Preliminary report on therapeutic potential of coal-derived carbon quantum dots against SARS-CoV-2 virus

Due to the pandemic of COVID-19 and subsequent emerging of new mutant strains, there has been a worldwide hunt for therapeutic and protective agents for its inhibition. In this short communication, for the first time, we report the coal-derived carbon quantum dot (CQD) for the possible therapeutic application against SARS-CoV-2. The synthesized C1-CQD is observed to be safe towards the normal cell line at highest dose, while effectively inhibiting growth of SARS-CoV2 (>95%) with IC50 value of 5.469 μg/mL. Moreover, C1-CQD showed activity against SARS-CoV-2 infection which is comparable to known inhibitory antiviral drug i.e., Remdesivir. These novel findings indicate that coal-based CQDs have highly potent anti-viral activity and could be investigated further for developing cheap and safer alternative therapeutic strategies for inhibition of SARS-CoV-2.

Carbon dots as multifunctional fluorescent probe for Fe3+ sensing in ubiquitous water environments and living cells as well as lysine detection via "on-off-on" mechanism

Iron and amino acids are essential nutrients for living organisms, and their deficiency or excess can cause a range of diseases. Therefore, there is considerable interest in developing sensing assays capable of detecting these nutrients with sensitivity, selectivity, and multifunctionality even in complex environments. In this report, hydrothermally synthesized blue fluorescent carbon dots (C-dots) from zinc gluconate were utilized for the detection of Fe3+ and lysine via "on-off" and "on-off-on" mechanisms, respectively. Specifically, the Fe3+ sensing assay achieved a broad linear range of 0-200 μM and a low limit of detection (LOD) of 1.9 μM. It is worth mentioning that the assay was also well adapted to natural aqueous environments (e.g., lake water), and its linear detection range could be extended to 0-1000 μM with a LOD of 3.3 μM. Furthermore, the assay was also effective for intracellular Fe3+ tracking. Most importantly, the assay could also be applied for the quantitative detection of lysine with a linear range of 0-1200 μM and LOD of 8.6 μM. Systematic mechanistic studies revealed that Fe3+ sensing was based on a static quenching process between C-dots and Fe3+, whereas a stronger complexation might have formed between Fe3+ and Lys, leading to the release of C-dots and thus the recovery of fluorescence.

Effective Detection of Cu(II) Ions Based on Carbon Dots@Exfoliated Layered Double Hydroxides Composites Fluorescence Probe

A series of carbon dots@exfoliated layered double hydroxides (CDs@LDH) composites were hydrothermally fabricated by Mg/Al LDH and formamide. The results of FTIR, UV-vis, and XPS spectra in company with HRTEM images showed that crystalline nano CDs formed on the single layer of LDH by Mg-C bond. With the increase of solvothermal reaction time from 2 to 6 h, the band gap and the binding energy of aminic and graphitic N species of CDs@LDH composites decreased, whereas the crystallinity increased. The fluorescence peaks of CDs@LDH composites could be deconvoluted into short-wavelength (416 nm) and large-wavelength (443 nm) components by Gaussian function, and the fluorescence intensities of both components enhanced with the extension of the solvothermal reaction time. The simultaneous enhancements of fluorescence lifetime and quantum yield resulted from the relatively high electron density in graphitic nitrogen of CDs@LDH, whereas the reduction of nonradiative rate was due to the high crystallinity in the carbon core of CDs@LDH. A strong exciton-lattice interaction also has been validated based on the excitation and emission spectra of CDs@LDH, so the fluorescence emission of CDs@LDH composite was heavily related to its crystalline carbon core and nitrogen-containing groups. CDs@LDH with high nitrogen-containing exhibited a superior detection property for Cu2+ ion sensing with the linear range of 26.90 ~ 192.20 μM and a limit of detection of 0.1957 μM. The photo-induced electron transfer (PET) process dominated the fluorescence quenching of CDs@LDH by Cu2+ ion since the fluorescence lifetime decreased with the increase of Cu2+ ion concentration.

Physicochemical and Inflammatory Analysis of Unconjugated and Conjugated Bone-Binding Carbon Dots

Carbon nanodots (CDs) have drawn significant attention for their potential uses in diagnostic and therapeutic applications due to their small size, tissue biocompatibility, stable photoluminescence, and modifiable surface groups. However, the effect of cargo molecules on CD photoluminescence and their ability to interact with tissues are not fully understood. Our previous work has shown that CDs produced from the acidic oxidation of carbon nanopowder can bind to mineralized bone with high affinity and specificity in a zebrafish animal model system. Using this model, we investigated the impact of loading Cy5 and biotin cargo on CDs' photoluminescence and bone-binding properties. We report that CD cargo loading alters CD photoluminescence in a pH- and cargo-dependent manner without interfering with the CDs' bone binding properties. In a reciprocal analysis, we show that cargo loading of CDs does not affect the cargo's fluorescence. Significantly, CDs do not trigger nitric oxide production in a mouse macrophage assay, suggesting that they are noninflammatory. Together, these results further support the development of carbon nanopowder-derived CDs for the precise delivery of therapeutic agents to bone tissue.

Revolutionizing Cancer Care: Advances in Carbon-Based Materials for Diagnosis and Treatment

Cancer involves intricate pathological mechanisms marked by complexities such as cytotoxicity, drug resistance, stem cell proliferation, and inadequate specificity in current chemotherapy approaches. Cancer therapy has embraced diverse nanomaterials renowned for their unique magnetic, electrical, and optical properties to address these challenges. Despite the expanding corpus of knowledge in this area, there has been less advancement in approving nano drugs for use in clinical settings. Nanotechnology, and more especially the development of intelligent nanomaterials, has had a profound impact on cancer research and treatment in recent years. Due to their large surface area, nanoparticles can adeptly encapsulate diverse compounds. Furthermore, the modification of nanoparticles is achievable through a broad spectrum of bio-based substrates, including DNA, aptamers, RNA, and antibodies. This functionalization substantially enhances their theranostic capabilities. Nanomaterials originating from biological sources outperform their conventionally created counterparts, offering advantages such as reduced toxicity, lower manufacturing costs, and enhanced efficiency. This review uses carbon nanomaterials, including graphene-based materials, carbon nanotubes (CNTs) based nanomaterials, and carbon quantum dots (CQDs), to give a complete overview of various methods used in cancer theranostics. We also discussed their advantages and limitations in cancer diagnosis and treatment settings. Carbon nanomaterials might significantly improve cancer theranostics and pave the way for fresh tumor diagnosis and treatment approaches. More study is needed to determine whether using nano-carriers for targeted medicine delivery may increase material utilization. More insight is required to explore the correlation between heightened cytotoxicity and retention resulting from increased permeability.

All-in-One Photoactivated Inhibition of Butyrylcholinesterase Combined with Luminescence as an Activation and Localization Indicator: Carbon Quantum Dots@Phosphonate Hybrids

Photopharmacology is a booming research area requiring a new generation of agents possessing simultaneous functions of photoswitching and pharmacophore. It is important that any practical implementation of photopharmacology ideally requires spatial control of the medicinal treatment zone. Thus, advances in the study of substances meeting all the listed requirements will lead to breakthrough research in the coming years. In this study, CQDs@phosphonate nanohybrids are presented for the first time and combine biocompatible and nontoxic luminescent carbon quantum dots (CQDs) with photoactive phosphonate enabling inhibition of butyrylcholinesterase (BChE), which is a prognostic marker of numerous diseases. The conjunction of these components in hybrids maintains photoswitching and provides enhancement of BChE inhibition. After laser irradiation with a wavelength of 266 nm, CQDs@phosphonate hybrids demonstrate a drastic increase of butyrylcholinesterase inhibition from 38% up to almost 100% and a simultaneous luminescence decrease. All the listed hybrid properties are demonstrated not only for in vitro experiments but also for complex biological samples, i.e., chicken breast. Thus, the most important achievement is the demonstration of hybrids characterized by a remarkable combination of all-in-one properties important for photopharmacology: (i) bioactivity toward butyrylcholinesterase inhibition, (ii) strong change of inhibition degree as a result of laser irradiation, luminescence as an indicator of (iii) bioactivity state, and of (iv) spatial localization on the surface of a sample.

Carbon Dots for the Treatment of Inflammatory Diseases: An Appraisal of In Vitro and In Vivo Studies

In recent decades, several studies demonstrating various applications of carbon dots (C-dots), including metal sensing, bioimaging, pH sensing, and antimicrobial activities, have been published. Recent developments have shifted this trend toward biomedical applications that target various biomarkers relevant to chronic diseases. However, relevant developments and research results regarding the anti-inflammatory properties of C-dots against inflammation-associated diseases have not been systematically reviewed. Hence, this review discusses the anti-inflammatory effects of C-dots in in vivo and in vitro models of LPS-induced inflammation, gout, cartilage tissue engineering, drug-induced inflammation, spinal cord injury, wound healing, liver diseases, stomach cancer, gastric ulcers, acute kidney and lung injury, psoriasis, fever or hypothermia, and bone tissue regeneration. The compiled studies demonstrate the promising potential of C-dots as anti-inflammatory agents for the development of new drugs.

Understanding the aggregation of excitation wavelength independent emission of amphiphilic carbon dots for bioimaging and organic acid sensing

Herein, excitation wavelength-independent, tunable emissive and amphiphilic CDs with high quantum yield were synthesized by a low-temperature oxidation method employing banana peel waste as a carbon source. These CDs showed longer wavelength emissions (green to yellow) independent of the excitation wavelength when dispersed in different polar to non-polar solvents. The quantum yields of the same CDs were 9-32% in different solvent polarities for different emissions. On the other hand, a large stokes-shifted emission (∼9606 cm^-1) was observed for CDs in the non-polar and weak polar solvents. The particle size of CDs increases from a hydrophobic to a hydrophilic environment with the change in emission colour from yellow to green. A polar and a non-polar host matrix were used to overcome the limitation of aggregation-caused quenching of CDs in the solid state to obtain bright emissions. These CDs were potentially used for naked-eye detection of trifluoroacetic acid (TFA) by changing the emission colour from yellow to orange under UV 365 nm. Sensing of TFA was also shown reversibly switch emission colour and average lifetime for multiple cycles. Additionally, the highly emissive CDs show negligible cytotoxicity in 3T3 fibroblast cells, indicating possible bioimaging applications in 3T3 cells.

Investigation into Red Emission and Its Applications: Solvatochromic N-Doped Red Emissive Carbon Dots with Solvent Polarity Sensing and Solid-State Fluorescent Nanocomposite Thin Films

In this work, a NIR emitting dye, p-toluenesulfonate (IR-813) was explored as a model precursor to develop red emissive carbon dots (813-CD) with solvatochromic behavior with a red-shift observed with increasing solvent polarity. The 813-CDs produced had emission peaks at 610 and 698 nm, respectively, in water with blue shifts of emission as solvent polarity decreased. Subsequently, 813-CD was synthesized with increasing nitrogen content with polyethyleneimine (PEI) to elucidate the change in band gap energy. With increased nitrogen content, the CDs produced emissions as far as 776 nm. Additionally, a CD nanocomposite polyvinylpyrrolidone (PVP) film was synthesized to assess the phenomenon of solid-state fluorescence. Furthermore, the CDs were found to have electrochemical properties to be used as an additive doping agent for PVP film coatings.

A Ratiometric Probe Based on Carbon Dots and Calcein & Eu3+ for the Fluorescent Detection of Sodium Tripolyphosphate

Sodium tripolyphosphate, a food additive, is applied broadly in food industry. However, excessive accumulation of sodium tripolyphosphate can result in electrolyte abnormality of the body. Therefore, it is of great importance to investigate an effective method for the detection of sodium tripolyphosphate. In this work, nitrogen-doped carbon dots (NCDs) with constant fluorescence were fabricated using a domestic microwave oven. A ratiometric fluorescent probe was constructed in which NCDs were as internal standard, calcein & Eu³⁺ were as the detection signal. The fluorescence of calcein at 515 nm was quenched by Eu³⁺, whereas the emission peak of NCDs at 446 nm was almost unchanged. Additionally, the fluorescence of calcein was recovered because of the strong interaction of sodium tripolyphosphate and Eu³⁺. The linear range for sodium tripolyphosphate was 0.5-6 µmol/L with detection limit of 0.12 µmol/L. Furthermore, the ratiometric fluorescent probe was applied for sodium tripolyphosphate detection in real milk samples.

Preparation of Fluorescent Carbon Dots Composites and Their Potential Applications in Biomedicine and Drug Delivery-A Review

Carbon dots (CDs), a new member of carbon nanostructures, rely on surface modification and functionalization for their good fluorescence phosphorescence and excellent physical and chemical properties, including small size (<10 nm), high chemical stability, biocompatibility, non-toxicity, low cost, and easy synthesis. In the field of medical research on cancer (IARC), CDs, a new material with unique optical properties as a photosensitizer, are being applied to heating local apoptosis induction of cancer cells. In addition, imaging tools can also be combined with a drug to form the nanometer complex compound, the imaging guidance for multi-function dosage, so as to improve the efficiency of drug delivery, which also plays a big role in genetic diagnosis. This paper mainly includes three parts: The first part briefly introduces the synthesis and preparation of carbon dots, and summarizes the advantages and disadvantages of different preparation methods; The second part introduces the preparation methods of carbon dot composites. Finally, the application status of carbon dot composites in biomedicine, cancer theranostics, drug delivery, electrochemistry, and photocatalysis is summarized.

Cyclo[18]carbon Formation from C18Br6 and C18(CO)6 Precursors

Although cyclo[18]carbon has been isolated experimentally from two precursors, C₁₈Br₆ and C₁₈(CO)₆, no reaction mechanisms have yet been explored. Herein, we provide insight into the mechanism behind debromination and decarbonylation. Both neutral precursors demonstrate high activation barriers of ∼2.3 eV, while the application of an electric field can lower the barriers by 0.1-0.2 eV. The barrier energy of the anion-radicals is found to be significantly lower for C₁₈Br₆ compared to C₁₈(CO)₆, confirming a considerably higher yield of cylco[18]carbon when the C₁₈Br₆ precursor is used. Elongation of the C-Br bond in the anion-radical confirms its predissociation condition. Natural bonding orbital analysis shows that the stability of C-Br and C-CO bonds in the anion-radicals is lower compared to their neutral species, indicating a possible higher yield. The applied analysis provides crucial details regarding the reaction yield of cyclo[18]carbon and can serve as a general scheme for tuning reaction conditions for other organic precursors.

Sensitive, Selective and Reliable Detection of Fe3+ in Lake Water via Carbon Dots-Based Fluorescence Assay

In this study, C-dots were facilely synthesized via microwave irradiation using citric acid and ethylenediamine as carbon precursors. The fluorescence emissions of the C-dots could be selectively quenched by Fe³⁺, and the degree of quenching was linearly related to the concentrations of Fe³⁺ presented. This phenomenon was utilized to develop a sensitive fluorescence assay for Fe³⁺ detection with broad linear range (0–250, 250–1200 μmol/L) and low detection limit (1.68 μmol/L). Most importantly, the assay demonstrated high reliability towards samples in deionized water, tap water and lake water, which should find potential applications for Fe³⁺ monitoring in complicated environments.

Biowaste-Derived Carbon Dots: A Perspective on Biomedical Potentials

Today, sustainable and natural resources including biowastes have been considered attractive starting materials for the fabrication of biocompatible and biodegradable carbon dots (CDs) due to the benefits of availability, low cost, biorenewability, and environmentally benign attributes. These carbonaceous nanomaterials have been widely explored in the field of sensing/imaging, optoelectronics, photocatalysis, drug/gene delivery, tissue engineering, regenerative medicine, and cancer theranostics. Designing multifunctional biowaste-derived CDs with a high efficacy-to-toxicity ratio for sustained and targeted drug delivery, along with imaging potentials, opens a new window of opportunity toward theranostic applications. However, crucial challenges regarding the absorption/emission wavelength, up-conversion emission/multiphoton fluorescence mechanisms, and phosphorescence of these CDs still need to be addressed to attain the maximum functionality and efficacy. Future studies ought to focus on optimizing the synthesis techniques/conditions, evaluating the influence of nucleation/growth process on structures/properties, controlling their morphology/size, and finding the photoluminescence mechanisms. Reproducibility of synthesis techniques is another critically important factor that needs to be addressed in the future. Herein, the recent developments related to the biowaste-derived CDs with respect to their biomedical applications are deliberated, focusing on important challenges and future perspectives.

Beyond the fluorescence labelling of novel nitrogen-doped silicon quantum dots: the reducing agent and stabilizer for preparing hybrid nanoparticles and antibacterial applications

Silicon quantum dots (SiQDs) have fully demonstrated their applicability in light of their fluorescence. The extension of their applications to other fields, especially considering their excellent biocompatibility, would be more appealing. Herein, a kind of versatile nitrogen-doped silicon quantum dot (N-SiQD) was facilely synthesized via a one-pot hydrothermal method with 3-aminopropyltrimethoxysilane and tetraethylpentylamine as sources. The N-SiQDs were used as a probe for bacterial imaging owing to their good fluorescence properties, stability and biocompatibility. Besides, owing to N doping rendering the N-SiQDs stronger reducibility and Au affinity, the N-SiQDs displayed unique reduction capability, and were attempted as a reducing agent and stabilizer for the synthesis of the nanocomposite, i.e. N-SiQDs stabilized Au nanoparticles (N-SiQDs-AuNPs), under mild conditions. The N-SiQDs-AuNPs showed superior catalytic performance to citric-AuNPs due to the synergistical catalytic effect. In addition, the N-SiQDs exhibited good antibacterial properties against Gram-positive (S. aureus) and Gram-negative bacteria (E. coli) without obvious negative influence on the cells, particularly avoiding the use of any other external stimulation. This study may open a new avenue to use SiQDs for the synthesis of nanocomposites and other biomedicine applications beyond as a fluorescent probe.

Modulation of the binding ability to biomacromolecule, cytotoxicity and cellular imaging property for ionic liquid mediated carbon dots

For the preparation of carbon dots (CDs), a variety of carbon sources and synthetic protocols are available which endow CDs with variable and unpredictable properties. In the present study, three CDs were developed with ionic liquid 1-butyl-3-methylimidazolium dicyanamide as the precursor through ethanol-thermal and hydrothermal strategies, termed as E-CDs and H-CDs, respectively. The features of these carbon dots, i.e., their physicochemical and optical properties, their interactions with bovine serum albumin (BSA) as well as their imaging capability were investigated with respect to the CDs prepared with microwave assisted approach (W-CDs). E-CDs and H-CDs were demonstrated to exhibit similar framework structures and optical properties, and they exhibited larger particle-sizes than that of W-CDs. In addition, the increase of ethanol-thermal and hydrothermal reaction time strengthened the quantum yields of the CDs and promoted their binding capability with BSA. E-CDs and H-CDs showed similar cytotoxicity on normal (LX-2) and cancer (SK-Hep-1) cells. We further found that these CDs may readily enter the cells within 5 min, while the fluorescence of hydrophilic E-CDs and H-CDs was very weak with respect to that of hydrophobic W-CDs in cell imaging. On the other hand, all the CDs exhibited little impact on the level of intracellular reactive oxygen species. The present study is conducive to guide the preparation of suitable carbon dots for different application scenarios.

Recent Advances in Synthesis, Modification, Characterization, and Applications of Carbon Dots

Although there is significant progress in the research of carbon dots (CDs), some challenges such as difficulty in large-scale synthesis, complicated purification, low quantum yield, ambiguity in structure-property correlation, electronic structures, and photophysics are still major obstacles that hinder the commercial use of CDs. Recent advances in synthesis, modification, characterization, and applications of CDs are summarized in this review. We illustrate some examples to correlate process parameters, structures, compositions, properties, and performances of CDs-based materials. The advances in the synthesis approach, purification methods, and modification/doping methods for the synthesis of CDs are also presented. Moreover, some examples of the kilogram-scale fabrication of CDs are given. The properties and performance of CDs can be tuned by some synthesis parameters, such as the incubation time and precursor ratio, the laser pulse width, and the average molar mass of the polymeric precursor. Surface passivation also has a significant influence on the particle sizes of CDs. Moreover, some factors affect the properties and performance of CDs, such as the polarity-sensitive fluorescence effect and concentration-dependent multicolor luminescence, together with the size and surface states of CDs. The synchrotron near-edge X-ray absorption fine structure (NEXAFS) test has been proved to be a useful tool to explore the correlation among structural features, photophysics, and emission performance of CDs. Recent advances of CDs in bioimaging, sensing, therapy, energy, fertilizer, separation, security authentication, food packing, flame retardant, and co-catalyst for environmental remediation applications were reviewed in this article. Furthermore, the roles of CDs, doped CDs, and their composites in these applications were also demonstrated.