived carbon dots on optical, antibacterial, and antioxidant activity. CDs' average size and surface charge were determined using transmission electron microscopy (TEM) and a zeta sizer with 2.14 ± 0.6 nm and -20 mV, respectively. Though CDs without N-doping (PCD) did not show any significant antioxidant and antimicrobial activities, the CDs doped with nitrogen (NPCD) showed potent antioxidant (25% and 100% DPPH and ABTS radical scavenging activity) and significant antimicrobial activity against Gram-positive (1.8 cm inhibition zone) and Gram-negative (1.4 cm) bacteria. Both carbon dots were loaded into the carboxymethyl cellulose (CMC)/agar-based film with different concentrations (4 and 8%) and showed a significant increase in the physicochemical properties, and UV-blocking property was increased from 53.7 to 79.9% without sacrificing the transparency. The NPCD-loaded film also showed high antioxidant (DPPH 12.7% and ABTS 67%) and potent antibacterial activity. In particular, the CMC/agar film loaded with 8% NPCD destroyed Escherichia coli and Listeria monocytogenes completely after 6 h of incubation.

Advances and prospects of carbon dots for microplastic analysis

Microplastics have become the world's most emerging pollutants today due to the ubiquitous use of plastics in everyday life and their ability to migrate from micro to nanoscale to every corner of the natural world, leading to ecological imbalances and global catastrophes. However, a standardized method for separating and analyzing microplastics from actual food or environmental samples has not been established. Therefore, it is necessary to develop a simple, fast, cost-effective, and accurate method that can accurately measure the degree of contamination of microplastics. As one of these methods, fluorometry has been proposed as a cost-effective method to detect, quantify and differentiate individual plastic particles. Therefore, this review discussed the technique for analyzing microplastics using fluorescent carbon dots (CDs). This review provided an overview of the impact of microplastics and the feasibility of using CDs to detect and analyze microplastics. In particular, this review will discuss novel microplastic analysis methods using CD and future application studies. The method using CDs will overcome the limitations of current microplastic analysis technology and may become a new method for detecting and analyzing microplastics.

Functional Carbon Quantum Dots for Ocular Imaging and Therapeutic Applications

Carbon quantum dots (CDs) are a class of emerging carbonaceous nanomaterials that have received considerable attention due to their excellent fluorescent properties, extremely small size, ability to penetrate cells and tissues, ease of synthesis, surface modification, low cytotoxicity, and superior water dispersion. In light of these properties, CDs are extensively investigated as candidates for bioimaging probes, efficient drug carriers, and disease diagnostics. Functionalized CDs represent a promising therapeutic candidate for ocular diseases. Here, this work reviews the potential use of functionalized CDs in the diagnosis and treatment of eye-related diseases, including the treatment of macular and anterior segment diseases, as well as targeting Aβ amyloids in the retina.

Fabrication of Carbon-Based Quantum Dots via a "Bottom-Up" Approach: Topology, Chirality, and Free Radical Processes in "Building Blocks"

The discovery of carbon-based quantum dots (CQDs) has allowed opportunities for fluorescence bioimaging, tumor diagnosis and treatment, and photo-/electro-catalysis. Nevertheless, in the existing reviews related to the "bottom-up" approaches, attention is mainly paid to the applications of CQDs but not the formation mechanism of CQDs, which mainly derived from the high complexities during the synthesis of CQDs. Among the various synthetic methods, using small molecules as "building blocks", the development of a "bottom-up" approach has promoted the structural design, modulation of the photoluminescence properties, and control of the interfacial properties of CQDs. On the other hand, many works have demonstrated the "building blocks"-dependent properties of CQDs. In this review, from one of the most important variables, the relationships among intrinsic properties of "building blocks" and photoluminescence properties of CQDs are summarized. The topology, chirality, and free radical process are selected as descriptors for the intrinsic properties of "building blocks". This review focuses on the induction and summary of recent research results from the "bottom-up" process. Moreover, several empirical rules pertaining thereto are also proposed.

Emerging and Versatile Platforms of Metal-Ion-Doped Carbon Dots for Biosensing, Bioimaging, and Disease Therapy

Metal ions possess abundant electrons and unoccupied orbitals, as well as large atomic radii, whose doping into carbon dots (CDs) is a facile strategy to endow CDs with additional physicochemical characteristics. After being doped with metal ions, CDs reveal obvious changes in their optical, electronic, and magnetic properties by adjustments to their electron density distribution and the energy gaps, leading them to be promising and competitive candidates as labeling probes, imaging agents, catalysts, nanodrugs, and so on. In this review, we summarize the fabrication methods of metal-ion-doped CDs (M-CDs), and highlight their biological applications including biosensing, bioimaging, tumor therapy, and anti-microbial treatment. Finally, the challenging future perspectives of M-CDs are analyzed. We hope this review will provide inspiration for further development of M-CDs in various biological aspects, and help readers who are interested in M-CDs and their biological applications.

Highly efficient carbon dots for quantitatively visualizing pH fluctuations in cells, zebrafish, mice and tumors

In vivo pH is closely related to complicated physiological and pathological processes. Quantitatively probing pH and visualizing pH variation via fluorescence (FL) imaging technique in living cells and organisms is crucial but difficult to accomplish. Herein, green fluorescent carbon dots (CDs) were synthesized, and their distinct advantages of extraordinarily high fluorescence quantum yield (FQY, 71.4%), unique photostability, high selectivity, sterling biocompatibility, appropriate pKa for biosensing, enable CDs to serve as pH-activatable probes for real time quantitative detection of continuous pH fluctuation in living cells, zebrafish, mice and tumors. We believe CDs are presently among the best-of-breed pH probes for comprehensive biomedical applications.

Zn-assisted modification of the chemical structure of N-doped carbon dots and their enhanced quantum yield and photostability

This article presents the Zn-assisted synthesis of N-doped carbon dots (N-CDs) with an enhanced quantum yield (QY) and photostability. There have been intensive studies to improve or tune the optical properties of carbon dots (CDs) to meet the demand for luminescent materials in various fields, including energy conversion, photocatalysis, bioimaging, and phototherapy. For these applications, the photostability of the CDs is also a critical factor, but the related studies are relatively less common. The Zn-assisted N-CDs (denoted as Zn:N-CDs) obtained by the addition of Zn(OAc)₂ to the precursors during the synthesis of N-CDs not only exhibited an enhanced quantum yield but also improved photostability compared to those of N-CDs. A comprehensive study of the chemical composition of Zn:N-CD and N-CD using X-ray photoelectron spectroscopy indicated a correlation between their chemical structure and photostability. Zn(OAc)₂, which acts as a catalytic reagent, induced the modification of chemical structures at the edges of carbogenic sp² domains, without being doped in N-CD, and the heteroatom-carbon bonds in Zn:N-CD seemed to be more resistant to light compared to those in N-CDs. The increased QY and photostability of Zn:N-CDs make them more suitable as an optical probe and they could be used in fingerprint identification. With Zn:N-CDs, the microstructure of fingerprints was confirmed clearly for a long duration effectively.

Synthesis of Doped/Hybrid Carbon Dots and Their Biomedical Application

Carbon dots (CDs) are a novel type of carbon-based nanomaterial that has gained considerable attention for their unique optical properties, including tunable fluorescence, stability against photobleaching and photoblinking, and strong fluorescence, which is attributed to a large number of organic functional groups (amino groups, hydroxyl, ketonic, ester, and carboxyl groups, etc.). In addition, they also demonstrate high stability and electron mobility. This article reviews the topic of doped CDs with organic and inorganic atoms and molecules. Such doping leads to their functionalization to obtain desired physical and chemical properties for biomedical applications. We have mainly highlighted modification techniques, including doping, polymer capping, surface functionalization, nanocomposite and core-shell structures, which are aimed at their applications to the biomedical field, such as bioimaging, bio-sensor applications, neuron tissue engineering, drug delivery and cancer therapy. Finally, we discuss the key challenges to be addressed, the future directions of research, and the possibilities of a complete hybrid format of CD-based materials.

Modification strategies of membranes with enhanced Anti-biofouling properties for wastewater Treatment: A review

This review addresses composite membranes used for wastewater treatment, focusing heavily on the anti-biofouling properties of such membranes. Biofouling caused by the development of a thick biofilm on the membrane surface is a major issue that reduces water permeance and reduces its lifetime. Biofilm formation and adhesion are mitigated by modifying membranes with two-dimensional or zero-dimensional carbon-based nanomaterials or their modified substituents. In particular, nanomaterials based on graphene, including graphene oxide and carbon quantum dots, are mainly used as nanofillers in the membrane. Functionalization of the nanofillers with various organic ligands or compositing the nanofiller with other materials, such as silver nanoparticles, enhances the bactericidal ability of composite membranes. Moreover, such membrane modifications reduce biofilm adhesion while increasing water permeance and salt/dye rejection. This review discusses the recent literature on developing graphene oxide-based and carbon quantum dot-based composite membranes for biofouling-resistant wastewater treatment.

Recent Advances in Nanozymes for Bacteria-Infected Wound Therapy

Bacterial-infected wounds are a serious threat to public health. Bacterial invasion can easily delay the wound healing process and even cause more serious damage. Therefore, effective new methods or drugs are needed to treat wounds. Nanozyme is an artificial enzyme that mimics the activity of a natural enzyme, and a substitute for natural enzymes by mimicking the coordination environment of the catalytic site. Due to the numerous excellent properties of nanozymes, the generation of drug-resistant bacteria can be avoided while treating bacterial infection wounds by catalyzing the sterilization mechanism of generating reactive oxygen species (ROS). Notably, there are still some defects in the nanozyme antibacterial agents, and the design direction is to realize the multifunctionalization and intelligence of a single system. In this review, we first discuss the pathophysiology of bacteria infected wound healing, the formation of bacterial infection wounds, and the strategies for treating bacterially infected wounds. In addition, the antibacterial advantages and mechanism of nanozymes for bacteria-infected wounds are also described. Importantly, a series of nanomaterials based on nanozyme synthesis for the treatment of infected wounds are emphasized. Finally, the challenges and prospects of nanozymes for treating bacterial infection wounds are proposed for future research in this field.

Carbon dot composites for bioapplications: a review

Recent advancements in the synthesis of carbon dot composites and their applications in biomedical fields (bioimaging, drug delivery and biosensing) have been carefully summarized. The current challenges and future trends of CD composites in this field have also been discussed.

Iron ion sensing and in vitro and in vivo imaging based on bright blue-fluorescent carbon dots

Herein, we propose an eco-friendly synthesis of carbon dots (CDs) and ingeniously design a rapid and label-free "turn-off" sensing platform for ultrasensitive recognition of Fe³⁺ in vitro and in vivo. CDs with extraordinary advantages involving exceptional stability, ultra-low toxicity as well as admirable biocompatibility were simply prepared via one-step hydrothermal strategy of Caulis polygoni multiflora. Result indicated that as-acquired CDs not only exhibit excitation dependency, but also have a high quantum yield of (QY) up to 42%. Miraculously, the fluorescence of CDs can be extinguished sharply by Fe³⁺ because of static quenching effect with linear range of 0-400 µM, yielding a detection limit of 0.025 μM. Benefiting from these characteristics, CDs have been extended for multicolourful imaging and tracking Fe³⁺ fluctuations in living cells. Bioimaging of zebrafish larvae exposed to CDs confirmed that it is smoothly circulated to other tissues and organs owing to their small size. Eventually, as-prepared CDs have been implemented for the real-time detection of Fe³⁺ in nude mice.

Anchoring zinc-doped carbon dots on a paper-based chip for highly sensitive fluorescence detection of copper ions

In this work, zinc-doped carbon dots (Zn-CDs) were anchored on a three-dimensional wheel type paper-based microfluidic chip, and were decorated with 6-mercaptonicotinic acid (MNA) and L-cysteine (L-Cys) for highly sensitive and rapid fluorescence detection of Cu²⁺. Zn-CDs were first anchored on paper through the amide bonds between the carboxyl groups of the Zn-CDs and the amino groups of the paper. Afterwards, Zn-CDs were decorated with MNA and L-Cys, effectively preventing the Zn-CDs from aggregation. The nitrogen atom on the pyridine ring and the carboxylic acid groups in MNA and L-Cys coordinated with Cu²⁺ to form a nonfluorescent ground-state complex, causing the fluorescence quenching of the Zn-CDs. The three-dimensional rotary design could simplify the operation process and achieve simultaneous analysis of multiple samples with different concentrations. Under optimal conditions, the fluorescent sensor exhibits linear response for the determination of Cu²⁺ in the range from 0.1 to 60 μg L^-1 with the detection limit (LOD) of 0.018 μg L^-1. The proposed strategy provides a novel way for the highly sensitive detection of Cu²⁺ in a complex water environment.

Construction of Enhanced Photostability Anthraquinone-Type Nanovesicles Based on a Novel Two-Step Supramolecular Assembly Strategy and Their Application on Multiband Laser-Responsive Composites

The photostability and dispersity under aggregation states always become an obstacle for the development of small-molecular organic dye (SMOD) composites. Herein, a novel supramolecular assembly strategy with a two-step assembly method is implemented to encapsulate SMODs for improving their photostability and acquiring uniformly dispersed nanoaggregates in aqueous solution. By the novel assembly strategy, photodegradation rates of the anthraquinone-type dyes can decrease significantly, and the stability of dispersed nanoassembly bodies can be improved in solution. Based on the two-step supramolecular assembly strategy, a new kind of aqueous processing composite system can be developed for preparing multiband laser-responsive devices and in situ healing of optical composite films. This two-step supramolecular assembly strategy can provide a new template and reference for improving the defects of SMODs and fabricating high-performance optical devices.

Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

Facile one-pot synthesis of multifunctional protamine sulfate-derived carbon dots for antibacterial applications and fluorescence imaging of bacteria

PS-carbon dots (CDs) were prepared by a microwave-assisted method using protamine sulfate (PS), and they have dual functions of antibacterial and bacterial imaging.

An ultrasensitive chemiluminescence assay for 4-nitrophenol by using luminol-NaIO4 reaction catalyzed by copper, nitrogen co-doped carbon dots

A chemiluminescence (CL) assay on the basis of the tremendous enhancing effect of copper and nitrogen co-doped carbon dots (Cu,N-CDs) on the luminol-NaIO₄ reaction was introduced for the determination of nanomolar levels of 4-nitrophenol (4-NP). Cu,N-CDs were synthesized by a hydrothermal approach and characterized by TEM, XRD, EDX, and FTIR analysis. The potential CL mechanism was elucidated by recording the CL spectrum and by evaluating the influence of reactive oxygen species. It was found that 4-NP remarkably inhibited the luminol-NaIO₄-Cu,N-CDs reaction and reduced the CL signal of the reaction. This fact was applied for developing a CL assay for 4-NP. Under the optimized conditions, 4-NP could be determined in the concentration range of 0.25 to 150 nM, with a detection limit as low as 0.06 nM. This assay was successfully exploited for the analysis of 4-NP in real environmental samples.

Nanozymes used for antimicrobials and their applications

Bacterial infection-related diseases have been growing year-by-year rapidly and raising health problems globally. The exploitation of novel, high efficiency, and bacteria-binding antibacterial agents are extremely need. As far as now, the most extensive treatment is restricted to antibiotics, which may be overused and misused, leading to increased multidrug resistance. Antibiotics abuse, as well as antibiotic-resistance of bacteria, is a global challenge in the current situation. It is highly recommended and necessary to develop novel bactericide to kill the bacteria effectively without causing further resistance development and biosafety issues. Nanozymes, inorganic nanostructures with intrinsic enzymatic activities, have attracted more and more interest from the researchers owing to their exceptional advantages. Compared to natural enzymes, nanozymes can destroy many Gram-positive, Gram-negative bacteria, which builds an important bridge between biology and nanotechnology. As the potent nanoantibiotics, nanozymes have exciting broad-spectrum antimicrobial properties and negligible biotoxicities. And we summarized and highlighted the recent advances on nanozymes including its antibacterial mechanism and applications. Finally, challenges and limitations for the further improvement of the antibacterial activity are covered to provide future directions for the use of engineered nanozymes with enhanced antibacterial function.