Recent Developments in Synthesis and Photocatalytic Applications of Carbon Dots

Nitrogen doped carbon dots for in vitro intracellular redox modulation via optical stimulation

Carbon dots (CDs) are promising candidates as oxygen photosensitizers, in cancer therapeutic applications due to their high quantum yield, superior chemical and photostability, low cytotoxicity and ease of chemical functionalization/tuning. Nitrogen doping can further improve oxygen photosensitization performance. Besides photodynamic therapy, however, the possibility to finely and remotely regulate the intracellular redox balance by using physical stimuli has been attracting more and more interest not only for nanotheranostic application, but also as a novel, fully biocompatible therapeutic tool. Here, we report on the synthesis of nitrogen-doped CDs by solvothermal methods starting from abundant, bioderived, low-cost precursors, and we characterize their interface with in vitro cultures of human embryonic kidney (HEK-293) cells, a widely accepted model of non-tumoral cells. While not affecting cell proliferation, synthesized CDs efficiently modulate, under visible light and physiological eustress conditions, intracellular calcium ion dynamics and reactive oxygen species concentration, resulting in a 4-fold increase. The reported results may broaden the application of CDs beyond photodynamic therapy, unveiling new opportunities in the field of redox medicine assisted by carbon-based nanomaterials and optical stimulation.

Efficient tetracycline degradation using carbon quantum dot modified TiO2@LaFeO3 hollow core shell photocatalysts

Efficient harnessing of solar energy presents a significant challenge in environmental cleanup efforts. This study develops a highly effective carbon quantum dots-modified hollow core-shell TiO2-LaFeO3 heterojunction photocatalyst (CDs-TLFO). Structural analysis confirmed that nanosheets are loaded with CQDs, forming a hollow core-shell structure with intimate interconnection. Photocatalytic experiments reveal that CDs-TLFO degrads tetracycline hydrochloride (TC) 2.02 times faster than TLFO alone, and significantly outperformes h-TiO2 and LaFeO3 (11.28 and 2.78 times, respectively). This enhancement is attributed to CQDs acting as electron acceptors with upconversion properties, enhancing the separation of e--h+ pairs and boosting visible light absorption. Integration of CQDs onto the TLFO surface creates numerous active sites and enhances visible light absorption. SEM and TEM tests confirm that the catalyst has a hollow core-shell structure. ESR tests and radical trapping experiments indicate that the high degradation efficiency of the catalyst mainly owns to the synergistic effect of hydroxyl radicals (·OH) and superoxide radicals (·O2-). The reusability and stability of the catalysts are investigated, potential TC degradation pathways are proposed as well as the photocatalytic reaction mechanism is revealed. This research introduces promising avenues for environmental cleanup and offers a straightforward, energy-efficient, and environmentally friendly method for producing CDs-TLFO heterojunction materials with superior photocatalytic capabilities.

Functional Bio-Based Polymeric Hydrogels for Wastewater Treatment: From Remediation to Sensing Applications

In recent years, many researchers have focused on designing hydrogels with specific functional groups that exhibit high affinity for various contaminants, such as heavy metals, organic pollutants, pathogens, or nutrients, or environmental parameters. Novel approaches, including cross-linking strategies and the use of nanomaterials, have been employed to enhance the structural integrity and performance of the desired hydrogels. The evolution of these hydrogels is further highlighted, with an emphasis on fine-tuning features, including water absorption capacity, environmental pollutant/factor sensing and selectivity, and recyclability. Furthermore, this review investigates the emerging topic of stimuli-responsive smart hydrogels, underscoring their potential in both sorption and detection of water pollutants. By critically assessing a wide range of studies, this review not only synthesizes existing knowledge, but also identifies advantages and limitations, and describes future research directions in the field of chemically engineered hydrogels for water purification and monitoring with a low environmental impact as an important resource for chemists and multidisciplinary researchers, leading to improvements in sustainable water management technology.

Graphene-Based Photodynamic Therapy and Overcoming Cancer Resistance Mechanisms: A Comprehensive Review

Photodynamic therapy (PDT) is a non-invasive therapy that has made significant progress in treating different diseases, including cancer, by utilizing new nanotechnology products such as graphene and its derivatives. Graphene-based materials have large surface area and photothermal effects thereby making them suitable candidates for PDT or photo-active drug carriers. The remarkable photophysical properties of graphene derivates facilitate the efficient generation of reactive oxygen species (ROS) upon light irradiation, which destroys cancer cells. Surface functionalization of graphene and its materials can also enhance their biocompatibility and anticancer activity. The paper delves into the distinct roles played by graphene-based materials in PDT such as photosensitizers (PS) and drug carriers while at the same time considers how these materials could be used to circumvent cancer resistance. This will provide readers with an extensive discussion of various pathways contributing to PDT inefficiency. Consequently, this comprehensive review underscores the vital roles that graphene and its derivatives may play in emerging PDT strategies for cancer treatment and other medical purposes. With a better comprehension of the current state of research and the existing challenges, the integration of graphene-based materials in PDT holds great promise for developing targeted, effective, and personalized cancer treatments.

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

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

Chemical- and green-precursor-derived carbon dots for photocatalytic degradation of dyes

Rapid industrialization and untreated industrial effluents loaded with toxic and carcinogenic contaminants, especially dyes that discharge into environmental waters, have led to a rise in water pollution, with a substantial adverse impact on marine life and humankind. Photocatalytic techniques are one of the most successful methods that help in degradation and/or removal of such contaminants. In recent years, semiconductor quantum dots are being substituted by carbon dots (CDs) as photocatalysts, due to the ease of formation, cost-effectiveness, possible sustainability and scalability, much lower toxicity, and above all its high capacity to harvest sunlight (UV, visible, and near infrared) through electron transfer that enhances the lifetime of the photogenerated charge carriers. A better understanding between the properties of the CDs and their role in photocatalytic degradation of dyes and contaminants is required for the formation of controllable structures and adjustable outcomes. The focus of this review is on CDs and its composites as photocatalysts obtained from different sustainable green as well as chemical precursors. Apart from the synthesis, characterization, and properties of the CDs, the study also highlights the effect of different parameters on the photocatalytic properties of CDs and their composites for catalytic dye degradation mechanisms in detail. Besides the present research development in the field, potential challenges and future perspectives are also presented.

Fluorescent carbon dots synthesized by waste wind turbine blade for photocatalytic degradation

Developing novel waste recycling strategies has become a feasible solution to overcome environmental pollution. In this work, a method of using waste wind turbine blade (WTB) as a carbon source to synthesize blue fluorescent carbon dots (B-CDs) by hydrothermal treatment is proposed. B-CDs are spherical and have an average particle size of 5.2 nm. The surface is rich in C-O, C=O, -CH3 , and N-H bond functional groups, containing five elements: C, O, N, Si, and Ca. The optimal emission wavelength of B-CDs is 463 nm, corresponding to an excitation wavelength of 380 nm. Notably, a relatively high quantum yield of 29.9% and a utilization rate of 40% were obtained. In addition, B-CDs can serve as a photocatalyst to degrade methylene blue dye, with a degradation efficiency of 64% under 40-min irradiation conditions. The presence of holes has a significant influence on the degradation process.

Nanostructured N/S doped carbon dots/mesoporous silica nanoparticles and PVA composite hydrogel fabrication for anti-microbial and anti-biofilm application

Regarding the convergence of the worldwide epidemic, the appearance of bacterial infection has occasioned in a melodramatic upsurge in bacterial pathogens with confrontation against one or numerous antibiotics. The implementation of engineered nanostructured particles as a delivery vehicle for antimicrobial agent is one promising approach that could theoretically battle the setbacks mentioned. Among all nanoparticles, silica nanoparticles have been found to provide functional features that are advantageous for combatting bacterial contagion. Apart from that, carbon dots, a zero-dimension nanomaterial, have recently exhibited their photo-responsive property to generate reactive oxygen species facilitating to enhance microorganism suppression and inactivation ability. In this study, potentials of core/shell mesoporous silica nanostructures (MSN) in conjugation with carbon dots (CDs) toward antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli have been investigated. Nitrogen and sulfur doped CDs (NS/CDs) conjugated with MSN which were cost effective nanoparticles exhibited much superior antimicrobial activity for 4 times as much as silver nanoparticles against all bacteria tested. Among all nanoparticles tested, 0.40 M NS/CDs@MSN showed the greatest minimal biofilm inhibitory at very low concentration (< 0.125 mg mL-1), followed by 0.20 M NS/CDs@MSN (0.5 mg mL-1), CD@MSN (25 mg mL-1), and MSN (50 mg mL-1), respectively. Immobilization of NS/CDs@MSN in polyvinyl alcohol (PVA) hydrogel was performed and its effect on antimicrobial activity, biofilm controlling efficiency, and cytotoxicity toward fibroblast (NIH/3 T3 and L-929) cells was additionally studied for further biomedical applications. The results demonstrated that 0.40 M NS/CDs-MSN@PVA hydrogel exhibited the highest inhibitory effect on S. aureus > P. aeruginosa > E. coli. In addition, MTT assay revealed some degree of toxicity of 0.40 M NS/CDs-MSN@PVA hydrogel against L-929 cells by a slight reduction of cell viability from 100% to 81.6% when incubated in the extract from 0.40 M NS/CDs-MSN@PVA hydrogel, while no toxicity of the same hydrogel extract was detected toward NIH/3 T3 cells.

Boron-doped graphene quantum dot/bismuth molybdate composite photocatalysts for efficient photocatalytic nitrogen fixation reactions

Bismuth molybdate (BMO) is a promising visible-driven photocatalyst and constructing heterojunctions in BMO-based materials is an effective way to enhance photocatalytic performance. In this study, boron-doped graphene quantum dots (BGQDs) were synthesized by one-step pyrolysis and carbonization, followed by the preparation of bismuth molybdate/boron-doped graphene quantum dots (BGQDs/BMO) heterojunction photocatalysts using in-situ growth method. The introduction of BGQDs significantly improved the photocatalytic nitrogen fixation activity under the irradiation of visible light and without scavengers. The highest NH3 yield was achieved with BGQDs/BMO-10, which was 3.48 times higher than pure phase BMO. This improvement was due to the formation of Z-scheme heterojunctions between BGQDs and BMO with the synergistic mechanism of interfacial charge transport and the generation of more protons. This study provides useful guidance for enhancing the visible-light nitrogen fixation performance of BMO materials.

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as in vitro antimicrobial drug nanocarrier

Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min-1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min-1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL-1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications.

Visible-Light-Activated Carbon Dot Photocatalyst for ROS-Mediated Inhibition of Algae Growth

The growing occurrence of detrimental algal blooms resulting from industrial and agricultural activities emphasizes the urgency of implementing efficient removal strategies. In this study, we have successfully synthesized stable and biocompatible carbon dots (R-CDs) capable of generating reactive oxygen species (ROS) upon exposure to natural light irradiation. Phaeocystis globosa Scherffel (PGS) was selected as a representative model for conducting anti-algal experiments. Remarkably, in the presence of R-CDs, the complete eradication of harmful algae within a simulated light exposure period of 27 h was achieved. Furthermore, fluorescence lifetime imaging microscopy (FLIM) was first employed to study the physiological processes involved in the oxidative stress induced by PGS when subjected to ROS attack. The findings of this study demonstrate the potential of R-CDs as a highly promising anti-algal agent. This elucidation of the mechanism contributes to a comprehensive understanding of the efficacy and effectiveness of such agents in combating algal growth, further inspiring the development of other anti-algal agents.

The Effect of Electro-Induced Multi-Gas Modification on Polymer Substrates’ Surface Structure for Additive Manufacturing

We investigated the effect of electro-induced multi-gas modification (EIMGM) duration on the adhesion and wear resistance of PET and LDPE polymer substrates used in the printing industry. It was found that EIMGM increases the polar component and the complete free surface energy from 26 to 57 mJ/m2 for LDPE and from 37 to 67 mJ/m2 for PET (due to the formation of oxygen-containing groups on the surface of the materials). Although the degree of textural and morphological heterogeneity of the modified LDPE increased more than twice compared to the initial state, it is not still suitable for application as a substrate in extrusion 3D printing. However, for PET, the plasma-chemical modification contributed to a significant increase (~5 times) in filament adhesion to its surface (due to chemical and morphological transformations of the surface layers) which allows for using the FFF technology for additive prototyping on the modified PET-substrates.

Carbon nanodots with a controlled N structure by a solvothermal method for generation of reactive oxygen species under visible light

Carbon nanodots can function as photosensitizers that have the ability to generate reactive oxygen species such as singlet oxygen, hydroxy (OH) radicals, and superoxide ions. However, most of these can only be generated upon ultraviolet light excitation. Additionally, the mechanism of reactive oxygen species generation by carbon nanodots remains unclear. The development of carbon nanodots that can photosensitize under visible light irradiation is desirable for applications such as photodynamic therapy and pollutant decomposition under visible light. Here, we report novel carbon nanodot-based photosensitizers that generate reactive oxygen species under visible light; they were synthesized using a solvothermal method with two solvents (formamide and water) and amidol as the carbon source. Carbon nanodots from the solvothermal synthesis in formamide showed blue fluorescence, while those obtained in water showed green fluorescence. The photo-excited blue-fluorescent carbon nanodots produced OH radicals, superoxide ions, and singlet oxygen, and therefore could function as both type I and type II photosensitizers. In addition, photo-excited green-fluorescent carbon nanodots generated only singlet oxygen, therefore functioning as type II photosensitizers. It is proposed that the two photosensitizers have different origins of reactive oxygen species generation: the enrichment of graphitic N for blue-fluorescent carbon nanodots and molecular fluorophores for green-fluorescent carbon nanodots.

A critical review on the environmental applications of carbon dots

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

From Rice Husk Ash to Silica-Supported Carbon Nanomaterials: Characterization and Analytical Application for Pre-Concentration of Steroid Hormones from Environmental Waters

Rice husk (RH) in the rice industry is often air-burnt to obtain energy in the form of heat and RH ash (RHA) residue. In this work, RHA was applied as a starting material to obtain silica-supported carbon nanomaterials, resulting in a new reuse of a globally produced industrial waste product, in a circular economy approach. The preparation involves ultrasound-assisted one-pot oxidation with a sulfonitric mixture followed by wet oven treatment in a closed vessel. A study of oxidation times and RHA amount/acid volume ratio led to a solid material (nC-RHA@SiO2) and a solution containing silica-supported carbon quantum dots (CQD-RHA@SiO2). TEM analyses evidenced that nC-RHA@SiO2 consists of nanoparticle aggregates, while CQD-RHA@SiO2 are carbon-coated spherical silica nanoparticles. The presence of oxygenated carbon functional groups, highlighted by XPS analyses, makes these materials suitable for a wide range of analytical applications. As the main product, nC-RHA@SiO2 was tested for its affinity towards steroid hormones. Solid-phase extractions were carried out on environmental waters for the determination of target analytes at different concentrations (10, 50, and 200 ng L−1), achieving quantitative adsorption and recoveries (RSD < 20%, n = 3). The method was successfully employed for monitoring lake, river, and wastewater treatment plant water samples collected in Northern Italy.

Potential Development of N-Doped Carbon Dots and Metal-Oxide Carbon Dot Composites for Chemical and Biosensing

Among carbon-based nanomaterials, carbon dots (CDs) have received a surge of interest in recent years due to their attractive features such as tunable photoluminescence, cost effectiveness, nontoxic renewable resources, quick and direct reactions, chemical and superior water solubility, good cell-membrane permeability, and simple operation. CDs and their composites have a large potential for sensing contaminants present in physical systems such as water resources as well as biological systems. Tuning the properties of CDs is a very important subject. This review discusses in detail heteroatom doping (N-doped CDs, N-CDs) and the formation of metal-based CD nanocomposites using a combination of matrices, such as metals and metal oxides. The properties of N-CDs and metal-based CDs nanocomposites, their syntheses, and applications in both chemical sensing and biosensing are reviewed.

Carbon dots-based nanomaterials for fluorescent sensing of toxic elements in environmental samples: Strategies for enhanced performance

Rapid industrialization and manufacturing expansion have caused heavy metal pollution, which is a critical environmental issue faced by global population. In addition, the disadvantages presented by conventional detection methods such as the requirement of sophisticated instruments and qualified personnel have led to the development of novel nanosensors. Recently, carbon dots (CDs) have been presented as a multifunctional nanomaterial alternative for the accurate detection of heavy metal ions in water systems. The capacity of CDs to detect contaminants in wastewater -including heavy metals- can be found in the literature; however, to the best of our knowledge, none of them discusses the most recent strategies to enhance their performance. Therefore, in this review, beyond presenting successful examples of the use of CDs for the detection of metal ions, we further discuss the strategies to enhance their photoluminescence properties and their performance for environmental monitoring. In this manner, strategies such as heteroatom-doping and surface passivation are reviewed in detail, as well as describing the mechanisms and the effect of precursors and synthesis methods. Finally, the current challenges are described in detail to propose some recommendations for further research.

Facile preparation of aqueous-soluble fluorescent polyethylene glycol functionalized carbon dots from palm waste by one-pot hydrothermal carbonization for colon cancer nanotheranostics

Carbon dots (CDs) are categorized as an emerging class of zero-dimension nanomaterials having high biocompatibility, photoluminescence, tunable surface, and hydrophilic property. CDs, therefore, are currently of interest for bio-imaging and nano-medicine applications. In this work, polyethylene glycol functionalized CDs (CD-PEG) were prepared from oil palm empty fruit bunch by a one-pot hydrothermal technique. PEG was chosen as a passivating agent for the enhancement of functionality and photoluminescence properties of CDs. To prepare the CDs-PEG, the effects of temperature, time, and concentration of PEG were investigated on the properties of CDs. The as-prepared CDs-PEG were characterized by several techniques including dynamic light scattering, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, fluorescence spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy and Thermogravimetric analysis. The as-prepared CDs under hydrothermal condition at 220 °C for 6 h had spherical morphology with an average diameter of 4.47 nm. Upon modification, CDs-PEG were photo-responsive with excellent photoluminescence property. The CDs-PEG was subsequently used as a drug carrier for doxorubicin [DOX] delivery to CaCo-2, colon cancer cells in vitro. DOX was successfully loaded onto CDs-PEG surface confirmed by FT-IR and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer (MALDI-TOF/MS) patterns. The selective treatment of CDs-PEG-DOX against the colorectal cancer cells, , relative to normal human fibroblast cells was succesfully demonstrated.

An insight into the potentials of carbon dots for in vitro live-cell imaging: recent progress, challenges, and prospects

Carbon dots (CDs) are a strong alternative to conventional fluorescent probes for cell imaging due to their brightness, photostability, tunable fluorescence emission, low toxicity, inexpensive preparation, and chemical diversity. Improving the targeting efficiency by modulation of the surface functional groups and understanding the mechanisms of targeted imaging are the most challenging issues in cell imaging by CDs. Firstly, we briefly discuss important features of fluorescent CDs for live-cell imaging application in this review. Then, the newest modulated CDs for targeted live-cell imaging of whole-cell, cell organelles, pH, ions, small molecules, and proteins are elaborately discussed, and their challenges in these fields are explained.

Effects of nitrogen/bismuth-doping on the photocatalyst composite of carbon dots/titanium dioxide nanoparticles (CDs/TNP) for enhanced visible light-driven removal of diclofenac

The present work demonstrates the coupling of titanium dioxide, TiO₂ nanoparticles (TNP) with N-doped, Bi-doped, and N-Bi co-doped rice husk-derived carbon dots (CDs) via a facile dispersion method, forming respective photocatalyst composites of CDs/TNP, N-CDs/TNP, Bi-CDs/TNP and N-Bi-CDs/TNP. Characterization analyzes verified the successful incorporation of respective CDs samples into TNP, forming photocatalyst composite with narrowed band gap and quenched photoluminescence intensity. Photocatalytic activity of TNP and the respective composites was investigated for photodegradation of diclofenac (DCF) under both simulated sunlight and natural sunlight irradiation. The as-prepared N-Bi-CDs/TNP composite showed the best photocatalytic performance among all composites, able to completely degrade 5 ppm of DCF within 60 min and 180 min under both types of visible light irradiation, respectively. The N-Bi-CDs/TNP composite also showed a TOC removal efficiency up to 87.63%. N-Bi-CDs, worked as photosensitizer and electron reservoir, contributed to the outstanding photocatalytic activity of N-Bi-CDs/TNP, whereby the recombination was prolonged and light absorption was shifted towards the visible light region. Furthermore, the composite of N-Bi-CDs/TNP also demonstrated good stability and reusability over repeated degradation cycles. The photodegradation of DCF resulted into several intermediates, which were identified from LC-MS analysis. The present work could provide an insight on the application of heteroatoms doped and co-doped carbon dots in semiconductor oxide as high performance photocatalysts.

Light-activated oxidize-mimicking nanozyme for inhibition of pathogenic Escherichia coli

Here we demonstrate the nanozyme properties of histidine-containing carbon nanodots as externally tunable antibacterial agents through irradiation with visible (VIS) light. The correlative (light and electron) microscopic analysis of treated Escherichia coli O157:H7 revealed that the positive charged carbon nanoparticles might readily adsorb at slightly acid pH on the negative charged cellular envelope of bacteria, and thus, inhibit their growth with over 80% efficiency under illumination with VIS light. The reason was that under VIS irradiation in the range 400-500 nm the adsorbed nanoparticles behaved as effective oxidase-mimicking enzymes and generated reactive oxygen species on the labeled cells. Thus, the light-activated artificial nanozyme caused serious physical damaging of bacterial envelope, which was leading to irreversible cellular inhibition. The outcomes of this study are likely to broaden the scope of designed photoactive carbon nanozymes as powerful antibacterial agents against the emergence of antibiotic and multidrug-resistant strains, as well as proposing of new strategies for infection control.

Current advances in bio-fabricated quantum dots emphasising the study of mechanisms to diversify their catalytic and biomedical applications

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

Preparation of Multifunctional N-Doped Carbon Quantum Dots from Citrus clementina Peel: Investigating Targeted Pharmacological Activities and the Potential Application for Fe3+ Sensing

Carbon quantum dots (CQDs) have recently emerged as innovative theranostic nanomaterials, enabling fast and effective diagnosis and treatment. In this study, a facile hydrothermal approach for N-doped biomass-derived CQDs preparation from Citrus clementina peel and amino acids glycine (Gly) and arginine (Arg) has been presented. The gradual increase in the N-dopant (amino acids) nitrogen content increased the quantum yield of synthesized CQDs. The prepared CQDs exhibited good biocompatibility, stability in aqueous, and high ionic strength media, similar optical properties, while differences were observed regarding the structural and chemical diversity, and biological and antioxidant activity. The antiproliferative effect of CQD@Gly against pancreatic cancer cell lines (CFPAC-1) was observed. At the same time, CQD@Arg has demonstrated the highest quantum yield and antioxidant activity by DPPH scavenging radical method of 81.39 ± 0.39% and has been further used for the ion sensing and cellular imaging of cancer cells. The obtained results have demonstrated selective response toward Fe³⁺ detection, with linear response ranging from 7.0 µmol dm⁻³ to 50.0 µmol dm⁻³ with R² = 0.9931 and limit of detection (LOD) of 4.57 ± 0.27 µmol dm⁻³. This research could be a good example of sustainable biomass waste utilization with potential for biomedical analysis and ion sensing applications.

Recent research progress in the construction of active free radical nanoreactors and their applications in photodynamic therapy

Photodynamic therapy is the most important treatment strategy in free radical therapy. However, tumor microenvironment hypoxia is a key obstacle in PDT. In order to overcome this obstacle, the strategy of in situ production of O₂/radicals by catalytic reaction in solid tumors was proposed. In recent years, it has been found that there are many oxygen-independent carbon-based free radicals that can generate toxic active free radicals under laser irradiation and lead to tumor cell death. Based on the rational design of multifunctional nano-medicine, the active free radical nano-generator has opened up a new way for the highly developed nanotechnology and tumor cooperative therapy to improve the therapeutic effect. In this paper, the research status of active free radical nano-generators, especially reactive oxygen species, including the construction mechanism of active free radical nanomaterials, is reviewed and the application of free radical nano-generators in tumor therapy is emphasized.

Nanomaterials in Photo (Electro) Catalysis

The increasing rate of water and air pollution dramatically impacts natural ecosystems and human health causing depletion of biodiversity, climate changes, spreading of respiratory diseases, and, as a consequence, negatively impacting the world economy [...]

Carbon Dots-Based Logic Gates

Carbon dots (CDs)-based logic gates are smart nanoprobes that can respond to various analytes such as metal cations, anions, amino acids, pesticides, antioxidants, etc. Most of these logic gates are based on fluorescence techniques because they are inexpensive, give an instant response, and highly sensitive. Computations based on molecular logic can lead to advancement in modern science. This review focuses on different logic functions based on the sensing abilities of CDs and their synthesis. We also discuss the sensing mechanism of these logic gates and bring different types of possible logic operations. This review envisions that CDs-based logic gates have a promising future in computing nanodevices. In addition, we cover the advancement in CDs-based logic gates with the focus of understanding the fundamentals of how CDs have the potential for performing various logic functions depending upon their different categories.

Synthesis of Lanthanide-Functionalized Carbon Quantum Dots for Chemical Sensing and Photocatalytic Application

Tunable photoluminescent-functionalized carbon quantum dots CQDs@Ln (TFA)3 (Ln = Eu, Tb; TFA: trifluoroacetylacetone) were designed and synthesized by introducing lanthanide complexes into the modified CQDs surface through the carboxyl group. The as-prepared CQDs@Ln (TFA)3 emit strong blue–green light with the peak at 435 nm and simultaneously show the characteristic emission of Ln3+ under irradiation of 365 nm light in aqueous solution. Moreover, these functionalized CQDs exhibit excellent photoluminescence properties. In addition, a white luminescent solution CQDs@Eu/Tb (TFA)3 was obtained by adjusting the ratio of Eu3+/Tb3+ and the excitation wavelengths. Moreover, CQDs@Tb (TFA)3 can be utilized as a fluorescent probe for the sensitive and selective detection of MnO4− without interference from other ions in aqueous solution. These results provide the meaningful data for the multicomponent assembly and the photoluminescent-functionalized materials based on the modified CQDs and lanthanide, which can be expected to have potential application in photocatalytic or sensors.

N,Fe-Doped Carbon Dot Decorated Gear-Shaped WO3 for Highly Efficient UV-Vis-NIR-Driven Photocatalytic Performance

The development of efficient and non-toxic photocatalysts with a full spectrum response is a primary strategy in the area of photocatalytically mediated pollutant elimination. Herein, we report the preparation of novel nitrogen and iron co-doped carbon dots/gear-shaped WO3 (N,Fe-CDs/G-WO3) with significantly improved broad-spectrum utilization. Characterization results demonstrated that the gear-shaped G-WO3, decorated by N,Fe-CDs with excellent electron transfer/reservoir properties, possessed abundant oxygen vacancies, had large specific surface areas, had multiple light-reflections and had a narrow band gap. As a result, the N,Fe-CDs/G-WO3 composite exhibited excellent photocatalytic activity towards the degradation of water contaminants under full spectrum irradiation. For example, the photodegradative efficiencies of rhodamine B (RhB) reached 81.4%, 97.1%, and 75% in 2 h, under ultraviolet, visible, and near-infrared (UV, vis, and NIR) light irradiation, respectively. Moreover, the N,Fe-CDs/G-WO3 composite also exhibited an outstanding photocatalytic degradation efficiency for other dyes, pharmaceuticals, and personal care products (PPCPs) like methylene blue (MB), ciprofloxacin (CIP), tetracycline hydrochloride (TCH), and oxytetracycline (OTC) (91.1%, 70.5%, 54.5%, and 47.8% in 3 h, respectively). The radical trapping experiments indicated that h+ and ·OH were the main reactive oxidative species (ROS), and the conversion between Fe (III) and Fe (II) played a key role in the photocatalytic reactions. Such a N,Fe-CD decorated material with brilliant photocatalytic activity has tremendous potential for application in environmental remediation.