The Photochemical Degradation of Bacterial Cell Wall Using Penicillin-Based Carbon Dots: Weapons Against Multi-Drug Resistant (MDR) Strains

Poly(Lysine)-Derived Carbon Quantum Dots Conquer Enterococcus faecalis Biofilm-Induced Persistent Endodontic Infections

Introduction

Persistent endodontic infections (PEIs) mediated by bacterial biofilm mainly cause persistent periapical inflammation, resulting in recurrent periapical abscesses and progressive bone destruction. However, conventional root canal disinfectants are highly damaging to the tooth and periodontal tissue and ineffective in treating persistent root canal infections. Antimicrobial materials that are biocompatible with apical tissues and can eliminate PEIs-associated bacteria are urgently needed.

Methods

Here, ε-poly (L-lysine) derived carbon quantum dots (PL-CQDs) are fabricated using pyrolysis to remove PEIs-associated bacterial biofilms.

Results

Due to their ultra-small size, high positive charge, and active reactive oxygen species (ROS) generation capacity, PL-CQDs exhibit highly effective antibacterial activity against Enterococcus faecalis (E. faecalis), which is greatly dependent on PL-CQDs concentrations. 100 µg/mL PL-CQDs could kill E. faecalis in 5 min. Importantly, PL-CQDs effectively achieved a reduction of biofilms in the isolated teeth model, disrupting the dense structure of biofilms. PL-CQDs have acceptable cytocompatibility and hemocompatibility in vitro and good biosafety in vivo.

Discussion

Thus, PL-CQDs provide a new strategy for treating E. faecalis-associated PEIs.

Carbon Dot Based Carbon Nanoparticles as Potent Antimicrobial, Antiviral, and Anticancer Agents

Antimicrobial and anticancer drugs are widely used due to increasing widespread infectious diseases caused by microorganisms such as bacterial, fungal, viral agents, or cancer cells, which are one of the major causes of mortality globally. Nevertheless, several microorganisms developed resistance to antibiotics as a result of genetic changes that have occurred over an extended period. Carbon-based materials, particularly carbon dots (C-dots), are potential candidates for antibacterial and anticancer nanomaterials due to their low toxicity, ease of synthesis and functionalization, high dispersibility in aqueous conditions, and promising biocompatibility. In this Review, the content is divided into four sections. The first section concentrates on C-dot structures, surface functionalization, and morphology. Following that, we summarize C-dot classifications and preparation methods such as arc discharge, laser ablation, electrochemical oxidation, and so on. The antimicrobial applications of C-dots as antibacterial, antifungal, and antiviral agents both in vivo and in vitro are discussed. Finally, we thoroughly examined the anticancer activity displayed by C-dots.

Biogenic carbon dots: a novel mechanistic approach to combat multidrug-resistant critical pathogens on the global priority list

This study delves into investigating alternative methodologies for anti-microbial therapy by focusing on the mechanistic assessment of carbon dots (CDs) synthesized from F. benghalensis L. extracts. These biogenic CDs have shown remarkable broad-spectrum anti-bacterial activity even against multi-drug resistant (MDR) bacterial strains, prompting a deeper examination of their potential as novel anti-microbial agents. The study highlights the significant detrimental impact of CDs on bacterial cells through oxidative damage, which disrupts the delicate balance of ROS control within the cells. Notably, even at low doses, the anti-bacterial activity of CDs against MDR strains of P. aeruginosa and E. cloacae is highly effective, demonstrating their promise as potent antimicrobial agents. The research sheds light on the capacity of CDs to generate ROS, leading to membrane lipid peroxidation, loss of membrane potential, and rupture of bacterial cell membranes, resulting in cytoplasmic leakage. SEM and TEM analysis revealed time-dependent cell surface, morphological, and ultrastructural changes such as elongation of the cells, irregular surface protrusion, cell wall and cell membrane disintegration, internalization, and aggregations of CDs. These mechanisms offer a comprehensive explanation of how CDs exert their anti-bacterial effects. We also determined the status of plasma membrane integrity and evaluated live (viable) and dead cells upon CD exposure by flow cytometry. Furthermore, comet assay, biochemical assays, and SDS PAGE identify DNA damage, carbohydrate and protein leakage, and distinct differences in protein expression, adding another layer of understanding to the mechanisms behind CDs' anti-bacterial activity. These findings pave the way for future research on managing ROS levels and developing CDs with enhanced anti-bacterial properties, presenting a breakthrough in anti-microbial therapy.

Recent progress in carbon dots for anti-pathogen applications in oral cavity

Background

Oral microbial infections are one of the most common diseases. Their progress not only results in the irreversible destruction of teeth and other oral tissues but also closely links to oral cancers and systemic diseases. However, traditional treatment against oral infections by antibiotics is not effective enough due to microbial resistance and drug blocking by oral biofilms, along with the passive dilution of the drug on the infection site in the oral environment.

Aim of review

Besides the traditional antibiotic treatment, carbon dots (CDs) recently became an emerging antimicrobial and microbial imaging agent because of their excellent (bio)physicochemical performance. Their application in treating oral infections has received widespread attention, as witnessed by increasing publication in this field. However, to date, there is no comprehensive review available yet to analyze their effectiveness and mechanism. Herein, as a step toward addressing the present gap, this review aims to discuss the recent advances in CDs against diverse oral pathogens and thus propose novel strategies in the treatment of oral microbial infections.

Key scientific concepts of review

In this manuscript, the recent progress of CDs against oral pathogens is summarized for the first time. We highlighted the antimicrobial abilities of CDs in terms of oral planktonic bacteria, intracellular bacteria, oral pathogenic biofilms, and fungi. Next, we introduced their microbial imaging and detection capabilities and proposed the prospects of CDs in early diagnosis of oral infection and pathogen microbiological examination. Lastly, we discussed the perspectives on clinical transformation and the current limitations of CDs in the treatment of oral microbial 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.

Facile synthesis of multifunctional pharmaceutical carbon dots for targeted bioimaging and chemotherapy of tumors

Drug-derived carbon dots (CDs) not only have excellent photoluminescence properties of CDs, but also maintain pharmacological effects of original drugs, so as to realize extended applications for both bioimaging and chemotherapy. In this work, metformin (Met)-derived CDs (Met-CDs) as multifunctional nanocarriers with tumor cell imaging and cancer therapy are synthesized using Met and citric acid as precursors. The created Met-CDs exhibit obvious resistance to photobleaching, significant pH sensitivity in acidic environments, good pH stability in alkaline environments, and high temperature sensitivity. In addition, we further investigate the biological activity of Met-CDs using diabetic cell models, which demonstrate the ability of Met-CDs to treat diabetes and reduce the production of reactive oxygen species in diseased cells. Subsequently, human alveolar adenocarcinoma basal epithelial cells (A549) are cultured in both normal glucose and low glucose media, and different concentrations of Met and Met-CDs are added to investigate the effect of Met-CDs on A549 cells. Finally, we successfully utilize the prepared Met-CDs to image live A549 cells in vitro in normal glucose medium. The Met-CDs prepared in this work reveal high potential to be used as both fluorescent probes and drug agents for tumor therapy, realizing controllable integrated diagnosis and treatment of diseases.

Carbon dot-based therapeutics for combating drug-resistant bacteria and biofilm infections in food preservation

Drug-resistant bacteria are caused by antibiotic abuse and/or biofilm formation and have become a threat to the food industry. Carbon dot (CD)-based nanomaterials are a very promising tools for combating pathogenic and spoilage bacteria, and they possess exceptional and adjustable photoelectric and chemical properties. In view of the rapid development of CD-based nanomaterials and their increasing popularity in the food industry, a comprehensive and updated review is needed to summarize their antimicrobial mechanisms and applications in foods. This review discusses the synthesis of CDs, antimicrobial mechanisms, and their applications for extending the shelf life of food. It includes the synthesis of CDs using small molecules, polymers, and biomass. It also discusses the different antimicrobial mechanisms of CDs and their use as antibacterial agents and carriers/ligands. CD-based materials have proven effective against pathogenic and spoilage bacteria in food by inhibiting planktonic bacteria and biofilms. Optimization of the production parameters of CDs can help them achieve a full-spectral response, but degradability still requires further research.

Fucoidan-derived carbon dots against Enterococcus faecalis biofilm and infected dentinal tubules for the treatment of persistent endodontic infections

Enterococcus faecalis (E. faecalis) biofilm-associated persistent endodontic infections (PEIs) are one of the most common tooth lesions, causing chronic periapical periodontitis, root resorption, and even tooth loss. Clinical root canal disinfectants have the risk of damaging soft tissues (e.g., mucosa and tongue) and teeth in the oral cavity, unsatisfactory to the therapy of PEIs. Nanomaterials with remarkable antibacterial properties and good biocompatibility have been developed as a promising strategy for removing pathogenic bacteria and related biofilm. Herein, carbon dots (CDs) derived from fucoidan (FD) are prepared through a one-pot hydrothermal method for the treatment of PEIs. The prepared FDCDs (7.15 nm) with sulfate groups and fluorescence property are well dispersed and stable in water. Further, it is found that in vitro FDCDs display excellent inhibiting effects on E. faecalis and its biofilm by inducing the formation of intracellular and extracellular reactive oxygen species and altering bacterial permeability. Importantly, the FDCDs penetrated the root canals and dentinal tubules, removing located E. faecalis biofilm. Moreover, the cellular assays show that the developed FDCDs have satisfactory cytocompatibility and promote macrophage recruitment. Thus, the developed FDCDs hold great potential for the management of PEIs.

Photodynamic Anti-Bacteria by Carbon Dots and Their Nano-Composites

The misuse of many types of broad-spectrum antibiotics leads to increased antimicrobial resistance. As a result, the development of a novel antibacterial agent is essential. Photodynamic antimicrobial chemotherapy (PACT) is becoming more popular due to its advantages in eliminating drug-resistant strains and providing broad-spectrum antibacterial resistance. Carbon dots (CDs), zero-dimensional nanomaterials with diameters smaller than 10 nm, offer a green and cost-effective alternative to PACT photosensitizers. This article reviewed the synthesis methods of antibacterial CDs as well as the recent progress of CDs and their nanocomposites in photodynamic sterilization, focusing on maximizing the bactericidal impact of CDs photosensitizers. This review establishes the base for future CDs development in the PACT field.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Highly fluorescent carbon dots as novel theranostic agents for biomedical applications

As an emerging fluorescent nanomaterial, carbon dots (CDs) exhibit many attractive physicochemical features, including excellent photoluminescence properties, good biocompatibility, low toxicity and the ability to maintain the unique properties of the raw material. Therefore, CDs have been intensively pursued for a wide range of applications, such as bioimaging, drug delivery, biosensors and antibacterial agents. In this review, we systematically summarize the synthesis methods of these CDs, their photoluminescence mechanisms, and the approaches for enhancing their fluorescence properties. Particularly, we summarize the recent research on the synthesis of CDs from drug molecules as raw materials and introduce the representative application aspects of these fascinating CDs. Finally, we look into the future direction of CDs in the biomedical field and discuss the challenges encountered in the current development.

Microbial inhibition and biosensing with multifunctional carbon dots: Progress and perspectives

Carbon dots (CDs) and their doped counterparts including nitrogen-doped CDs (N@CDs) have been synthesized by bottom-up or top-down approaches from different precursors. The attractiveness of such emerging 2D‑carbon-based nanosized materials is attributed to their excellent biocompatibility, preparation, aqueous dispersibility, and functionality. The antimicrobial, optical, and electrochemical properties of CDs have been advocated for two important biotechnological applications: bacterial eradication and sensing/biosensing. CDs as well as N@CDs act as antimicrobial agents as their surfaces encompass functional hydroxyl, carboxyl, and amino groups that generate free radicals. As a new class of photoluminescent nanomaterials, CDs can be employed in diversified analytics. CDs with surface carboxyl or amino groups form nanocomposites with nanomaterials or be conjugated with biorecognition molecules toward the development of sensors/biosensors. The deployment of conductive CDs in electrochemical sensing has also increased significantly because of their quantum size, excellent biocompatibility, enzyme-mimicking activity, and high surface area. The review also addresses the ongoing challenges and promises of CDs in pathogenesis and analytics. Perspectives on the future possibilities include the use of CDs in microbial viability assay, wound healing, antiviral therapy, and medical devices.

Green Synthesis of Silver Nanoparticles by Extracellular Extracts from Aspergillus japonicus PJ01

The present study focuses on the biological synthesis, characterization, and antibacterial activities of silver nanoparticles (AgNPs) using extracellular extracts of Aspergillus japonicus PJ01.The optimal conditions of the synthesis process were: 10 mL of extracellular extracts, 1 mL of AgNO3 (0.8 mol/L), 4 mL of NaOH solution (1.5 mol/L), 30 °C, and a reaction time of 1 min. The characterizations of AgNPs were tested by UV-visible spectrophotometry, zeta potential, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric (TG) analyses. Fourier transform infrared spectroscopy (FTIR) analysis showed that Ag+ was reduced by the extracellular extracts, which consisted chiefly of soluble proteins and reducing sugars. In this work, AgNO3 concentration played an important role in the physicochemical properties and antibacterial properties of AgNPs. Under the AgNO3 concentration of 0.2 and 0.8 mol/L, the diameters of AgNPs were 3.8 ± 1.1 and 9.1 ± 2.9 nm, respectively. In addition, smaller-sized AgNPs showed higher antimicrobial properties, and the minimum inhibitory concentration (MIC) values against both E. coli and S. aureus were 0.32 mg/mL.

One-Pot Microwave-Assisted Synthesis of Carbon Dots and in vivo and in vitro Antimicrobial Photodynamic Applications

Carbon-based photosensitizers are more attractive than the other ones based on their low cost, high stability, broadband of light absorption, tunable emission spectra, high quantum yield, water solubility, high resistance to metabolic degradation, and selective delivery. These properties allow multiple applications in the field of biology and medicine. The present study evaluated in vitro and in vivo the antimicrobial photodynamic effect of a one-pot microwave produced C-DOTS based on citric acid. The in vitro assays assessed the effectiveness of illuminated C-DOTS (C-DOTS + light) against Staphylococcus aureus suspension and biofilm. The concentrations of 6.9 and 13.8 mg/mL of C-DOTS and light doses of 20 and 40 J/cm2 were able to reduce significantly the microorganisms. Based on these parameters and results, the in vivo experiments were conducted in mice, evaluating this treatment on wounds contaminated with S. aureus. The viability test showed that C-DOTS-mediated photodynamic inactivation reduced 104 log of the bacteria present on the skin lesions. These results, altogether, showed that antibacterial photodynamic therapy using C-DOTS is a promising and viable treatment for Gram-positive bacteria-infected wounds.

One-step synthesis of blue-green luminescent carbon dots by a low-temperature rapid method and their high-performance antibacterial effect and bacterial imaging

Due to the global infection problem caused by the abuse of antibiotics, the preparation of novel antibacterial nanomaterials is a key and basic requirement for applications in antibacterial and bacterial imaging fields. This paper reports the one-step preparation of blue-green-emitting carbon dots (CDs) under low temperature (80 °C) with glucose as the carbon source, citric acid as the dehydrating agent, and polyethyleneimine as the nitrogen source. Through inhibition zone tests and minimum inhibitory concentration (MIC) experiments, the inhibitory abilities of prepared CDs against various microorganisms, including gram-positive bacteria, gram-negative bacteria and fungi, were compared. It is worth mentioning that the MIC of CDs against Staphylococcus aureus reaches 4.7 μg ml^-1, and the CDs exhibit excellent biocompatibility. Moreover, studies on visual-treatment therapy, in which infection treatment can be performed at the same time as bacterial imaging, with the prepared functional antibacterial CDs based on fluorescence confocal imaging would be beneficial to their promising future in medical and biological fields.

Antimicrobial carbon nanodots: photodynamic inactivation and dark antimicrobial effects on bacteria by brominated carbon nanodots

The evolving threat of antibiotic resistance development in pathogenic bacteria necessitates the continued cultivation of new technologies and agents to mitigate associated negative health impacts globally. It is no surprise that infection prevention and control are cited by the Centers for Disease Control and Prevention (CDC) as two routes for combating this dangerous trend. One technology that has gained great research interest is antimicrobial photodynamic inactivation of bacteria, or APDI. This technique permits controllable activation of antimicrobial effects by combining specific light excitation with the photodynamic properties of a photosensitizer; when activated, the photosensitizer generates reactive oxygen species (ROS) from molecular oxygen via either a type I (electron transfer) or type II (energy transfer) pathway. These species subsequently inflict oxidative damage on nearby bacteria, resulting in suppressed growth and cell death. To date, small molecule photosensitizers have been developed, yet the scalability of these as widespread sterilization agents is limited due to complex and costly synthetic procedures. Herein we report the use of brominated carbon nanodots (BrCND) as new photosensitizers for APDI. These combustion byproducts are easily and inexpensively collected; incorporation of bromine into the nanodot permits photosensitization effects that are not inherent to the carbon nanodot structure alone-a consequence of triplet character gained by the heavy atom effect. BrCND demonstrate both type I and type II photosensitization under UV-A irradiation, and furthermore are shown to have significant antimicrobial effects against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and Listeria monocytogenes as well. A mechanism of "dark" toxicity is additionally reported; the pH-triggered release of reactive nitrogen species is detected from a carbon nanodot structure for the first time. The results described present the BrCND structure as a competitive new antimicrobial agent for controllable sterilization of bacteria.

Anti-pathogenic activity of graphene nanomaterials: A review

Graphene and its derivatives are promising candidates for a variety of biological applications, among which, their anti-pathogenic properties are highly attractive due to the outstanding physicochemical characteristics of these novel nanomaterials. The antibacterial, antiviral and antifungal performances of graphene are increasingly becoming more important due to the pathogen's resistance to existing drugs. Despite this, the factors influencing the antibacterial activity of graphene nanomaterials, and consequently, the mechanisms involved are still controversial. This review aims to systematically summarize the literature, discussing various factors that affect the antibacterial performance of graphene materials, including the shape, size, functional group and the electrical conductivity of graphene flakes, as well as the concentration, contact time and the pH value of the graphene suspensions used in related microbial tests. We discuss the possible surface and edge interactions between bacterial cells and graphene nanomaterials, which cause antibacterial effects such as membrane/oxidative/photothermal stresses, charge transfer, entrapment and self-killing phenomena. This article reviews the anti-pathogenic activity of graphene nanomaterials, comprising their antibacterial, antiviral, antifungal and biofilm-forming performance, with an emphasis on the antibacterial mechanisms involved.

Design of Photosensitizing Agents for Targeted Antimicrobial Photodynamic Therapy

Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O2-, type-I mechanism) or singlet oxygen (1O2*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT.

Carbon Nanodots in Photodynamic Antimicrobial Therapy: A Review

Antibiotic resistance development in bacteria is an ever-increasing global health concern as new resistant strains and/or resistance mechanisms emerge each day, out-pacing the discovery of novel antibiotics. Increasingly, research focuses on alternate techniques, such as antimicrobial photodynamic therapy (APDT) or photocatalytic disinfection, to combat pathogens even before infection occurs. Small molecule "photosensitizers" have been developed to date for this application, using light energy to inflict damage and death on nearby pathogens via the generation of reactive oxygen species (ROS). These molecular agents are frequently limited in widespread application by synthetic expense and complexity. Carbon dots, or fluorescent, quasi-spherical nanoparticle structures, provide an inexpensive and "green" solution for a new class of APDT photosensitizers. To date, reviews have examined the overall antimicrobial properties of carbon dot structures. Herein we provide a focused review on the recent progress for carbon nanodots in photodynamic disinfection, highlighting select studies of carbon dots as intrinsic photosensitizers, structural tuning strategies for optimization, and their use in hybrid disinfection systems and materials. Limitations and challenges are also discussed, and contemporary experimental strategies presented. This review provides a focused foundation for which APDT using carbon dots may be expanded in future research, ultimately on a global scale.

Enhanced bacterial killing by vancomycin in staphylococcal biofilms disrupted by novel, DMMA-modified carbon dots depends on EPS production

Alternatives for less and less effective antibiotic treatment of bacterial infections, are amongst others based on nanotechnological innovations, like carbon-dots. However, with a focus on chemistry, important characteristics of bacterial strains, like (in-)ability to produce extracellular-polymeric-substances (EPS) are often neglected. EPS is the glue that certain bacterial strains produce to keep a biofilm together. Here we report on synthesis of novel, pH-responsive, 2,3-dimethylmaleic-anhydride modified carbon-dots (C_DMMA-dots). C_DMMA-dots, like unmodified C-dots without DMMA, were little bactericidal. However, C_DMMA-dots reduced volumetric-bacterial-density within the acidic-environment of a biofilm for a non-EPS-producing Staphylococcus epidermidis strain, indicative for a more open structure. Such a structural disruption was not observed for an EPS-producing strain. Disrupted biofilms of the non-EPS-producing strain pre-exposed to C_DMMA-dots at pH 5.0, were more amenable to vancomycin penetration and killing of their inhabitants than biofilms of EPS-producing-staphylococci. Herewith, we describe a new role of carbon-dots as synthetic disruptants of biofilm structure. It is a partial success story, identifying the challenge of making carbon-dots that act as a universal disruptant for biofilms of strains with different microbiological characteristics, most notably the ability to produce or not-produce EPS. Such carbon-dots, will enable more effective clinical treatment of bacterial infections combined with current antibiotics.

Ionic Liquid-Functionalized Multiwalled Carbon Nanotube-Based Hydrophobic Coatings for Robust Antibacterial Applications

In recent years, the biomimetic superhydrophobic coatings have received tremendous attention, owing to their potential in fabricating self-cleaning surfaces, in environmental applications. Consequently, extensive research has been devoted to create a superhydrophobic surface using the oxidized derivatives of CNTs and graphene. Thus, the design and development of a self-cleaning/superhydrophobic surface with good biocompatibility are an effective approach to deal with the bacterial infections related to biomedical devices used in hospitals. In this context, herein, we have developed the material based on ionic liquid (IL)-functionalized multiwalled carbon nanotubes (MWCNTs) for hydrophobic coatings, which was fully characterized with various techniques such as Fourier transform infrared, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. We have evaluated the synthesized ILs for their antibacterial potential against the pathogenic bacterial strains such as Gram-positive (Staphylococcus aureus and methicillin-resistant S. aureus) and Gram-negative (Escherichia coli) bacterial strains. Further, atomic force and scanning electron microscopic studies have been performed to investigate the morphological changes to unravel the mechanism of action, whereas DNA binding study indicates the binding of IL-1d@MWCNT with DNA (K_a = 2.390 × 10⁴ M^-1). Furthermore, the developed material (IL-1d@MWCNT) is coated onto the surface of polyvinyl chloride (PVC) and evaluated for hydrophobicity through water contact angle measurements and possesses long-term antibacterial efficiency against both under-investigating pathogenic strains. For the biocompatibility assay, the obtained coated PVC material has also been evaluated for its cytotoxicity, and results reveal no toxicity against viable cells. These all results are taken together, indicating that by coating with the developed material IL-1d@MWCNT, a robust self-sterilizing surface has achieved, which helps in maintaining a bacteria-free surface.

Light-activated nanozymes: catalytic mechanisms and applications

Recently, nanozymes have attracted enormous interest for their high stability, low cost and various enzyme-like activities. In nature, many biochemical reactions require light. Recently, introducing light to nanozymes has also been reported, especially for photosensitized oxygen activation. Compared to normal nanozymes, light-activated nanozymes possess several advantages including light-regulated activity, using molecular oxygen as a green oxidant, and often higher activity can be achieved. Herein, we summarize light-activated nanozymes, starting from their photophysical processes and identification of reactive oxygen species (ROS). Although the types of light-activated nanozymes are still quite limited and cannot yet mimic the same reactions as natural photo-related enzymes, they have widened the range of nanozymes. A few specific applications are highlighted, including sensing, chemical synthesis, degradation of organic pollutants, and cleavage and repair of DNA. Finally, a few future research opportunities are discussed.

Investigation of the antibacterial activity of Ag-NPs conjugated with a specific antibody against Staphylococcus aureus after photoactivation

AIM

This work reports a new method for the use of lasers for the selective killing of bacteria targeted using light-absorbing Silver nanoparticles (Ag-NPs) conjugated with a specific antibody against the Gram-positive bacterium Staphylococcus aureus (S. aureus).

METHODS AND RESULTS

Ag-NPs were synthesized using a chemical reduction method and characterized with respect to their surface plasmon resonance, surface morphology via transmission electron microscopy (TEM) and dynamic light scattering (DLS). The bacterial surface was targeted using 20 nm Ag-NPs conjugated with an anti-protein A antibody. Labelled bacteria were irradiated with blue visible laser at 2·04 W/cm² . The antibacterial activity of functionalized Ag-NPs was investigated by fluorescence microscopy after irradiation, and morphological changes in S. aureus after laser treatment were assessed using scanning electron microscopy (SEM). The laser-irradiated, functionalized Ag-NPs exhibited significant bactericidal activity, and laser-induced bacterial damage was observed after 10 min of laser irradiation against S. aureus. The fluorescence microscopic analysis results supported that bacterial cell death occurred in the presence of the functionalized Ag-NPs.

CONCLUSIONS

The results of this study suggest that a novel method for the preparation of functionalized nanoparticles has potential as a potent antibacterial agent for the selective killing of resistant disease-causing bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that Ag-NPs functionalized with a specific antibody, could be used in combination with laser radiation as a novel treatment to target resistant bacterial and fungal pathogens with minimal impact on normal microflora.

Anticancer SAR establishment and novel accruing signal transduction model of drug action using biscoumarin scaffold

In this paper, we have established methylenebis (4-hydroxy-2H-chromen-2-one) as a promising anticancer scaffold with kinesin spindle protein (KSP) inhibitory activity under malignant condition. A series of biscoumarin derivatives (MN1 to MN30) with different substituent were synthesized, and their anticancer activity was explored. Six biscoumarin derivatives that were found active were further selected to formulate organic nanoparticles (ONPs). Anticancer activity of both the forms (viz conventional and ONPs) was compared. MN30 was found most potent whereby MN10 showed good anticancer activity in both, i.e., conventional and ONP form; the structural activity relationship (SAR) study has been established. Computational investigation revealed biscoumarin scaffold as a suitable pharmacophore to bind against KSP protein. Molecular dynamics simulation studies revealed protein-ligand stability and dynamic behavior of biscoumarin-KSP complex. Finally, accruing signal transduction model was formulated to explain the observed MTT trend of conventional and ONP form. The model seems useful towards solving population specific varied results of chemotherapeutic agents. According to the model, MN10 and MN30 derivatives have good pharmacodynamics inertia and therefore, both the molecules were able to provide dose-dependent cytotoxic results.

Carbon Dots for Sensing and Killing Microorganisms

Carbon dots (or carbon quantum dots) are small (less than 10 nm) and luminescent carbon nanoparticles with some form of surface passivation. As an emerging class of nanomaterials, carbon dots have found wide applications in medicine, bioimaging, sensing, electronic devices, and catalysis. In this review, we focus on the recent advancements of carbon dots for sensing and killing microorganisms, including bacteria, fungi, and viruses. Synthesis, functionalization, and a toxicity profile of these carbon dots are presented. We also discuss the underlying mechanisms of carbon dot-based sensing and killing of microorganisms.

Solar-excited graphene quantum dots for bacterial inactivation via generation of reactive oxygen species

Nanoscale photocatalysts have attracted abundant research attention in the solar-activated disinfection. In this work, we find that solar irradiation significantly improves the antimicrobial activity of graphene quantum dots (GQDs), accompanied by severe oxidative stress and membrane damage. By using electron spin resonance (ESR) technique, we confirm that different reactive oxygen species (ROS), including singlet oxygen (¹O₂), hydroxyl radical (•OH), and superoxide anion (O₂^•-) were generated by GQDs upon irradiation with simulated sunlight. Additionally, these generated ROS will further facilitate lipid peroxidation of cell membrane and suppress bacterial antioxidant systems, enhancing the phototoxicity of GQDs. These findings will bring major advancements of GQDs in applications of solar-driven bacterial disinfection.

Design of dual drug-loaded dendrimer/carbon dot nanohybrids for fluorescence imaging and enhanced chemotherapy of cancer cells

Dual drug-loaded dendrimer/CD nanohybrids can be developed for fluorescence imaging and enhanced chemotherapy of cancer cells.

Phosphorescent Carbon Dots for Highly Efficient Oxygen Photosensitization and as Photo-oxidative Nanozymes

Materials for photosensitized oxygen activation are extremely important for a suite of photodynamic applications in biomedical, analytical, and energy sectors. Carbon-based photosensitizers are attractive for their low cost and high stability, but most of them such as fullerene and graphene quantum dots suffer from low efficiency, and the rational design of carbon-based photosensitizers remains a challenge. Given the similar chemical origin of phosphorescence and photosensitization, we herein synthesized a series of nitrogen-doped carbon dots (C-dots) and confirmed that their photo-oxidation activity correlated with their phosphorescence quantum yields, providing a direction for the rational designing of such materials. Compared to other carbon nanomaterials and molecular photosensitizers, these C-dots have the highest activity, and they can finish oxidation reactions in a few seconds. The excellent photosensitized oxygen activation makes these water-soluble C-dots a promising oxidase-mimicking nanozyme for photodynamic antimicrobial chemotherapy and other applications.