Bovine Serum Albumin Amplified Reactive Oxygen Species Generation from Anthrarufin-Derived Carbon Dot and Concomitant Nanoassembly for Combination Antibiotic-Photodynamic Therapy Application

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.

Multifunctional Self-Healing Carbon Dot-Gelatin Bioadhesive: Improved Tissue Adhesion with Simultaneous Drug Delivery, Optical Tracking, and Photoactivated Sterilization

Bioadhesives with all-inclusive properties for simultaneous strong and robust adhesion, cohesion, tracking, drug delivery, self-sterilization, and nontoxicity are still farfetched. Herein, a carbon dot (CD) is made to infuse each of the above-desired aspects with gelatin, an inexpensive edible protein. The CD derived through controlled hydrothermal pyrolysis of dopamine and terephthaldehyde retained -NH2, -OH, -COOH, and, most importantly, -CHO functionality on the CD surface for efficient skin adhesion and cross-linking. Facile fabrication of CD-gelatin bioadhesive through covalent conjugation of -CHO of the CD with -NH2 of gelatin through Schiff base formation was accomplished. This imparts remarkable self-healing attributes as well as excellent adhesion and cohesion evident from physicomechanical analysis in a porcine skin model. Improved porosity of the bioadhesive allows loading hemin as a model drug whose disembarkment is tracked with intrinsic CD photoluminescence. In a significant achievement, antibiotic-free self-sterilization of bioadhesive is demonstrated through visible light (white LED, 23 W)-irradiated photosensitization of the CD to produce reactive oxygen species for annihilation of both Gram-positive and Gram-negative bacteria with exceptional efficacy (99.9%). Thus, a comprehensive CD-gelatin bioadhesive for superficial and localized wound management is reported as a promising step for the transformation of the bioadhesive domain through controlled nanotization for futuristic clinical translations.

Functional nanomaterials as photosensitizers or delivery systems for antibacterial photodynamic therapy

Bacterial infection is a global health problem that closely related to various diseases threatening human life. Although antibiotic therapy has been the mainstream treatment method for various bacterial infectious diseases for decades, the increasing emergence of bacterial drug resistance has brought enormous challenges to the application of antibiotics. Therefore, developing novel antibacterial strategies is of great importance. By producing reactive oxygen species (ROS) with photosensitizers (PSs) under light irradiation, antibacterial photodynamic therapy (aPDT) has emerged as a non-invasive and promising approach for treating bacterial infections without causing drug resistance. However, the insufficient therapeutic penetration, poor hydrophilicity, and poor biocompatibility of traditional PSs greatly limit the efficacy of aPDT. Recently, studies have found that nanomaterials with characteristics of favorable photocatalytic activity, surface plasmonic resonance, easy modification, and high drug loading capacity can improve the therapeutic efficacy of aPDT. In this review, we aim to provide a comprehensive understanding of the mechanism of nanomaterials-mediated aPDT and summarize the representative nanomaterials in aPDT, either as PSs or carriers for PSs. In addition, the combination of advanced nanomaterials-mediated aPDT with other therapies, including targeted therapy, gas therapy, and multidrug resistance (MDR) therapy, is reviewed. Also, the concerns and possible solutions of nanomaterials-based aPDT are discussed. Overall, this review may provide theoretical basis and inspiration for the development of nanomaterials-based aPDT.

Quantum dots as advanced nanomaterials for food quality and safety applications: A comprehensive review and future perspectives

The importance of food quality and safety lies in ensuring the best product quality to meet consumer demands and public health. Advanced technologies play a crucial role in minimizing the risk of foodborne illnesses, contamination, drug residue, and other potential hazards in food. Significant materials and technological advancements have been made throughout the food supply chain. Among them, quantum dots (QDs), as a class of advanced nanomaterials with unique physicochemical properties, are progressively demonstrating their value in the field of food quality and safety. This review aims to explore cutting-edge research on the different applications of QDs in food quality and safety, including encapsulation of bioactive compounds, detection of food analytes, food preservation and packaging, and intelligent food freshness indicators. Moreover, the modification strategies and potential toxicities of diverse QDs are outlined, which can affect performance and hinder applications in the food industry. The findings suggested that QDs are mainly used in analyte detection and active/intelligent food packaging. Various food analytes can be detected using QD-based sensors, including heavy metal ions, pesticides, antibiotics, microorganisms, additives, and functional components. Moreover, QD incorporation aided in improving the antibacterial and antioxidant activities of film/coatings, resulting in extended shelf life for packaged food. Finally, the perspectives and critical challenges for the productivity, toxicity, and practical application of QDs are also summarized. By consolidating these essential aspects into this review, the way for developing high-performance QD-based nanomaterials is presented for researchers and food technologists to better capitalize upon this technology in food applications.

Coal waste-derived synthesis of yellow oxidized graphene quantum dots with highly specific superoxide dismutase activity: characterization, kinetics, and biological studies

The disintegration of coal-based precursors for the scalable production of nanozymes relies on the fate of solvothermal pyrolysis. Herein, we report a novel economic and scalable strategy to fabricate yellow luminescent graphene quantum dots (YGQDs) by remediating unburnt coal waste (CW). The YGQDs (size: 7-8 nm; M.W: 3157.9 Da) were produced using in situ "anion-radical" assisted bond cleavage in water (within 8 h; at 121 °C) with yields of ∼87%. The presence of exposed surface and edge groups, such as COOH, C-O-C, and O-H, as structural defects accounted for its high fluorescence with εmax ∼530 nm at pH 7. Besides, these defects also acted as radical stabilizers, demonstrating prominent anti-oxidative activity of ∼4.5-fold higher than standard ascorbic acid (AA). In addition, the YGQDs showed high biocompatibility towards mammalian cells, with 500 μM of treatment dose showing <15% cell death. The YGQDs demonstrated specific superoxide dismutase (SOD) activity wherein 15 μM YGQDs equalled the activity of 1-unit biological SOD (bSOD), measured using the pyrogallol assay. The Km for YGQDs was ∼10-fold higher than that for bSOD. However, the YGQDs retained their SOD activity in harsh conditions like high temperatures or denaturing reactions, where the activity of bSOD is completely lost. The binding affinity of YGQDs for superoxide ions, measured from isothermal calorimetry (ITC) studies, was only 10-fold lower than that of bSOD (Kd of 586 nM vs. 57.3 nM). Further, the pre-treatment of YGQDs (∼10-25 μM) increased the cell survivability to >75-90% in three cell lines during ROS-mediated cell death, with the highest survivability being shown for C6-cells. Next, the ROS-induced apoptosis in C6-cells (model for neurodegenerative diseases study), wherein YGQDs uptake was confirmed by confocal microscopy, showed ∼5-fold apoptosis alleviation with only 5 μM pretreatment. The YGQDs also restored the expression of pro-inflammatory Th1 cytokines (TNF-α, IFN-γ, IL-6) and anti-inflammatory Th2 cytokines (IL-10) to their basal levels, with a net >3-fold change observed. This further explains the molecular mechanism for the antioxidant property of YGQDs. The high specific SOD activity associated with YGQDs may provide the cheapest alternative source for producing large-scale SOD-based nanozymes that can treat various oxidative stress-linked disorders/diseases.

Carbonized Tetracycline: a new class of nanomaterial with tuneable antioxidant, reduced cytotoxicity, immunomodulatory, and osteogenic properties

Tetracycline (TET), a broad-spectrum antibiotic, also possesses different non-antibiotic activities such as inhibition of metalloproteinase (MMP), anti-inflammatory, antioxidant, high bone affinity, etc. However, the comparatively low efficacy of these non-antibiotic properties along with adverse effects such as hyperpigmentation, phototoxicity, long-term skeletal retention, etc. have not helped their broad utilization similar to their use as an antibiotic. In a unique attempt to improve the non-antibiotic properties while reducing the adverse effects, we converted the TET to nano-carbons through partial carbonization. After sorting out two water-dispersible C-TETs (C-TET HT - hydrothermal and C-TET HP - hot plate) based on their improved antioxidant activity, they have been characterized through a host of analytical techniques that showed distinct differences in morphology, size, shape, and surface functionality. Excitingly, the C-TET HT and C-TET HP have shown differential biological activity in a dosage and time-dependent manner in terms of cytotoxicity, immunomodulation, and osteogenic activity that was found to be associated with their carbonized parameters. Overall, the carbonized nano-drugs, C-TET HT and C-TET HP have presented substantial early promises on their non-antibiotic properties that could be further explored to develop into some effective therapeutics.

Antibacterial functionalized carbon dots and their application in bacterial infections and inflammation

Bacterial infections and inflammation pose a severe threat to human health and the social economy. The existence of super-bacteria and the increasingly severe phenomenon of antibiotic resistance highlight the development of new antibacterial agents. Due to low cytotoxicity, high biocompatibility, and different antibacterial mechanisms from those for antibiotics, functionalized carbon dots (FCDs) promise a new platform for the treatment of bacterial infectious diseases. However, few articles have systematically sorted out the available antibacterial mechanisms for FCDs and their application in the treatment of bacterial inflammation. This review focuses on the available antibacterial mechanisms for FCDs, including covalent and non-covalent interactions, reactive oxygen species, photothermal therapy, and size effect. Meanwhile, the design of antibacterial FCDs is introduced, including surface modification, doping, and combination with other nanomaterials. Furthermore, this review specifically concentrates on the research advances of antibacterial FCDs in the treatment of bacterial inflammation. Finally, the advantages and challenges of applying FCDs in practical antimicrobial applications are discussed.

Machine Learning-Mediated Ultrasensitive Detection of Citrinin and Associated Mycotoxins in Real Food Samples Discerned from a Photoluminescent Carbon Dot Barcode Array

Economically viable remote sensing of foodborne contaminants using minimalistic chemical reagents and simultaneous automation calls for a concrete integration of a chemical detection strategy with artificial intelligence. In a first of its kind, we report the ultrasensitive detection of citrinin and associated mycotoxins like aflatoxin B1 and ochratoxin A using an Alizarin Red S (ARS) and cystamine-derived carbon dot (CD) that aptly amalgamate with machine learning algorithms for automation. The photoluminescence response of the CD as a function of various solvents and pH is used to generate array channels that are further modulated in the presence of the mycotoxins whose digital images were acquired to determine pixelation, essentially creating a barcode. The barcode was fed to machine learning algorithms that actualize and intertwine convoluted databases, demonstrating Extreme Gradient Boosting (XGBoost) as the optimized model out of eight algorithms tested. Spiked samples of wheat, rice, gram, maize, coffee, and milk were used to evaluate the testing model where an exemplary accuracy of 100% even at 10 pmol of mycotoxin concentration was achieved. Most importantly, the coexistence of mycotoxins could also be detected through the CD array and XGBoost synergy hinting toward a broader scope of the developed methodology for smart detection of foodborne contaminants.

Biocompatibility and Safety Assessment of Combined Topical Ozone and Antibiotics for Treatment of Infected Wounds

Wound infections with antibiotic-resistant bacteria, particularly the Gram-negative strains, pose a substantial health risk for patients with limited treatment options. Recently topical administration of gaseous ozone and its combination with antibiotics through portable systems has been demonstrated to be a promising approach to eradicate commonly found Gram-negative strains of bacteria in wound infections. However, despite the significant impact of ozone in treating the growing number of antibiotic-resistant infections, uncontrolled and high concentrations of ozone can cause damage to the surrounding tissue. Hence, before such treatments could advance into clinical usage, it is paramount to identify appropriate levels of topical ozone that are effective in treating bacterial infections and safe for use in topical administration. To address this concern, we have conducted a series of in vivo studies to evaluate the efficacy and safety of a portable and wearable adjunct ozone and antibiotic wound therapy system. The concurrent ozone and antibiotics are applied through a wound interfaced gas permeable dressing coated with water-soluble nanofibers containing vancomycin and linezolid (traditionally used to treat Gram-positive infections) and connected to a portable ozone delivery system. The bactericidal properties of the combination therapy were evaluated on an ex vivo wound model infected with Pseudomonas aeruginosa, a common Gram-negative strain of bacteria found in many skin infections with high resistance to a wide range of currently available antibiotics. The results indicated that the optimized combination delivery of ozone (4 mg h^-1) and topical antibiotic (200 μg cm^-2) provided complete bacteria eradication after 6 h of treatment while having minimum cytotoxicity to human fibroblast cells. Furthermore, in vivo local and systemic toxicity studies (e.g., skin monitoring, skin histopathology, and blood analysis) on pig models showed no signs of adverse effects of ozone and antibiotic combination therapy even after 5 days of continuous administration. The confirmed efficacy and biosafety profile of the adjunct ozone and antibiotic therapy places it as a strong candidate for treating wound infection with antimicrobial-resistant bacteria and further pursuing human clinical trials.

Chemiluminescent carbon nanodots for dynamic and guided antibacteria

Advanced antibacterial technologies are needed to counter the rapid emergence of drug-resistant bacteria. Image-guided therapy is one of the most promising strategies for efficiently and accurately curing bacterial infections. Herein, a chemiluminescence (CL)-dynamic/guided antibacteria (CDGA) with multiple reactive oxygen species (ROS) generation capacity and chemiexcited near-infrared emission has been designed for the precise theranostics of bacterial infection by employing near-infrared emissive carbon nanodots (CDs) and peroxalate as CL fuels. Mechanistically, hydrogen peroxide generated in the bacterial microenvironment can trigger the chemically initiated electron exchange between CDs and energy-riched intermediate originated from the oxidized peroxalate, enabling bacterial induced inflammation imaging. Meanwhile, type I/II photochemical ROS production and type III ultrafast charge transfer from CDs under the self-illumination can inhibit the bacteria proliferation efficiently. The potential clinical utility of CDGA is further demonstrated in bacteria infected mice trauma model. The self-illuminating CDGA exhibits an excellent in vivo imaging quality in early detecting wound infections and internal inflammation caused by bacteria, and further are proven as efficient broad-spectrum antibacterial nanomedicines without drug-resistance, whose sterilizing rate is up to 99.99%.

Preparations of antibacterial yellow-green-fluorescent carbon dots and carbon dots-lysozyme complex and their applications in bacterial imaging and bacteria/biofilm inhibition/clearance

The preparation of functional long-wavelength-emitting nanomaterials and the researches on their applications in antibacterial and antibiofilm fields have important significance. This paper reports the preparation of yellow-green-fluorescent and high- quantum yield carbon dots (4-ACDs) with 4-aminosalicylic acid and polyethylene imine as raw materials through one-step route, and the impacts of raw material structure and the reaction conditions upon the optical properties of the products have been investigated. 4-ACDs exhibit excellent broad-spectrum antibacterial activity, and their good biocompatibility ensures them as ideal fluorescent nano-probe for cell imaging. However, 4-ACDs could not effectively eliminate the biofilm of Staphylococcus aureus (S. aureus). CDs-LZM complex was prepared through the coupling between 4-ACDs and lysozyme (LZM) and the complex showed strong antibacterial activity against Gram-positive bacteria, particularly with MIC against S. aureus at 5 μg mL^-1. Besides, CDs-LZM showed excellent ability against the biofilm of S. aureus. At the concentration of 60 μg mL^-1, its inhibition rate against the growth of biofilm was 86 %, and elimination rate against biofilm reached 76 %. CDs-LZM exhibited obvious antibiofilm ability through removing extracellular matrix of biofilm, greatly reducing the thickness of biofilm under confocal microscopy. The application of novel long-wavelength-emitting nanomaterial in eliminating pathogenic bacteria is of great significance.

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.

Green Synthesis of Highly Fluorescent Carbon Dots from Bovine Serum Albumin for Linezolid Drug Delivery as Potential Wound Healing Biomaterial: Bio-Synergistic Approach, Antibacterial Activity, and In Vitro and Ex Vivo Evaluation

A simple and green approach was developed to produce novel highly fluorescent bovine serum albumin carbon dots (BCDs) via facile one-step hydrothermal treatment, using bovine serum albumin as a precursor carbon source. Inherent blue photoluminescence of the synthesized BCDs provided a maximum photostability of 90.5 ± 1.2% and was characterized via TEM, FT-IR, XPS, XRD, UV-visible, and zeta potential analyses. By virtue of their extremely small size, intrinsic optical and photoluminescence properties, superior photostability, and useful non-covalent interactions with the synthetic oxazolidinone antibiotic linezolid (LNZ), BCDs were investigated as fluorescent nano-biocarriers for LNZ drug delivery. The release profile of LNZ from the drug delivery system (LNZ-BCDs) revealed a distinct biphasic release, which is beneficial for mollifying the lethal incidents associated with wound infection. The effective wound healing performance of the developed LNZ-BCDs were evaluated through various in vitro and ex vivo assays such as MTT, ex vivo hemolysis, in vitro antibacterial activity, in vitro skin-related enzyme inhibition, and scratch wound healing assays. The examination of LNZ-BCDs as an efficient wound healing biomaterial illustrated excellent biocompatibility and low cytotoxicity against normal human skin fibroblast (HSF) cell line, indicating distinct antibacterial activity against the most common wound infectious pathogens including Staphylococcus aureus (ATCC^® 25922) and methicillin-resistant Staphylococcus aureus, robust anti-elastase, anti-collagenase, and anti-tyrosinase activities, and enhanced cell proliferation and migration effect. The obtained results confirmed the feasibility of using the newly designed fluorescent LNZ-BCDs nano-bioconjugate as a unique antibacterial biomaterial for effective wound healing and tissue regeneration. Besides, the greenly synthesized BCDs could be considered as a great potential substitute for toxic nanoparticles in biomedical applications due to their biocompatibility and intense fluorescence characteristics and in pharmaceutical industries as promising drug delivery nano-biocarriers for effective wound healing applications.

Neutrophil-mediated delivery of the combination of colistin and azithromycin for the treatment of bacterial infection

Novel treatment strategies are in urgent need to deal with the rapid development of antibiotic-resistant superbugs. Combination therapies and targeted drug delivery have been exploited to promote treatment efficacies. In this study, we loaded neutrophils with azithromycin and colistin to combine the advantages of antibiotic combinations, targeted delivery, and immunomodulatory effect of azithromycin to treat infections caused by Gram-negative pathogens. Delivery of colistin into neutrophils was mediated by fusogenic liposome, while azithromycin was directly taken up by neutrophils. Neutrophils loaded with the drugs maintained the abilitity to generate reactive oxygen species and migrate. In vitro assays demonstrated enhanced bactericidal activity against multidrug-resistant pathogens and reduced inflammatory cytokine production by the drug-loaded neutrophils. A single intravenous administration of the drug-loaded neutrophils effectively protected mice from Pseudomonas aeruginosa infection in an acute pneumonia model. This study provides a potential effective therapeutic approach for the treatment of bacterial infections.

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Neutrophils are loaded with colistin and azithromycin in vitro

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The loaded drugs enhance the bactericidal effect and reduce the inflammatory response

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Drug-loaded neutrophils conferred effective protection against bacterial infection

Wearable adjunct ozone and antibiotic therapy system for treatment of Gram-negative dermal bacterial infection

The problematic combination of a rising prevalence of skin and soft tissue infections and the growing rate of life-threatening antibiotic resistant infections presents an urgent, unmet need for the healthcare industry. These evolutionary resistances originate from mutations in the bacterial cell walls which prevent effective diffusion of antibiotics. Gram-negative bacteria are of special consideration due to the natural resistance to many common antibiotics due to the unique bilayer structure of the cell wall. The system developed here provides one solution to this problem through a wearable therapy that delivers and utilizes gaseous ozone as an adjunct therapy with topical antibiotics through a novel dressing with drug-eluting nanofibers (NFs). This technology drastically increases the sensitivity of Gram-negative bacteria to common antibiotics by using oxidative ozone to bypass resistances created by the bacterial cell wall. To enable simple and effective application of adjunct therapy, ozone delivery and topical antibiotics have been integrated into a single application patch. The drug delivery NFs are generated via electrospinning in a fast-dissolve PVA mat without inducing decreasing gas permeability of the dressing. A systematic study found ozone generation at 4 mg/h provided optimal ozone levels for high antimicrobial performance with minimal cytotoxicity. This ozone treatment was used with adjunct therapy delivered by the system in vitro. Results showed complete eradication of Gram-negative bacteria with ozone and antibiotics typically used only for Gram-positive bacteria, which showed the strength of ozone as an enabling adjunct treatment option to sensitize bacteria strains to otherwise ineffective antibiotics. Furthermore, the treatment is shown through biocompatibility testing to exhibit no cytotoxic effect on human fibroblast cells.

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.

Progress Report: Antimicrobial Drug Discovery in the Resistance Era

Antibiotic resistance continues to be a most serious threat to public health. This situation demands that the scientific community increase their efforts for the discovery of alternative strategies to circumvent the problems associated with conventional small molecule therapeutics. The Global Antimicrobial Resistance and Use Surveillance System (GLASS) Report (published in June 2021) discloses the rapidly increasing number of bacterial infections that are mainly caused by antimicrobial-resistant bacteria. These concerns have initiated various government agencies and other organizations to educate the public regarding the appropriate use of antibiotics. This review discusses a brief highlight on the timeline of antimicrobial drug discovery with a special emphasis on the historical development of antimicrobial resistance. In addition, new antimicrobial targets and approaches, recent developments in drug screening, design, and delivery were covered. This review also discusses the emergence and roles of various antibiotic adjuvants and combination therapies while shedding light on current challenges and future perspectives. Overall, the emergence of resistant microbial strains has challenged drug discovery but their efforts to develop alternative technologies such as nanomaterials seem to be promising for the future.

A simple fluorescent strategy for liver capillary labeling with carbon quantum dot-lectin nanoprobe

Based on lycopersicon esculentum lectin that can target vascular endothelial cells and carbon quantum dots, we designed a carbon-based probe for the fluorescence labeling and imaging of hepatic blood vessels of liver tissue sections.

Photocatalytic nanoparticles - From membrane interactions to antimicrobial and antiviral effects

As a result of increasing resistance among pathogens against antibiotics and anti-viral therapeutics, nanomaterials are attracting current interest as antimicrobial agents. Such materials offer triggered functionalities to combat challenging infections, based on either direct membrane action, effects of released ions, thermal shock induced by either light or magnetic fields, or oxidative photocatalysis. In the present overview, we focus on photocatalytic antimicrobial effects, in which light exposure triggers generation of reactive oxygen species. These, in turn, cause oxidative damage to key components in bacteria and viruses, including lipid membranes, lipopolysaccharides, proteins, and DNA/RNA. While an increasing body of studies demonstrate that potent antimicrobial effects can be achieved by photocatalytic nanomaterials, understanding of the mechanistic foundation underlying such effects is still in its infancy. Addressing this, we here provide an overview of the current understanding of the interaction of photocatalytic nanomaterials with pathogen membranes and membrane components, and how this translates into antibacterial and antiviral effects.

Fluorescent Carbon Dot-Curcumin Nanocomposites for Remarkable Antibacterial Activity with Synergistic Photodynamic and Photothermal Abilities

Photosensitizer (PS)-mediated photodynamic therapy (PDT) has attracted more and more attention as an alternative to traditional antibiotic therapy. Nevertheless, the limitations of traditional photosensitizers seriously hinder their practical application, as a result, the methods to improve the antibacterial properties of traditional photosensitizers have become a hot topic in the field of photomedicine. Herein, a compound nano-PS system has been constructed with synergistic photodynamic and photothermal (PTT) antibacterial effects, triggered by a dual-wavelength illumination. Fluorescent carbon dots (CDs) were synthesized and employed as carriers for the delivery of curcumin (Cur) to obtain CDs/Cur. Upon combined near-infrared and 405 nm visible dual-wavelength irradiation, CDs/Cur could simultaneously generate ROS and a moderate temperature increase, triggering synergistic antibacterial effects against both Gram-positive and Gram-negative bacteria. The results of scanning electron microscopy and fluorescence confocal imaging showed that the combined effect of CDs/Cur with PDT and PTT caused more serious damage to the cell membrane. In addition, CDs/Cur exhibited low cytotoxicity and negligible hemolytic activity, showing great biocompatibility. Therefore, the construction of CDs/Cur by employing CDs as photosensitizer delivery carriers provides a strategy for the improvement of the antibacterial effect of the photosensitizer and the design of next-generation antibacterial agents in photomedicine.

Visible light-induced charge injection and migration in self-assembled carbon dot-DNA-carbon dot nano-dumbbell obtained through controlled stoichiometric conjugation

The potential of carbon dots (CDs) for photonic conversion to charged states, together with the ability of DNA to transport such charge for extensive charge separation, offers an opportunity to control directionality of migration for photo-induced radical cations in CD-DNA based nano-assemblies. This is achieved through engineering the reaction valency of CDs whereby one CD is covalently conjugated with one ssDNA strand. Subsequently, a CD-DNA-CD nano-dumbbell architecture was created through hybridization mediated self-assembly. The time and intensity-dependent transduction of visible light photonic energy to chemical potential in DNA was achieved through irradiation of 1,4-diaminoathraquinone and glyoxal derived CD with 100 W tungsten source and natural sunlight. Following charge injection by CD, the radical cation migration in DNA was perceived through trapping of the hole in repeated GG steps in the DNA. Overall, a breakthrough in visible-light-induced charge transfer by CD into DNA was achieved, potentially applicable to optobioelectronics.

Injectable niclosamide nanohybrid as an anti-SARS-CoV-2 strategy

COVID-19 is a rapidly evolving emergency, which necessitates scientific community to come up with novel formulations that could find quick relief to the millions affected around the globe. Remdesivir being the only injectable drug by FDA for COVID-19, it initially showed promising results, however, later on failed to retain its claims, hence rejected by the WHO. Therefore, it is important to develop injectable formulation that are effective and affordable. Here in this work, we formulated poly ethylene glycol (PEG) coated bovine serum albumin (BSA) stabilized Niclosamide (NIC) nanoparticles (NPs) (∼BSA-NIC-PEG NPs) as an effective injectable formulation. Here, serum albumin mediated strategy was proposed as an effective strategy to specifically target SARS-CoV-2, the virus that causes COVID-19. The in-vitro results showed that the developed readily water dispersible formulation with a particle size <120 nm size were well stable even after 3 weeks. Even though the in-vitro studies showed promising results, the in-vivo pharmaco-kinetic (PK) study in rats demands the need of conducting further experiments to specifically target the SARS-CoV-2 in the virus infected model. We expect that this present formulation would be highly preferred for targeting hypoalbuminemia conditions, which was often reported in elderly COVID-19 patients. Such studies are on the way to summarize its potential applications in the near future.

Covalent Conjugation of Carbon Dots with Plasmid and DNA Condensation Thereafter: Realistic Insights into the Condensate Morphology, Energetics, and Photophysics

The use of carbon quantum dots (CDs) as trackable nanocarriers for plasmid and gene as hybrid DNA condensates has gained momentum, as evident from the significant recent research efforts. However, the in-depth morphology of the condensates, the energetics of the condensation process, and the photophysical aspects of the CD are not well understood and often disregarded. Herein, for the first time, we covalently attached linearized pUC19 with citric acid and cysteamine-derived CD through the reaction of the surface amine groups of CDs with the 5'-phospho-methyl imidazolide derivative of the plasmid to obtain a 1:1 CD-pUC19 covalent conjugate. The CD-pUC19 conjugates were further transformed into DNA condensates with spermine that displayed a toroidal morphology with a diameter of ∼200 nm involving ∼2-5 CD-pUC19 conjugates in a single condensate. While the interaction of pristine CD to spermine was exothermic, the binding of the CD-pUC19 conjugate with spermine was endothermic and primarily entropy-driven. The condensed plasmid displayed severe conformational stress and deviation from the B-form due to the compact packing of the DNA but better transfection ability than the pristine CD. The CDs in the condensates tend to come close to each other at the core that results in their shielding from excitation. However, this does not prevent them from emanating reactive oxygen species on visible light exposure that compromises the decondensation process and cell viability at higher exposure times, calling for utmost caution in establishing them as nonviral transfecting agents universally.

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.

Homology and Immune Checkpoint Dual-Targeted Sonocatalytic Nanoagents for Enhancing Sonodynamic Tumor Therapy

Sonocatalytic nanoagents (SCNs), a kind of sonosensitizers, could catalyze oxygen to generate abundant reactive oxygen species (ROS) under stimulations of noninvasive and deep-penetrating ultrasound (US), which is commonly used for sonodynamic therapy (SDT) of tumors such as malignant melanoma. However, poor bioavailability of most SCNs and fast quenching of extracellular-generating ROS from SDT limit further applications of SCNs in the SDT of tumors. Herein, we synthesized a new kind of TiO2-based SCN functionalized with the malignant melanoma cell membrane (B16F10M) and programmed cell death-ligand 1 antibody (aPD-L1) for homology and immune checkpoint dual-targeted and enhanced sonodynamic tumor therapy. Under US irradiation, the synthesized SCN can catalytically generate a large amount of 1O2. In vitro experiments validate that functionalized SCNs exhibit precise targeting effects, high tumor cell uptake, and intracellular sonocatalytic killing of the B16F10 cells by a large amount of localized ROS. Utilizing the melanoma animal model, the functionalized SCN displays visible long-term retention in the tumor area, which assists the homology and immune checkpoint synergistically dual-targeted and enhanced in vivo SDT of the tumor. We suggest that this highly bioavailable and dual-functionalized SCN may provide a promising strategy and nanoplatform for enhancing sonodynamic tumor therapies.

Multifunctional N-Doped Carbon Dots for Bimodal Detection of Bilirubin and Vitamin B12, Living Cell Imaging, and Fluorescent Ink

A N-doped carbon dot (NCD) has been synthesized via a simplistic one-step hydrothermal technique using l-aspartic acid and 3,6-diaminoacridine hydrochloride. The NCDs exhibit a high quantum yield (22.7%) and excellent optical stability in aqueous media. Additionally, NCDs display good solid-state yellowish-green emission and are suitable for security ink applications. The remarkable fluorescence (FL) properties of NCDs are further applied to develop a multifunctional sensor for bilirubin (BR) and vitamin B₁₂ (VB12) via fluorescence quenching. We have systematically studied the FL quenching mechanisms of the two analytes. The primary quenching mechanism of BR is via the Förster resonant energy transfer (FRET) pathway facilitated by the H-bonding network between the hydrophilic moieties existing at the surface of BR and NCDs. In contrast, the inner filter effect (IFE) is mainly responsible for the recognition of VB12. The practicability of the nanoprobe NCDs is further tested in real-sample analysis for BR (human serum and urine samples) and VB12 (VB12 tablets, human serum, and energy drink) with a satisfactory outcome. The in vitro competency is also verified in the human cervical cancer cell line (HeLa cell) with negligible cytotoxicity and significant biocompatibility. This result facilitates the application of NCDs for bioimaging and recognition of VB12 in a living organism.

Expanding the Limits of Photodynamic Therapy: The Design of Organelles and Hypoxia-Targeting Nanomaterials for Enhanced Photokilling of Cancer

Photodynamic therapy (PDT) is a minimally invasive clinical protocol that combines a nontoxic photosensitizer (PS), appropriate visible light, and molecular oxygen for cancer treatment. This triad generates reactive oxygen species (ROS) in situ, leading to different cell death pathways and limiting the arrival of nutrients by irreversible destruction of the tumor vascular system. Despite the number of formulations and applications available, the advancement of therapy is hindered by some characteristics such as the hypoxic condition of solid tumors and the limited energy density (light fluence) that reaches the target. As a result, the use of PDT as a definitive monotherapy for cancer is generally restricted to pretumor lesions or neoplastic tissue of approximately 1 cm in size. To expand this limitation, researchers have synthesized functional nanoparticles (NPs) capable of carrying classical photosensitizers with self-supplying oxygen as well as targeting specific organelles such as mitochondria and lysosomes. This has improved outcomes in vitro and in vivo. This review highlights the basis of PDT, many of the most commonly used strategies of functionalization of smart NPs, and their potential to break the current limits of the classical protocol of PDT against cancer. The application and future perspectives of the multifunctional nanoparticles in PDT are also discussed in some detail.

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.

Synthesis of carbon dot-ZnO-based nanomaterials for antibacterial application

ZnO-based antibacterial materials have attracted significant attention in academia and industry.

Hybrid DNA-Carbon Dot-Poly(vinylpyrrolidone) Hydrogel with Self-Healing and Shape Memory Properties for Simultaneous Trackable Drug Delivery and Visible-Light-Induced Antimicrobial Photodynamic Inactivation

A two-step methodology for simultaneous conjugation of DNA and poly(vinylpyrrolidone) (PVP) polymer to a single carbon quantum dot (CD) is demonstrated for the first time to fabricate a pH-responsive DNA-CD-PVP hybrid hydrogel. Cross-linking in the hydrogel was achieved using CD as the common nucleus through the formation of DNA I-motif conformation at neutral to acidic pH and noncovalent interaction of PVP that infuse self-healing and shape memory properties in the hydrogel. The hydrogel is capable of loading and sustained delivery of drugs for more than 2 weeks as demonstrated using a model drug, Hemin. The quenching of fluorescence of CD by Hemin was trackable even through simple visual monitoring, which showed that Hemin can diffuse from the loaded part to the unloaded part of the hydrogel during the self-healing process. Most significantly, the chosen CD generates reactive oxygen species (ROS) upon visible light irradiation, armoring the hydrogel with worthy antimicrobial activity. Biocompatibility of the DNA-CD-PVP hydrogel was established on human fibroblast cells, indicating their potential use in biomedical area pertaining to wound healing.

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.

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.

Ultrasmall Ag2Te Quantum Dots with Rapid Clearance for Amplified Computed Tomography Imaging and Augmented Photonic Tumor Hyperthermia

With the fast development of nanomedicine, the imaging-guided and photo-induced cancer monotherapies can efficiently eliminate tumor lesions, which are strongly dependent on the construction of versatile theranostic nanoplatforms. Among diverse photo-converting nanoplatforms, silver chalcogenide nanoparticles feature high biocompatibility, narrow band gaps, and tunable optical properties, yet Ag₂Te-based nanosystems are still at a proof-of-concept stage, and the exploration of Ag₂Te-based nanosystems suitable for photonic tumor hyperthermia is challenging. Herein, we report on the construction of versatile ultrasmall Ag₂Te quantum dots (QDs) via a facile biomineralization strategy. Especially, these Ag₂Te QDs with negligible toxicity and excellent biocompatibility were developed for X-ray computed tomography (CT) imaging-guided photonic tumor hyperthermia by near-infrared (NIR) activation. The fabricated Ag₂Te QDs exhibited a high tumor suppression rate (94.3%) on 4T1 breast tumor animal models due to the high photothermal-conversion efficiency (50.5%). Mechanistically, Ag₂Te QDs were promising potential CT imaging agents for imaging guidance and monitoring during photonic hyperthermia. Importantly, Ag₂Te QDs were rapidly eliminated from the body via feces and urine because of their ultrasmall sizes. This work not only broadens the biomedical applications of silver chalcogenide-based theranostic nanosystems but also provides the paradigm of theranostic nanosystems with a photonic tumor hyperthermia effect and outstanding contrast enhancement of high-performance CT imaging.

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.

Photonic Carbon Dots as an Emerging Nanoagent for Biomedical and Healthcare Applications

As a class of carbon-based nanomaterials, carbon dots (CDs) have attracted enormous attention because of their tunable optical and physicochemical properties, such as absorptivity and photoluminescence from ultraviolet to near-infrared, high photostability, biocompatibility, and aqueous dispersity. These characteristics make CDs a promising alternative photonic nanoagent to conventional fluorophores in disease diagnosis, treatment, and healthcare managements. This review describes the fundamental photophysical properties of CDs and highlights their recent applications to bioimaging, photomedicine (e.g., photodynamic/photothermal therapies), biosensors, and healthcare devices. We discuss current challenges and future prospects of photonic CDs to give an insight into developing vibrant fields of CD-based biomedicine and healthcare.

Cascade of reactive oxygen species generation by polyprodrug for combinational photodynamic therapy

The redox status of cancer cells is well regulated by the balance between the reactive oxygen species (ROS) generation and elimination. Thus, the overall elevation of ROS level above the cellular tolerability threshold would lead to apoptotic or necrotic cell death. Herein, cinnamaldehyde (CA), a kind of oxidative stress amplified agent, was combined with photosensitizer pheophorbide A (PA) to promote the generation of ROS though synergistically endogenous and exogenous pathways. Firstly, acid-responsive polygalactose-co-polycinnamaldehyde polyprodrug (termed as PGCA) was synthesized, which could self-assemble into stable nanoparticles for the delivery of PA (termed as PGCA@PA NPs). The abundant expression of galactose receptor on tumor cells facilitated the positive targeting and cellular uptake efficiency of PGCA@PA NPs, after which PA could be synchronously released in company with the intracellular disassembly of PGCA NPs, due to the detaching of CA moieties under acidic microenvironment in endo/lysosomal compartment. Significantly increased ROS level was induced by the combined action of CA and PA with light irradiation, resulting in dramatically enhanced apoptosis of cancer cells. Importantly, intravenous injection of PGCA@PA NPs potently inhibited the tumor growth in hepatocellular carcinoma with negligible adverse effects. Moreover, combined with anti-programmed cell death protein 1 (anti-PD-1) therapy, PGCA@PA NPs treatment elicited anti-melanoma T-cell immune response and significantly promoted T cells infiltration in tumors. Hence, this novel polyprodrug nano delivery system was able to target and modulate the unique redox regulatory mechanisms of cancer cells through endogenous and exogenous pathways, providing a feasible approach to achieve synergetic therapeutic activity and selectivity.

Carbon dot cross-linked polyvinylpyrrolidone hybrid hydrogel for simultaneous dye adsorption, photodegradation and bacterial elimination from waste water

The creation of a polymeric hydrogel from polyvinylpyrrolidone (PVP) cross-linked by Carbon Quantum Dots (CD) for the adsorption and photocatalytic degradation of both cationic and anionic dyes. PVP, an important biocompatible constituent and often surplus in cosmetic industry, was carboxylated through NaOH refluxing and covalently conjugated to surface amine functionality of CD derived from lemon juice and Cysteamine. The hybrid hydrogel was obtained from PVP-CD covalent conjugate by careful manipulation of pH and found to possess better rheological properties than only carboxylate-PVP. The monolayer physisorption of the dyes on the hydrogel was affected by hydrogen bonding, dispersion or inductive effect, and π-π interaction with the polymer backbone as well as the CD that followed pseudo-second-order kinetics. Degradation of the adsorbed dyes was instated by the unique Reactive Oxygen Species (ROS) generating ability of the CD embedded in the hydrogel matrix upon exposure to sunlight, the mechanism of which is also unveiled. The same CD-induced ROS was found to effectively annihilate both gram-positive and gram-negative bacteria in real polluted water in less than 10 min of photoexcitation of the hydrogel. The hydrogel was restored by mild acid wash that is able to perform dye adsorption and photo-degradation upto four cycles.