Selective Labeling and Growth Inhibition of Pseudomonas aeruginosa by Aminoguanidine Carbon Dots

Constructing a highly efficient multifunctional carbon quantum dot platform for the treatment of infectious wounds

Antibiotic resistance poses a huge threat to public health, which has increased the difficulty and transmission of disease treatment, as well as the burden and cost of medical institutions. In response to the current problems and challenges in inflammation control and treatment of bacterial infected wounds, inspired by antibacterial mechanisms based on active elements such as N, S, Cu and tannic acid (TA), a highly efficient multifunctional carbon quantum dot platform was proposed in this study and constructed through their special assembly in a solvothermal reaction system for the treatment of infected wounds. By introducing active elements such as N, S and Cu, this carbon quantum dot platform is endowed with antibacterial properties, while also achieving good angiogenesis promoting performance through the use of ion Cu. Meanwhile, the good antioxidant activity of TA (one of the precursors used) enables this platform to have better immunomodulatory performance in vivo. The research results on the treatment of bacterial infection models indicate that the multifunctional carbon quantum dots obtained can accelerate the healing of infected wounds by inhibiting bacterial infection, regulating immunoreaction, accelerating collagen deposition and promoting angiogenesis. This multifunctional carbon quantum dot platform shows good clinical application prospects in treating bacterial infected wounds. Additionally, the fluorescence characteristics of such carbon dots can be expected to realize visual therapy in the future.

Emerging trends and future challenges of advanced 2D nanomaterials for combating bacterial resistance

The number of multi-drug-resistant bacteria has increased over the last few decades, which has caused a detrimental impact on public health worldwide. In resolving antibiotic resistance development among different bacterial communities, new antimicrobial agents and nanoparticle-based strategies need to be designed foreseeing the slow discovery of new functioning antibiotics. Advanced research studies have revealed the significant disinfection potential of two-dimensional nanomaterials (2D NMs) to be severed as effective antibacterial agents due to their unique physicochemical properties. This review covers the current research progress of 2D NMs-based antibacterial strategies based on an inclusive explanation of 2D NMs' impact as antibacterial agents, including a detailed introduction to each possible well-known antibacterial mechanism. The impact of the physicochemical properties of 2D NMs on their antibacterial activities has been deliberated while explaining the toxic effects of 2D NMs and discussing their biomedical significance, dysbiosis, and cellular nanotoxicity. Adding to the challenges, we also discussed the major issues regarding the current quality and availability of nanotoxicity data. However, smart advancements are required to fabricate biocompatible 2D antibacterial NMs and exploit their potential to combat bacterial resistance clinically.

Carbon Nanodot-Microbe-Plant Nexus in Agroecosystem and Antimicrobial Applications

The intensive applications of nanomaterials in the agroecosystem led to the creation of several environmental problems. More efforts are needed to discover new insights in the nanomaterial-microbe-plant nexus. This relationship has several dimensions, which may include the transport of nanomaterials to different plant organs, the nanotoxicity to soil microbes and plants, and different possible regulations. This review focuses on the challenges and prospects of the nanomaterial-microbe-plant nexus under agroecosystem conditions. The previous nano-forms were selected in this study because of the rare, published articles on such nanomaterials. Under the study's nexus, more insights on the carbon nanodot-microbe-plant nexus were discussed along with the role of the new frontier in nano-tellurium-microbe nexus. Transport of nanomaterials to different plant organs under possible applications, and translocation of these nanoparticles besides their expected nanotoxicity to soil microbes will be also reported in the current study. Nanotoxicity to soil microbes and plants was investigated by taking account of morpho-physiological, molecular, and biochemical concerns. This study highlights the regulations of nanotoxicity with a focus on risk and challenges at the ecological level and their risks to human health, along with the scientific and organizational levels. This study opens many windows in such studies nexus which are needed in the near future.

Selective Bacterial Growth Inactivation by pH-Sensitive Sulfanilamide Functionalized Carbon Dots

Carbon dots (CDs) were synthesized hydrothermally by mixing citric acid (CA) and an antifolic agent, sulfanilamide (SNM), employed for pH sensing and bacterial growth inactivation. Sulfanilamide is a prodrug; aromatic hetero cyclization of the amine moiety along with other chemical modifications produces an active pharmacological compound (chloromycetin and miconazole), mostly administered for the treatment of various microbial infections. On the other hand, the efficacy of the sulfanilamide molecule as a drug for antimicrobial activity was very low. We anticipated that the binding of the sulfanilamide molecule on the carbon dot (CD) surface may form antibacterial CDs. Citric acid was hybridized with sulfanilamide during the hydrothermal preparation of the CDs. The molecular fragments of bioactivated sulfanilamide molecule play a crucial role in bacterial growth inactivation for Gram-positive and Gram-negative bacteria. The functional groups of citric acid and sulfanilamide were conserved during the CD formation, facilitating the zwitterionic behavior of CDs associated with its photophysical activity. At low concentrations of CDs, the antibacterial activity was apparent for Gram-positive bacteria only. This Gram-positive bacteria selectivity was also rationalized by zeta potential measurement.

Biofilm Inhibition on Medical Devices and Implants Using Carbon Dots: An Updated Review

Biofilms are an intricate community of microbes that colonize solid surfaces, communicating via a quorum-sensing mechanism. These microbial aggregates secrete exopolysaccharides facilitating adhesion and conferring resistance to drugs and antimicrobial agents. The escalating global concern over biofilm-related infections on medical devices underscores the severe threat to human health. Carbon dots (CDs) have emerged as a promising substrate to combat microbes and disrupt biofilm matrices. Their numerous advantages such as facile surface functionalization and specific antimicrobial properties, position them as innovative anti-biofilm agents. Due to their minuscule size, CDs can penetrate microbial cells, inhibiting growth via cytoplasmic leakage, reactive oxygen species (ROS) generation, and genetic material fragmentation. Research has demonstrated the efficacy of CDs in inhibiting biofilms formed by key pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Consequently, the development of CD-based coatings and hydrogels holds promise for eradicating biofilm formation, thereby enhancing treatment efficacy, reducing clinical expenses, and minimizing the need for implant revision surgeries. This review provides insights into the mechanisms of biofilm formation on implants, surveys major biofilm-forming pathogens and associated infections, and specifically highlights the anti-biofilm properties of CDs emphasizing their potential as coatings on medical implants.

Light-Induced Self-Assembled Polydiacetylene/Carbon Dot Functional "Honeycomb"

The design of functional supramolecular assemblies from individual molecular building blocks is a fundamental challenge in chemistry and material science. We report on the fabrication of "honeycomb" films by light-induced coassembly of diacetylene derivatives and carbon dots. Specifically, modulating noncovalent interactions between the carbon dots, macrocyclic diacetylene, and anthraquinone diacetylene facilitates formation of thin films exhibiting a long-range, uniform pore structure. We show that light irradiation at distinct wavelengths plays a key role in the assembly process and generation of unique macro-porous morphology, by both initiating interactions between the carbon dots and the anthraquinone moieties and giving rise to the topotactic polymerization of the polydiacetylene network. We further demonstrate utilization of the macro-porous film as a photocatalytic platform for water pollutant degradation and as potential supercapacitor electrodes, both applications taking advantage of the high surface area, hydrophobicity, and pore structure of the film.

Modifying cellulose fibres with carbon dots: a promising approach for the development of antimicrobial fibres

This study focuses on the development of antimicrobial fibres for use in medical and healthcare textile industries. Carbon dots (CDs) were designed with boronic acid groups for the attachment to cellulose fibres found in cotton textiles and to enhance their attachment to glycogens on bacterial surfaces. Boronic acid-based and curcumin-based CDs were prepared and characterized using various techniques, showing a nanoscale size and zeta potential values. The CDs inhibited the growth of both Staphylococcus epidermidis and Escherichia coli bacteria, with UV-activated CDs demonstrating improved antibacterial activity. The antimicrobial activity of the CDs was then tested, revealing strong adherence to cellulose paper fibres with no CD diffusion and potent inhibition of bacterial growth. Cytotoxicity assays on human cell lines showed no toxicity towards cells at concentrations of up to 100 µg ml-1 but exhibited increased toxicity at concentrations exceeding 1000 µg ml-1. However, CD-modified cellulose paper fibres showed no toxicity against human cell lines, highlighting the antimicrobial properties of the CD-modified cellulose fibres are safe for human use. These findings show promising potential for applications in both industrial and clinical settings.

Boric Acid-Functionalized Carbon Dots as a High-Performance Antibacterial Agent against Escherichia coli

Bacterial infections and antibiotic abuse are a global threat to human health. In recent years, there has been a boom in research on antimicrobial agents with low toxicity and efficient nanomaterials. Boric acid-functionalized carbon dots (B-CDs) with negative surface charge were synthesized by the hydrothermal method. Covalent bonds were formed between the boric acid groups and the cis-diol groups of the polysaccharide in the bacterial cell wall, and numerous B-CDs were trapped on the bacterial surface. In the experiments of antibacterial activity, B-CDs presented strong bactericidal activity against Escherichia coli (E. coli) with a minimum bactericidal concentration of 12.5 μg/mL. The antibacterial mechanism suggested that B-CDs entered the cell interior by diffusion and posed significant damage to the double helix structure of E. coli DNA. Furthermore, B-CDs exhibited low toxicity. The results demonstrated that the novel antimicrobial B-CDs not only fought against E. coli infection and antibiotic misuse but also provided new ideas for safe and effective antimicrobial agents of carbon nanomaterials.

AuNP-Loaded Electrospinning Membrane Cooperated with CDs for Periodontal Tissue Engineering

BACKGROUND

Guided bone regeneration (GBR) is commonly used to regenerate periodontal tissue. However, the bone inductivity and antibacterial properties of the GBR membranes currently in use are severely limited. This issue can be resolved by loading growth factors and antibiotics. Bioactive substitutes, such as Au nanoparticles (AuNPs) and carbon quantum dots (CDs), were proposed to prevent the denaturation of osteogenic growth factors and the induction of antibacterial drug resistance.

METHODS

Ornidazole was initially used as the raw material to prepare the CDs, followed by the incorporation of an optimal ratio of nanoparticles to produce the electrospun membrane doped with AuNPs and novel traceable antibacterial CDs. The morphology of the membrane was characterized. The adhesion, proliferation, and osteogenic differentiation of cells on the membrane were evaluated in vitro. The antimicrobial characteristics of the membrane were also investigated. The electrospun membrane was implanted into a rat skull defect model in vivo to investigate its osteogenic potential.

RESULTS

The blending of nanomaterials did not affect the micro morphology of the fiber, resulting in enhanced mechanical properties. Membranes doped with AuNPs and CDs exhibited excellent biocompatibility, increased ALP activity, improved calcified nodules, and increased expression of osteogenic-associated proteins, in addition to pronounced antibacterial effects. The membrane also demonstrated excellent osteogenic characteristics in rat models.

CONCLUSION

The synergistic effect of loaded AuNPs electrospun fiber membrane with CDs can promote periodontal bone regeneration and exert antibacterial activity.

A novel fluorescent traceable carbon quantum dots with selective antibacterial activity against Porphyromonas gingivalis

Antibiotics can kill bacteria, but their continued use can easily lead to drug resistance, particularly the main pathogenic bacteria of periodontitis, Porphyromonas gingivalis. However, to avoid drug resistance, carbon quantum dots (CDs) have great potential as a bioactive material in antimicrobial therapy. Herein, we use ornidazole as raw material to prepare CDs of different sizes by microwave irradiation and screen CDs with fluorescence and bacteriostatic properties. The inhibition experiments and live/dead assays of P. gingivalis exhibited outstanding antibacterial effects. This research aimed to develop nano-level antibacterial active materials that also have fluorescence traceability. This study offers a different method for the development of multifunctional CDs, provides valuable strategies for the treatment of diseases associated with P. gingivalis, and predicts great application prospects in the field of biomedicine.

High energy density storage, antifungal activity and enhanced bioimaging by green self-doped heteroatom carbon dots

Self-heteroatom-doped N-carbon dots (N-CDs) with a 2.35 eV energy gap and a 65.5% fluorescence quantum yield were created using a one-step, efficient, inexpensive, and environmentally friendly microwave irradiation method. FE-SEM, EDX, FT-IR, XRD, UV-VIS spectroscopy, FL spectroscopy, and CV electrochemical analysis were used to characterise the produced heteroatom-doped N-CDs. The graphitic carbon dot surface is doped with heteroatom functional groups such (S, P, K, Mg, Zn) = 1%, in addition to the additional passivating agent (N), according to the EDX surface morphology and the spontaneous heteroatom doping was caused by the heterogeneous chemical composition of pumpkin seeds. These spontaneous heteroatom-doped N-CDs possess quasispherical amorphous graphitic structure with an average size of less than 10 nm and the interplaner distance of 0.334 nm. Calculations utilising cyclic voltammetry showed that the heteroatom-doped N-CDs placed on nickel electrodes had a high specific capacitance value of 1044 F/g at a scan rate of 10 mV/s in 3 M of KOH electrolyte solution. Furthermore, it demonstrated a high energy and power density of 28.50 Wh/kg and 3350 W/kg, respectively. The higher value of specific capacitance and energy density were attributed to the fact that the Ni/CDs electrode material possesses both EDLC and PC properties due to the sufficient surface area and the multiple active sites of the prepared N-CDs. Furthermore, the heteroatom N-CDs revealed the antifungal action and bioimaging of the "Cladosporium cladosporioides" mould, which is mostly accountable for economic losses in agricultural products. The functional groups of nitrogen, sulphur, phosphorus, and zinc on the surface of the CDs have strong antibacterial and antifungal properties as well as fluorescence enhanced bioimaging.

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.

Antibacterial Carbon Dots: Mechanisms, Design, and Applications

The increase in antibiotic resistance promotes the situation of developing new antibiotics at the forefront, while the development of non-antibiotic pharmaceuticals is equally significant. In the post-antibiotic era, nanomaterials with high antibacterial efficiency and no drug resistance make them attractive candidates for antibacterial materials. Carbon dots (CDs), as a kind of carbon-based zero-dimensional nanomaterial, are attracting much attention for their multifunctional properties. The abundant surface states, tunable photoexcited states, and excellent photo-electron transfer properties make sterilization of CDs feasible and are gradually emerging in the antibacterial field. This review provides comprehensive insights into the recent development of CDs in the antibacterial field. The topics include mechanisms, design, and optimization processes, and their potential practical applications are also highlighted, such as treatment of bacterial infections, against bacterial biofilms, antibacterial surfaces, food preservation, and bacteria imaging and detection. Meanwhile, the challenges and outlook of CDs in the antibacterial field are discussed and proposed.

Size-dependent antibacterial of carbon dots by selective absorption and differential oxidative stress of bacteria

Carbon dots (CDs), as one kind of zero-dimensional carbon-based nanomaterials, show great potential in combating emerging infectious diseases and antimicrobial infections. CDs with outstanding optical properties and benign biocompatibility have been reported as excellent antibacterial agents. However, few reports were focused on the relationship between the CDs' size and their antibacterial activity. Herein, the desired CDs (VCDs) were fabricated by a one-step electrochemical oxidation method using l-ascorbic acid as raw material, and four types of VCDs with different sizes were obtained by adjusting the reaction times. The effectiveness of antibacterial activity demonstrates the VCDs display size-dependent antibacterial activity, where the VCDs-2 (average size: 2.92 nm) exhibit superior antibacterial activity to others, attributing to the synergy of the absorption capacity of bacteria to VCDs and the ROS stimulated by VCDs. The VCDs-2 could more easily penetrate bacterial cells, stimulate the production of ROS, damage the cell walls of E. coli, and inhibit the growth and reproduction of bacteria. This work helps to understand the effect of CDs' size on antibacterial properties, and provides a direction for the design of novel antimicrobials with drug resistance.

Guanidine-Functionalized Fluorescent sp2 Carbon-Conjugated Covalent Organic Framework for Sensing and Capture of Pd(II) and Cr(VI) Ions

Palladium is a key element in fuel cells, electronic industries, and organic catalysis. At the same time, chromium is essential in leather, electroplating, and metallurgical industries. However, their unpremeditated leakage into aquatic systems has caused human health and environmental apprehensions. Herein, we reported the development of an sp² carbon-conjugated fluorescent covalent organic framework with a guanidine moiety (sp² c-gCOF) that showed excellent thermal and chemical stability. The sp² c-gCOF showed effective sensing, capture, and recovery/removal of Pd(II) and Cr(VI) ions, which could be due to the highly accessible pore walls decorated with guanidine moieties. The fluorescent sp² c-gCOF showed higher selectivity for Pd(II) and Cr(VI) ions, with an ultra-low detection limit of 2.7 and 3.2 nM, respectively. The analysis of the adsorption properties with a pseudo-second-order kinetic model showed that sp² c-gCOF could successfully and selectively remove both Pd(II) and Cr(VI) ions from aqueous solutions. The polymer also showed excellent capture efficacy even after seven consecutive adsorption-desorption cycles. Hence, this study reveals the potential of fluorescent sp² c-gCOF for detecting, removing, and recovering valuable metals and hazardous ions from wastewater, which would be useful for economic benefit, environmental safety, human health, and sustainability. The post-synthetic modification of sp² c-COF with suitable functionalities could also be useful for sensing and extracting other water pollutants and valuable materials from an aqueous system.

Antibacterial and antibiofilm mechanisms of carbon dots: a review

Due to the increasing bacterial resistance to conventional antibiotics, developing safe and effective approaches to combat infections caused by bacteria and biofilms has become an urgent clinical problem. Recently, carbon dots (CDs) have received great attention as a promising alternative to conventional antimicrobial agents due to their excellent antimicrobial efficacy and biocompatibility. Although CDs have been widely used in the field of antibacterial applications, their antibacterial and antibiofilm mechanisms have not been systematically discussed. This review provides a systematic overview on the complicated mechanisms of antibacterial and antibiofilm CDs based on recent development.

Broad-Spectrum Antibacterial Activity of Synthesized Carbon Nanodots from d-Glucose

Carbon nanodots, a class of carbon nano-allotropes, have been synthesized through different routes and methods from a wide range of precursors. The selected precursor, synthetic method, and conditions can strongly alter the physicochemical properties of the resulting material and their intended applications. Herein, carbon nanodots (CNDs) have been synthesized from d-glucose by combining pyrolysis and chemical oxidation methods. The effect of the pyrolysis temperature, equivalents of oxidizing agent, and refluxing time were studied on the product and quantum yield. In the optimum conditions (pyrolysis temperature of 300 °C, 4.41 equiv of H2O2, 90 min of reflux) CNDs were obtained with 40% and 3.6% of product and quantum yields, respectively. The obtained CNDs are negatively charged (ζ-potential = -32 mV), excellently dispersed in water, with average diameter of 2.2 nm. Furthermore, ammonium hydroxide (NH4OH) was introduced as dehydrating and/or passivation agent during CNDs synthesis resulting in significant improvement of both product and quantum yields of about 1.5 and 3.76-fold, respectively. The synthesized CNDs showed a broad spectrum of antibacterial activities toward different Gram-positive and Gram-negative bacteria strains. Both synthesized CNDs caused highly colony forming unit reduction (CFU), ranging from 98% to 99.99% for most of the tested bacterial strains. However, CNDs synthesized in the absence of NH4OH, due to a negatively charged surface enriched in oxygenated groups, performed better in zone inhibition and minimum inhibitory concentration. The elevated antibacterial activity of high-oxygen-containing carbon nanodots is directly correlated to their ROS formation ability.

Aminoglycoside-mimicking carbonized polymer dots for bacteremia treatment

Bacteremia and associated bacterial sepsis are potentially fatal and occur when the host response to microbial invasion is impaired or compromised. This motivated us to develop carbonized polymer dots (CPDs_Man/AA) from a mixture of mannose (Man) and positively charged amino acids [AAs; lysine, arginine (Arg), or histidine] through a one-step mild pyrolysis procedure, which effectively inhibited drug-resistant bacterial strains isolated from septic patients. The as-prepared CPDs_Man/AA showed broad-spectrum antibacterial activity, including multidrug-resistant bacteria, even in human plasma. The minimal inhibitory concentration of CPDs_Man/Arg is ca. 1.0 μg mL^-1, which is comparable to or lower than those of other tested antibiotics (e.g., ampicillin, gentamicin, and vancomycin). In addition to directly disrupting bacterial membranes, the CPDs_Man/Arg feature a structure similar to aminoglycoside antibiotics that could bind to 16S rRNA, thereby blocking bacterial protein synthesis. In vitro cytotoxic and hemolytic assays demonstrated the high biocompatibility of the CPDs_Man/AA. In addition, in vivo studies on methicillin-resistant Staphylococcus aureus-infected mice treated with the CPDs_Man/Arg showed a significant decrease in mortality-even better than that of antibiotics. Overall, the synthesis of the CPDs_Man/AA is cost-efficient, straightforward, and effective for treating bacteremia. The polymeric features of the CPDs_Man/Arg, including cationic charges and specific groups, can be recognized as a safe and broad-spectrum biocide to lessen our reliance on antibiotics to treat systemic bacterial infections in the future.

Carbon Dots in Biomedicine: A Review

Despite the rapid development of science and technology, the effective treatment of cancer still threatens human life and health. However, the success of cancer treatment is closely related to early diagnosis, identification, and effective treatment. In recent years, with the strengthening of the development and research of nanomaterials for cancer diagnosis and treatment, researchers have found that carbon dots (CDs) have the advantages of wide absorption, excellent biocompatibility, diverse imaging characteristics, and photostability and are widely used in various fields, such as sensing, imaging, and drug/gene transportation. Recently, researchers also discovered that CDs could be used as an effective photosensitizer to generate active oxygen or convert light energy into heat under the stimulation of the external lasers, making them have the effects of photothermal and photodynamic therapy for cancer. In this review, we first outline the single-modal and multimodal imaging analysis of CDs in cancer cells. After introducing diversified imaging functions, we focused on the design and the latest research progress of CDs in phototherapy and introduced in detail the strategies of CDs in phototherapy treatment and the challenges faced by clinical applications. We hope that this overview can provide important insights for researchers and accelerate the pace of research on CDs in imaging-guided phototherapy treatment.

Quaternized carbon quantum dots with broad-spectrum antibacterial activity for the treatment of wounds infected with mixed bacteria

Bacterial resistance to antibiotics have become one of the most severe threats in global public health, so the development of new-style antimicrobial agents is urgent. In this work, quaternized carbon quantum dots (qCQDs) with broad-spectrum antibacterial activity were synthesized by a simple green "one-pot" method using dimethyl diallyl ammonium chloride and glucose as reaction precursors. The qCQDs displayed satisfactory antibacterial activity against both Gram-positive and gram-negative bacteria. In rat models of wounds infected with mixed bacteria, qCQDs obviously restored the weight of rats, significantly reduced the death of rats from severe infection, and promoted the recovery and healing of infected wounds. Biosafety tests confirmed that qCQDs had no obvious toxic and side effects during the testing stage. The analysis of quantitative proteomics revealed that qCQDs mainly acted on ribosomal proteins in Staphylococcus aureus (Gram-positive bacteria) and significantly down-regulated proteins associated with citrate cycle in Escherichia coli (Gram-negative bacteria). Meanwhile, real-time quantitative PCR confirmed that the variation trend of genes corresponding to the proteins associated with ribosome and citrate cycle was consistent with the proteomic results after treatment of qCQDs, suggesting that qCQDs has a new antibacterial mechanism which is different from the reported carbon quantum dots with antibacterial action. STATEMENT OF SIGNIFICANCE: With the development of the research on carbon quantum dots, the application of carbon quantum dots in the field of medicine has attracted extensive attention. In this paper, quaternized carbon quantum dots (qCQDs) with antimicrobial activity prepared by specific methods were studied, including antimicrobial spectrum, antimicrobial mechanism and in vivo antimicrobial application. The antimicrobial mechanism of qCQDs was studied by proteomics and RT-qRCR, and the different mechanisms of qCQDs against Gram-positive and Gram-negative bacteria were also found. This study provides a research foundation for the application of carbon quantum dots in antimicrobial field, and also expands the application range of carbon quantum dots in medicine field.

Probing the chemical constituents of Cassia javanica and its in vitro analyses as a potent drug

The phytochemical screening of the crude methanolic stem extracts of Cassia javanica plant showed the presence of different classes of organic compounds like alkaloids, tannins, flavonoids, saponins, phlobatanins, steroids, anthraquinone and cardiac glycoside. The starching frequencies of these functional groups were determined from FT-IR spectroscopic data. The crude and their fractions were examined for antibacterial potential against Klebsiella pneumoniae and Proteus mirabilis. The antibacterial assay showed maximum zone of inhibition for ethyl acetate fraction, i.e. 20 mm against Proteus mirabilis and 18 mm against Klebsiella pneumoniae in the comparison with Levofloxacin used as standard (40 mm). Meanwhile for methanolic crude extract, the inhibition zone was recorded 14 mm against Klebsiella pneumoniae and 22 mm against Proteus mirabilis. The minimum inhibitory concentrations and minimum bactericidal concentrations were recorded as 187.5 µg ml^-1 against Proteus mirabilis and 93.75 µg ml^-1 against Klebsiella pneumoniae. The scavenging free radical assay was noted as 69.61% at the concentration of 100 ppm.

Nanotechnology in combating biofilm: A smart and promising therapeutic strategy

Since the birth of civilization, people have recognized that infectious microbes cause serious and often fatal diseases in humans. One of the most dangerous characteristics of microorganisms is their propensity to form biofilms. It is linked to the development of long-lasting infections and more severe illness. An obstacle to eliminating such intricate structures is their resistance to the drugs now utilized in clinical practice (biofilms). Finding new compounds with anti-biofilm effect is, thus, essential. Infections caused by bacterial biofilms are something that nanotechnology has lately shown promise in treating. More and more studies are being conducted to determine whether nanoparticles (NPs) are useful in the fight against bacterial infections. While there have been a small number of clinical trials, there have been several in vitro outcomes examining the effects of antimicrobial NPs. Nanotechnology provides secure delivery platforms for targeted treatments to combat the wide range of microbial infections caused by biofilms. The increase in pharmaceuticals' bioactive potential is one of the many ways in which nanotechnology has been applied to drug delivery. The current research details the utilization of several nanoparticles in the targeted medication delivery strategy for managing microbial biofilms, including metal and metal oxide nanoparticles, liposomes, micro-, and nanoemulsions, solid lipid nanoparticles, and polymeric nanoparticles. Our understanding of how these nanosystems aid in the fight against biofilms has been expanded through their use.

Advances in the Methods for the Synthesis of Carbon Dots and Their Emerging Applications

Cutting-edge technologies are making inroads into new areas and this remarkable progress has been successfully influenced by the tiny level engineering of carbon dots technology, their synthesis advancement and impressive applications in the field of allied sciences. The advances of science and its conjugation with interdisciplinary fields emerged in carbon dots making, their controlled characterization and applications into faster, cheaper as well as more reliable products in various scientific domains. Thus, a new era in nanotechnology has developed into carbon dots technology. The understanding of the generation process, control on making processes and selected applications of carbon dots such as energy storage, environmental monitoring, catalysis, contaminates detections and complex environmental forensics, drug delivery, drug targeting and other biomedical applications, etc., are among the most promising applications of carbon dots and thus it is a prominent area of research today. In this regard, various types of carbon dot nanomaterials such as oxides, their composites and conjugations, etc., have been garnering significant attention due to their remarkable potential in this prominent area of energy, the environment and technology. Thus, the present paper highlights the role and importance of carbon dots, recent advancements in their synthesis methods, properties and emerging applications.

A Targeted Photosensitizer Mediated by Visible Light for Efficient Therapy of Bacterial Keratitis

Bacterial keratitis is a serious bacterial infection of the cornea that can cause sight loss in severe cases because of the sharp decline of efficacious antibiotics. Herein, a targeted photosensitizer based on BODIPY severing as a photobactericidal agent was developed for treating bacterial keratitis. The water solubility of the material was as high as 10 mg/mL, which was attributable to the introduction of pathogen-targeting galactose and fucose. The photosensitizer was able to preferentially bind Pseudomonas aeruginosa instead of mammalian cells and trigger the aggregation of bacteria, which ultimately facilitated effective pathogen ablation upon the generation of reactive oxygen species (ROS) via laser irradiation. Photoexcited targeted photosensitizers can promote wound healing by eradicating P. aeruginosa in rat eyes and reducing the inflammatory response, thus exhibiting the significant therapeutic effect on bacterial keratitis. We also performed molecular level mechanistic studies using the unique field-induced droplet ionization mass spectrometry methodology and confirmed that the generated ROS were mainly singlet oxygen that caused lipid peroxidation (Type II mechanism). We anticipate that the targeted photosensitizer will have great potential in the application of clinical photodynamic therapy to ocular infection.

Carbon Dots as an Emergent Class of Antimicrobial Agents

Antimicrobial resistance is a recognized global challenge. Tools for bacterial detection can combat antimicrobial resistance by facilitating evidence-based antibiotic prescribing, thus avoiding their overprescription, which contributes to the spread of resistance. Unfortunately, traditional culture-based identification methods take at least a day, while emerging alternatives are limited by high cost and a requirement for skilled operators. Moreover, photodynamic inactivation of bacteria promoted by photosensitisers could be considered as one of the most promising strategies in the fight against multidrug resistance pathogens. In this context, carbon dots (CDs) have been identified as a promising class of photosensitiser nanomaterials for the specific detection and inactivation of different bacterial species. CDs possess exceptional and tuneable chemical and photoelectric properties that make them excellent candidates for antibacterial theranostic applications, such as great chemical stability, high water solubility, low toxicity and excellent biocompatibility. In this review, we will summarize the most recent advances on the use of CDs as antimicrobial agents, including the most commonly used methodologies for CD and CD/composites syntheses and their antibacterial properties in both in vitro and in vivo models developed in the last 3 years.

Carbon Quantum Dots Derived from Different Carbon Sources for Antibacterial Applications

Nanoparticles possess unique features due to their small size and can be composed of different surface chemistries. Carbon quantum dots possess several unique physico-chemical and antibacterial activities. This review provides an overview of different methods to prepare carbon quantum dots from different carbon sources in order to provide guidelines for choosing methods and carbon sources that yield carbon quantum dots with optimal antibacterial efficacy. Antibacterial activities of carbon quantum dots predominantly involve cell wall damage and disruption of the matrix of infectious biofilms through reactive oxygen species (ROS) generation to cause dispersal of infecting pathogens that enhance their susceptibility to antibiotics. Quaternized carbon quantum dots from organic carbon sources have been found to be equally efficacious for controlling wound infection and pneumonia in rodents as antibiotics. Carbon quantum dots derived through heating of natural carbon sources can inherit properties that resemble those of the carbon sources they are derived from. This makes antibiotics, medicinal herbs and plants or probiotic bacteria ideal sources for the synthesis of antibacterial carbon quantum dots. Importantly, carbon quantum dots have been suggested to yield a lower chance of inducing bacterial resistance than antibiotics, making carbon quantum dots attractive for large scale clinical use.

Broad-Spectrum Photo-Antimicrobial Polymers Based on Cationic Polystyrene and Rose Bengal

New strategies to fight bacteria and fungi are necessary in view of the problem of iatrogenic and nosocomial infections combined with the growing threat of increased antimicrobial resistance. Recently, our group has prepared and described two new readily available materials based on the combination of Rose Bengal (singlet oxygen photosensitizer) and commercially available cationic polystyrene (macroporous resin Amberlite® IRA 900 or gel-type resin IRA 400). These materials showed high efficacy in the antimicrobial photodynamic inactivation (aPDI) of Pseudomonas aeruginosa. Here, we present the photobactericidal effect of these polymers against an extended group of pathogens like Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, and the opportunistic yeast Candida albicans using green light. The most interesting finding is that the studied materials are able to reduce the population of both Gram-positive and Gram-negative bacteria with good activity, although, for C. albicans, in a moderate manner. In view of the results achieved and especially considering the inexpensiveness of these two types of photoactive polymers, we believe that they could be used as the starting point for the development of coatings for self-disinfecting surfaces.

Hydrothermal synthesis of N-doped carbon quantum dots and their application in ion-detection and cell-imaging

Carbon quantum dots (CQDs), owing to their characteristic luminescent properties, have become a new favorite in the field of luminescence. They have been widely used in light emitting diode, ion detection, cell-imaging, ect. Herein a facile synthesis method of nitrogen-doped carbon quantum dots (N-CQDs) has been developedviaa one-step hydrothermal of glucose and m-phenylenediamine. The chemical composition, surface functional groups, and crystal structure of so prepared N-CQDs were systematically characterized. The characterizations indicate that nitrogen has been chemically doped in the CQDs and the N-CQDs crystallize in a graphene structure. Photoluminescence (PL) measurements show that the N-CQDs emit strong blue emission under the irradiation of ultraviolet. The emission is excitation-dependent, is resistant to photo bleaching and high ionic strength, and slightly decreases with the increase of temperature. The quantum yield of them is about 17.5%. The PL intensity of N-CQDs quenches linearly with the increase of the concentrations of Fe³⁺(0.5-1.0 mM) and CrO₄^2-(0.3-0.6 mM), which are a kind of excellent fluorescent probe for the detection of Fe³⁺ and CrO₄^2-. The quenching mechanism of Fe³⁺ and CrO₄^2-is verified to be a static quenching mechanism based on inner filter effect. The N-CQDs are also found to be a good cell-imaging reagent of Hela cells.

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.

Biocompatible Carbon Quantum Dots Derived from Sugarcane Industrial Wastes for Effective Nonlinear Optical Behavior and Antimicrobial Activity Applications

In this work, the green synthesis of highly fluorescent carbon quantum dots (CQDs) with an efficient quantum yield of 17.98% using sugarcane bagasse pulp as the precursor was conducted by a hydrothermal technique. The high-resolution transmission electron microscopy analysis revealed that the CQDs were competently monodispersed with the particle size ranging between 0.75 and 2.75 nm. The structural properties of CQDs were investigated using X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses. The UV-visible spectrum showed two absorption peaks due to the aromatic C=C transitions of π-π* and C=O transitions of n-π*. The fluorescence spectrum of CQDs displayed a strong blue emission. However, the first-ever of its kind, sugarcane industrial solid waste carbon quantum dots caused significant orders to obey the enhancement of the third-order nonlinearity (χ(3)) when compared with other carbon dots (CDs). The calculated nonlinear optical (NLO) parameters such as n 2, β, and χ(3) were 1.012 × 10-8 cm2/W, 2.513 × 10-4, and 3.939 × 10-7 esu, respectively. The figures of merit were evaluated to be W = 6.6661 and T = 0.0132, which greatly fulfilled the optical switching conditions. Besides, the antibacterial activities of CQDs were screened against aquatic Gram-positive (Benthesicymus cereus and Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa, Vibrio cholerae, and Escherichia coli) microbial organisms. Our findings, however, indicate that synergistic sugarcane industrial waste CQDs are promising materials for the functioning of NLO devices, bioimaging, and pharmaceutical applications.

Preparation of two types of silver-doped fluorescent carbon dots and determination of their antibacterial properties

The preparation and performance of doped antibacterial carbon dots (CDs) have been the research hotspot. In this paper, we report the preparation of two blue light-emitting silver-doped CDs, CD-1 and CD-2, through one- and two-step routes, respectively, by using polyethyleneimine, citric acid, and AgNO₃ as raw materials. Both CDs exhibited excellent and broad-spectrum activity against gram-positive bacteria, gram-negative bacteria, and fungi. We compared the emission wavelength, surface group, particle size, chargeability, and element content of the two CDs through various characterization methods. CD-2 exhibiting longer emission wavelength, larger particle size, and higher silver content displayed higher antibacterial activity against microorganisms than CD-1. On the other hand, CDs exhibited varying antibacterial properties against different microorganisms because of differences in the cell wall structure of gram-positive bacteria (peptidoglycan), gram-negative bacteria (lipopolysaccharides), and fungi (chitin). Based on scanning electron microscopy observations, circular dichroism spectroscopy and agarose gel electrophoresis, we speculate that CDs exert antibacterial activity mainly through membrane disruption and their effect on intracellular DNA and proteins. At the same time, CDs have multicolor imaging capabilities of Staphylococcus aureus. The antibacterial activity and versatility of bioimaging make them more potential antibacterial agents than traditional agents.

Insight into the effect of particle size distribution differences on the antibacterial activity of carbon dots

Carbon dots (CDs) have a profound effect on elimination of bacteria, fungi, and viruses, but the lack of an exact mechanism to interact with bacterial cells limits their development. Herein, we separated the CDs derived from chlorhexidine gluconate into three groups with uniformly small-scale, middle-scale, and large-scale particle sizes by using different molecular weight cut-off membranes. These positively charged particles exhibit significant antibacterial activity against the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus aureus; they can cause an increase in bacterial cell permeability, synergistic destabilization, and broken integrity of the plasma membrane. Impressively, we found that antibacterial activity increases as the size of the CDs decreases. This phenomenon may stem from the differences in cellular uptake and distribution of CDs in the plasma membrane or restriction between the polar functional group and DNA molecule. Our study of the size effect as a target may improve the understanding of killing microorganisms by antibacterial CD drugs.

Specific Anti-biofilm Activity of Carbon Quantum Dots by Destroying P. gingivalis Biofilm Related Genes

Introduction

Biofilms protect bacteria from antibiotics and this can produce drug-resistant strains, especially the main pathogen of periodontitis, Porphyromonas gingivalis. Carbon quantum dots with various biomedical properties are considered to have great application potential in antibacterial and anti-biofilm treatment.

Methods

Tinidazole carbon quantum dots (TCDs) and metronidazole carbon quantum dots (MCDs) were prepared by a hydrothermal method with the clinical antibacterial drugs tinidazole and metronidazole, respectively. Then, TCDs and MCDs were characterized by transmission electron microscopy, UV–visible spectroscopy, infrared spectroscopy and energy-dispersive spectrometry. The antibacterial effects were also investigated under different conditions.

Results

The TCDs and MCDs had uniform sizes. The results of UV–visible and energy-dispersive spectrometry confirmed their important carbon polymerization structures and the activity of the nitro group, which had an evident inhibitory effect on P. gingivalis, but almost no effect on other bacteria, including Escherichia coli, Staphylococcus aureus and Prevotella nigrescens. Importantly, the TCDs could penetrate the biofilms to further effectively inhibit the growth of P. gingivalis under the biofilms. Furthermore, it was found that the antibacterial effect of TCDs lies in its ability to impair toxicity by inhibiting the major virulence factors and related genes involved in the biofilm formation of P. gingivalis, thus affecting the self-assembly of biofilm-related proteins.

Conclusion

The findings demonstrate a promising new method for improving the efficiency of periodontitis treatment by penetrating the P. gingivalis biofilm with preparations of nano-level antibacterial drugs.

A cost-effective combination of Rose Bengal and off-the-shelf cationic polystyrene for the photodynamic inactivation of Pseudomonas aeruginosa

Two new photoactive materials have been prepared, characterized and tested against Pseudomonas aeruginosa bacteria (planktonic suspension). The synthesis of the polymeric photosensitizers can be made at a multigram scale, in few minutes, starting from inexpensive and readily available materials, such as Rose Bengal (photosensitizer) and ion exchange resins Amberlite® IRA 900 (macroporous) or IRA 400 (gel-type) as cationic polystyrene supports. The most notable feature of these systems is their notable bactericidal activity in the dark (4-5 log₁₀ CFU/mL reduction of the population of P. aeruginosa) which becomes enhanced upon irradiation with visible light (to reach a total reduction of 8 log₁₀ CFU/mL for the macroporous polymer at a fluence of 120 J/cm² using green light of 515 nm).