Carbon quantum dots and their biomedical and therapeutic applications: a review

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Carbon dots as versatile nanomaterials in sensing and imaging: Efficiency and beyond

Carbon dots (CDs) have emerged as a versatile and promising carbon-based nanomaterial with exceptional optical properties, including tunable emission wavelengths, high quantum yield, and photostability. CDs are appropriate for various applications with many benefits, such as biocompatibility, low toxicity, and simplicity of surface modification. Thanks to their tunable optical properties and great sensitivity, CDs have been used in sensing as fluorescent probes for detecting pH, heavy metal ions, and other analytes. In addition, CDs have demonstrated potential as luminescence converters for white organic light-emitting diodes and light emitters in optoelectronic devices due to their superior optical qualities and exciton-independent emission. CDs have been used for drug administration and bioimaging in the biomedical field due to their biocompatibility, low cytotoxicity, and ease of functionalization. Additionally, due to their stability, efficient charge separation, and low recombination rate, CDs have shown interesting uses in energy systems, such as photocatalysis and energy conversion. This article highlights the growing possibilities and potential of CDs as adaptable nanomaterials in a variety of interdisciplinary areas related to sensing and imaging, at the same time addressing the major challenges involved in the current research and proposing scientific solutions to apply CDs in the development of a super smart society.

Novel Kraft Softwood Lignin-Derived Carbon Quantum Dots: Synthesis, Characterization, and In Vitro Cytocompatibility

Carbon quantum dots (CQDs) have been investigated for biomedical applications in medical imaging due to their fluorescent properties, overall long-term stability, and excellent cytocompatibility and biocompatibility. Lignin is an organic polymer in the tissues of woody plants. It is also considered a byproduct of the wood and pulp industries. Hence, it presents as a renewable source of carbon nanoparticles. In this study, we report the synthesis and material and biological characterization of two colloidal suspensions of CQDs in water derived from lignin-based carbon. One was the native form of CQDs derived from lignin carbon, and the second was doped with nitrogen to evaluate material differences. Material characterization was carried out using various commonly used techniques, including Fourier transform infrared spectroscopy (FTIR), emission and absorbance spectra, zeta potential, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Thin films of CQDs were formed on glass and silicon substrates to assess the in vitro cytocompatibility with human mesenchymal stem cells (hMSCs). Observations suggest that the two forms of CQDs promote cell attachment within 24 h and sustain it for at least 7 days. The overall structure and shape of cells suggest a lack of any adverse or toxic effects of CQDs. The data lay down the novel foundation to support the use of lignin-derived CQDs in tissue engineering applications.

Biomass-derived carbon dots as significant biological tools in the medicinal field: A review

Early disease detection is crucial since it raises the likelihood of treatment and considerably lowers the cost of therapy. Therefore, the improvement of human life and health depends on the development of quick, efficient, and credible biosensing methods. For improving the quality of biosensors, distinct nanostructures have been investigated; among these, carbon dots have gained much interest because of their great performance. Carbon dots, the essential component of fluorescence nanoparticles, having outstanding chemical characteristics, superb biocompatibility, chemical inertness, low toxicity and potential optical characteristics have attracted the researchers from every corner of the globe. Several carbon dots applications have been thoroughly investigated in recent decade, from optoelectronics to biomedical investigations. This review study primarily emphasizes the recent advancements in the field of biomass-derived carbon dots-based drug delivery, gene delivery and bioimaging, and highlights achievements in two major areas: in vivo applications that involve carbon dots absorption in zebrafish and mice, tumour therapeutics, and imaging-guided drug delivery. Additionally, the possible advantages, difficulties, and future possibilities of using carbon dots for biological applications are also explored.

Single-atom nanozymes shines diagnostics of gastrointestinal diseases

Various clinical symptoms of digestive system, such as infectious, inflammatory, and malignant disorders, have a profound impact on the quality of life and overall health of patients. Therefore, the chase for more potent medicines is both highly significant and urgent. Nanozymes, a novel class of nanomaterials, amalgamate the biological properties of nanomaterials with the catalytic activity of enzymes, and have been engineered for various biomedical applications, including complex gastrointestinal diseases (GI). Particularly, because of their distinctive metal coordination structure and ability to maximize atom use efficiency, single-atom nanozymes (SAzymes) with atomically scattered metal centers are becoming a more viable substitute for natural enzymes. Traditional nanozyme design strategies are no longer able to meet the current requirements for efficient and diverse SAzymes design due to the diversification and complexity of preparation processes. As a result, this review emphasizes the design concept and the synthesis strategy of SAzymes, and corresponding bioenzyme-like activities, such as superoxide dismutase (SOD), peroxidase (POD), oxidase (OXD), catalase (CAT), and glutathione peroxidase (GPx). Then the various application of SAzymes in GI illnesses are summarized, which should encourage further research into nanozymes to achieve better application characteristics.

Synthesis of Bio-Base Fluorescence Carbon Dots for Selective Detection of Tartrazine and Sunset Yellow in Food Samples

A green, economical and simple method for the preparation of water-soluble, high-fluorescent carbon quantum dots (CQDs) has been developed via hydrothermal process using pomelo peels as carbon source. The synthesized CQDs were characterized by transmission electron microscopy (TEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR), UV - vis absorption spectra and fluorescence spectrophotometer. The results reveal that the as-prepared C-dots were spherical shape with an average diameter of 2.64 nm and emit bright blue photoluminescence (PL) with a quantum yield of approximately 3.63%. The surface of the C-dots was rich in hydroxyl groups and presented various merits including excellent photostability, low toxicity, and satisfactory solubility. Additionally, we found that two widely used synthetic food colorants, tartrazine and sunset yellow, could result in a strong fluorescence quenching of the C-dots, The possible mechanisms are caused by different ratios of inner filter and static quenching effects. According to this property, This study attempts to establish an analytical method for the determination of tartrazine and sunset yellow using carbon quantum dots as fluorescent probe. A linear relationship was found in the range of 0-100 µM tartrazine and sunset yellow with the detection limit(3σ/k) of 0.65 nM and 1.7 nM. The relative standard deviation (RSD) was 3.5% (tartrazine) and 3.0% (sunset yellow).This observation was further successfully applied for the determination of tartrazine and sunset yellow in food samples collected from local markets, and the recovery rates of the two ranges from 79% to 117.8 and 81 -103.5%, respectively. suggesting its great potential toward food routine analysis.

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.

The discovery of regional neurotoxicity-associated metabolic alterations induced by carbon quantum dots in brain of mice using a spatial metabolomics analysis

BACKGROUND

Recently, carbon quantum dots (CQDs) have been widely used in various fields, especially in the diagnosis and therapy of neurological disorders, due to their excellent prospects. However, the associated inevitable exposure of CQDs to the environment and the public could have serious severe consequences limiting their safe application and sustainable development.

RESULTS

In this study, we found that intranasal treatment of 5 mg/kg BW (20 µL/nose of 0.5 mg/mL) CQDs affected the distribution of multiple metabolites and associated pathways in the brain of mice through the airflow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) technique, which proved effective in discovery has proven to be significantly alerted and research into tissue-specific toxic biomarkers and molecular toxicity analysis. The neurotoxic biomarkers of CQDs identified by MSI analysis mainly contained aminos, lipids and lipid-like molecules which are involved in arginine and proline metabolism, biosynthesis of unsaturated fatty acids, and glutamine and glutamate metabolism, etc. as well as related metabolic enzymes. The levels or expressions of these metabolites and enzymes changed by CQDs in different brain regions would induce neuroinflammation, organelle damage, oxidative stress and multiple programmed cell deaths (PCDs), leading to neurodegeneration, such as Parkinson's disease-like symptoms. This study enlightened risk assessments and interventions of QD-type or carbon-based nanoparticles on the nervous system based on toxic biomarkers regarding region-specific profiling of altered metabolic signatures.

CONCLUSION

These findings provide information to advance knowledge of neurotoxic effects of CQDs and guide their further safety evaluation.

Molecular interactions between gelatin-derived carbon quantum dots and Apo-myoglobin: Implications for carbon nanomaterial frameworks

Carbon nanomaterials (CNMs), including carbon quantum dots (CQDs), have found widespread use in biomedical research due to their low toxicity, chemical tunability, and tailored applications. Yet, there exists a gap in our understanding of the molecular interactions between biomacromolecules and these novel carbon-centered platforms. Using gelatin-derived CQDs as a model CNM, we have examined the impact of this exemplar nanomaterial on apo-myoglobin (apo-Mb), an oxygen-storage protein. Intrinsic fluorescence measurements revealed that the CQDs induced conformational changes in the tertiary structure of native, partially unfolded, and unfolded states of apo-Mb. Titration with CQDs also resulted in significant changes in the secondary structural elements in both native (holo) and apo-Mb, as evidenced by the circular dichroism (CD) analyses. These changes suggested a transition from isolated helices to coiled-coils during the loss of the helical structure of the apo-protein. Infra-red spectroscopic data further underscored the interactions between the CQDs and the amide backbone of apo-myoglobin. Importantly, the CQDs-driven structural perturbations resulted in compromised heme binding to apo-myoglobin and, therefore, potentially can attenuate oxygen storage and diffusion. However, a cytotoxicity assay demonstrated the continued viability of neuroblastoma cells exposed to these carbon nanomaterials. These results, for the first time, provide a molecular roadmap of the interplay between carbon-based nanomaterial frameworks and biomacromolecules.

Recent advances in carbon quantum dots for gene delivery: A comprehensive review

Gene therapy is a revolutionary technology in healthcare that provides novel therapeutic options and has immense potential in addressing genetic illnesses, malignancies, and viral infections. Nevertheless, other obstacles still need to be addressed regarding safety, ethical implications, and technological enhancement. Nanotechnology and gene therapy fields have shown significant promise in transforming medical treatments by improving accuracy, effectiveness, and personalization. This review assesses the possible uses of gene therapy, its obstacles, and future research areas, specifically emphasizing the creative combination of gene therapy and nanotechnology. Nanotechnology is essential for gene delivery as it allows for the development of nano-scale carriers, such as carbon quantum dots (CQDs), which may effectively transport therapeutic genes into specific cells. CQDs exhibit distinctive physicochemical characteristics such as small size, excellent stability, and minimal toxicity, which render them highly favorable for gene therapy applications. The objective of this study is to review and describe the current advancements in the utilization of CQDs for gene delivery. Additionally, it intends to assess existing research, explore novel applications, and identify future opportunities and obstacles. This study offers a thorough summary of the current state and future possibilities of using CQDs for gene delivery. Combining recent research findings highlights the potential of CQDs to revolutionize gene therapy and its delivery methods.

Carbon Dots: A Bright Future as Anticounterfeiting Encoding Agents

Counterfeit products and data vulnerability present significant challenges in contemporary society. Hence, various methods and technologies are explored for anticounterfeiting encoding, with luminescent tracers, particularly luminescent carbon dots (CDs), emerging as a notable solution. CDs offer promising contributions to product security, environmental sustainability, and the circular economy. This critical review aims to highlight the luminescence responsiveness of CDs to physical and chemical stimuli, achieved through nanoengineering their chemical structure. The discussion will delve into the various tunable luminescence mechanisms and decay times of CDs, investigating preferential excitations such as up-conversion, delayed fluorescence, fluorescence, room temperature phosphorescence, persistent luminescence, energy and charge transfer, as well as photo-chemical interactions. These insights are crucial for advancing anticounterfeiting solutions. Following this exploration, a systematic review will focus on the research of luminescent CDs' smart encoding applications, encompassing anticounterfeiting, product tracing, quality certification, and information encryption. Finally, the review will address key challenges in implementing CDs-based technology, providing specific insights into strategies aimed at maximizing their stability and efficacy in anticounterfeiting encoding applications.

Carbon-Based Nanostructures as Emerging Materials for Gene Delivery Applications

Gene therapeutics are promising for treating diseases at the genetic level, with some already validated for clinical use. Recently, nanostructures have emerged for the targeted delivery of genetic material. Nanomaterials, exhibiting advantageous properties such as a high surface-to-volume ratio, biocompatibility, facile functionalization, substantial loading capacity, and tunable physicochemical characteristics, are recognized as non-viral vectors in gene therapy applications. Despite progress, current non-viral vectors exhibit notably low gene delivery efficiency. Progress in nanotechnology is essential to overcome extracellular and intracellular barriers in gene delivery. Specific nanostructures such as carbon nanotubes (CNTs), carbon quantum dots (CQDs), nanodiamonds (NDs), and similar carbon-based structures can accommodate diverse genetic materials such as plasmid DNA (pDNA), messenger RNA (mRNA), small interference RNA (siRNA), micro RNA (miRNA), and antisense oligonucleotides (AONs). To address challenges such as high toxicity and low transfection efficiency, advancements in the features of carbon-based nanostructures (CBNs) are imperative. This overview delves into three types of CBNs employed as vectors in drug/gene delivery systems, encompassing their synthesis methods, properties, and biomedical applications. Ultimately, we present insights into the opportunities and challenges within the captivating realm of gene delivery using CBNs.

Carbon quantum dots in bioimaging and biomedicines

Carbon quantum dots (CQDs) are gaining a lot more attention than traditional semiconductor quantum dots owing to their intrinsic fluorescence property, chemical inertness, biocompatibility, non-toxicity, and simple and inexpensive synthetic route of preparation. These properties allow CQDs to be utilized for a broad range of applications in various fields of scientific research including biomedical sciences, particularly in bioimaging and biomedicines. CQDs are a promising choice for advanced nanomaterials research for bioimaging and biomedicines owing to their unique chemical, physical, and optical properties. CQDs doped with hetero atom, or polymer composite materials are extremely advantageous for biochemical, biological, and biomedical applications since they are easy to prepare, biocompatible, and have beneficial properties. This type of CQD is highly useful in phototherapy, gene therapy, medication delivery, and bioimaging. This review explores the applications of CQDs in bioimaging and biomedicine, highlighting recent advancements and future possibilities to increase interest in their numerous advantages for therapeutic applications.

Nanomaterials for Fluorescent Detection of Hemoglobin

Hemoglobin plays a vital role in a series of biological activities. Abnormal levels of hemoglobin in blood are associated with many clinical diseases. Therefore, development of simple and accurate methods for sensing hemoglobin is of considerable significance. The blowout advancement in nanotechnology has urged the use of different types of fluorescent nanomaterials for hemoglobin assay. The past decades have witnessed the rapid progress of fluorescent nanosensors for hemoglobin assay. In the review, the sensing principles of fluorescent nanomaterials for sensing hemoglobin were briefly discussed. The advances of fluorescent nanosensors for detection of hemoglobin were further highlighted. And the sensing performance of fluorescent nanosensors versus traditional detection approaches was compared. Finally, the challenges and future directions of fluorescent nanomaterials for detection of hemoglobin are discussed. The review will arouse much more attention to the construction of hemoglobin sensors and facilitate rapid development of fluorescent nanosensors of hemoglobin.

A SERS aptasensor based on a flexible substrate for interference-free detection of carbendazim in apple

Non-destructive and interference-free monitoring of pesticide residue on the surface of fruits is still a challenge. Herein, a SERS aptasensor based on a flexible substrate was established for effective carbendazim (CBZ) detection on apple peel. In this sensor, electrospun PVDF/CQDs film served as a flexible supporting substrate. AuNS@Ag was liquid-liquid self-assembled on the PVDF/CQDs film to form a uniform and highly active SERS substrate. During the detection process, aptamers specifically capture the CBZ molecules, while nitrile-mediated Raman tag (MMBN) linked to AuNPs provided optical anti-interference signals. The results showed that the developed sensor had high sensitivity, selectivity, reproducibility, and stability for CBZ detection. Importantly, the flexibility of the SERS substrate helped the sensor realize non-invasive CBZ detection at a concentration as low as 1.20 ng/cm2 on apple peel, which is much lower than the maximum residue limits of CBZ in apples.

Highly Fluorescent ZnO Composite of N-doped Carbon Dots From Dregea Volubilis for Fluorometric Determination of Glucose in Biological Samples

A nano-sensor based on N-doped carbon dots (NCDs)@ZnO (NCZ) composite was fabricated and efficacy for detecting glucose from human blood and urine samples in a straightforward manner was examined. The composite was prepared following a green hydrothermal method under ambient condition using a novel plant material, Dregea volubilis fruit and structural and optical properties were evaluated using standard techniques. The composite exhibited excellent characteristics including good photostability, biocompatibility, low toxicity, and strong fluorescence, with a decent quantum yield of up to 59%. The NCZ composite has been very sensitive and could selectively detect glucose in urine and blood samples. Selective glucose quenching was efficacious at different concentrations of glucose (1-6 mM) and in the pH range of 7-8, limit of detection was 0.25 mM. The potential uses of carbon-based materials have grown, thanks to the excellent sensing/detection capabilities of the NCZ composite as well as the capacity to prevent nanoparticle aggregation, opening up new possibilities for the development of environmentally benign nano-sensors.

Carbon Dots: From Synthesis to Unraveling the Fluorescence Mechanism

Carbon dots (CDs) being a new type of carbon-based nanomaterial have attracted intensive interest from researchers owing to their excellent biophysical properties. CDs are a class of fluorescent carbon nanomaterials that have emerged as a promising alternative to traditional quantum dots and organic dyes in applications including bioimaging, sensing, and optoelectronics. CDs possess unique optical properties, such as tunable emission, facile synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and environmental areas. The synthesis of CDs is achievable by a variety of methods, including bottom-up and top-down approaches, involving the use of different carbon sources and surface functionalization strategies. However, understanding the fluorescence mechanism of CDs remains a challenge. Various mechanistic models have been proposed to explain their origin of luminescence. This review summarizes the recent developments in the synthesis and functionalization of CDs and provides an overview of the current understanding of the fluorescence mechanism.

Synthesis and Application of Carbon Quantum Dots Derived from Carbon Black in Bioimaging

Carbon quantum dots (CQDs) are a new type of fluorescent QDs that consists mainly of carbon atoms. In this research, CQDs were synthesized through harsh oxidizing conditions applied on carbon black and subsequent N-doping using hexamethylenetetramine (Hexamine) and polyethyleneimine (PEI). The synthesized CQDs were characterized using FTIR, AFM, UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, and fluorescence imaging respectively. The AFM images showed that the dots are in the range of 2-8 nm. N-doping of the CQDs increased the PL intensity. The PL enhancement for the CQDs that were N-doped with PEI was higher compared to those N-doped with hexamine. The shift in PL by changing the excitation wavelength has been attributed to the nano-size of the CQDs, functional groups, defect traps, and quantum confinement effect. The in vitro fluorescence imaging revealed that N-doped CQDs can internalize into the cells and be used for fluorescent cell imaging.

Ex Vivo Glucose Detection in Human Blood Serums with Carbon Quantum Dot-Doped Oleic Acid-Treated Chitosan Nanocomposites

Herein, carbon quantum dot (CQD)-doped oleic acid (OL)-treated chitosan (Ch) nanocomposites (Ch-OL/CQD) are prepared by a simple solution technique for nonenzymatic ex vivo detection of glucose in human blood samples. From the architecture of the structure, it is observed that the agglomeration of CQD is restricted by OL-treated Ch polymeric chain, and simultaneously the inhibition in the entanglement of Ch-OL polymeric chains in the matrix is attained by the incorporation of CQD, thereby proving the high stability of the nanocomposite. In vitro detection of glucose is studied by the "Turn ON-OFF" fluorescence technique which is again evidenced by the shining core image of nanocomposites in HRTEM. A highly selective glucose sensing against interfering sugars due to the specific spatial arrangement of the hydroxyl groups of glucose, leading to prominent hydrogen-bonding interaction is established, with a very low limit of detection (LOD) of 1.51 μM, covering a wide linear domain from 0 to 104 μM, R2 = 0.98. Moreover, the calculated glucose levels in real human blood serums by Ch-OL/CQD nanocomposites are compared with a commercial glucometer, with recovery percentages from 95.8 to 107.3%. The clinical potential is supported by studying the stimuli responsiveness of the nanocomposites as a function of pH and ionic strength, encouraging the operation of the sensor in a complex biological scenario. The present work may offer an opportunity for the monitoring of glucose in the blood for successful diabetes management.

Caffeic acid recarbonization: A green chemistry, sustainable carbon nano material platform to intervene in neurodegeneration induced by emerging contaminants

Environmental agents such as pesticides, weedicides and herbicides (collectively referred to as pesticides) are associated with the onset and pathogenesis of neurodegenerative disorders such as Parkinson's (PD) and Alzheimer's (AD) diseases. The development of blood-brain barrier (BBB)-penetrating therapeutic candidates to both prevent and treat the aforementioned xenotoxicant-induced neurodegenerative disorders remains an unmet need. Here, we examine whether caffeic-acid based Carbon Quantum Dots (CACQDs) can intervene in pesticide-associated onset and progress of the PD phenotype. Pulse-chase fluorescence analyses revealed that CACQDs intervene in the soluble-to-toxic transformation of the amyloid-forming protein model Hen Egg White Lysozyme (HEWL). The sp2-rich CACQDs also scavenged free radicals, a milestone along the PD trajectory. In-vitro, CACQDs introduced into a human neuroblastoma-derived cell line (SH-SY5Y) demonstrated negligible cytotoxicity up to 5 mg/mL and protected the cell line against oxidative stress-induced neuronal injury induced by the pesticide and potent neurotoxin, paraquat. Our findings suggest that the potentially BBB-penetrating CACQDs derived from caffeic acid hold promise for mitigating neurodegenerative disorders associated with environmental pesticides and xenobiotic neurotoxicants. Importantly, CACQDs sourced from coffee, coupled with their facile synthesis, represent a sustainable, green chemistry platform for generating interventional candidates in neurodegeneration.

Estimation of Two Diuretics Using Fluorescent Nitrogen Doped Carbon Quantum Dots: Application to Spiked Human Plasma and Tablets

Highly fluorescent nitrogen doped carbon quantum dots (N-CQDs) were prepared by a single-step method based on microwave heating of cane sugar and urea. The produced N-CQDs were applied as nano-sensors for the spectrofluorimetric determination of eplerenone and spironolactone. A strong emission band at 376 nm was obtained after excitation at 216 nm due to the produced N-CQDs. The native fluorescence of N-CQDs was obviously quenched upon adding increased concentrations of each drug. A strong correlation was found between the fluorescence quenching of N-CQDs and the concentration of each drug. The method was found to be linear over the range of 0.5 to 5.0 μg/mL for eplerenone and 0.5 to 6.0 μg/mL for spironolactone with LOQ of 0.383 μg/mL and 0.262 μg/mL. The developed method was further extended for determination of both drugs in their pharmaceutical tablets and spiked human plasma. The results obtained were statistically compared with those of reported methods. The mechanism of fluorescence quenching of N-CQDs by the two drugs was discussed.

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

A novel method for synthesis of carbon dots and their applications in reactive oxygen species (ROS) and glucose detections

A simple and novel method is proposed for preparation of water-soluble fluorescent carbon dots (C-dots), which have potential to be applied in detecting reactive oxygen species (ROS). The C-dots with high fluorescence quantum yield were created by hydrothermal methods with lactose as the carbon source and tris(hydroxylmethyl)aminomethane (Tris) as the surface passivation reagent. The C-dots have some unique characteristics such as excellent biocompatibility with a broad pH working range of 5-11 and high fluorescence, which makes them especially useful in the bio-detection field. The optical properties, surface groups, and element components of the prepared C-dots have been systematically studied by fluorescence spectroscopy. This facile approach is efficient and environmentally friendly and allows large-scale production of the C-dots without any further post-treatment. The C-dots have been adopted as probes for fluorescence turn-off detection owing to their high sensitivity to the hydroxyl radical. The detection limit can reach ∼0.1 μM under optimized conditions when using hydrogen peroxide as the source for generating ROS. Moreover, when paired with glucose oxidase, these C-dots can track glucose concentrations in samples. This adaptability suggests their potential in detecting various metabolites, paving the way for practical uses in disease detection.

Silica-Based Materials Containing Inorganic Red/NIR Emitters and Their Application in Biomedicine

The low absorption of biological substances and living tissues in the red/near-infrared region (therapeutic window) makes luminophores emitting in the range of ~650-1350 nm favorable for in vitro and in vivo imaging. In contrast to commonly used organic dyes, inorganic red/NIR emitters, including ruthenium complexes, quantum dots, lanthanide compounds, and octahedral cluster complexes of molybdenum and tungsten, not only exhibit excellent emission in the desired region but also possess additional functional properties, such as photosensitization of the singlet oxygen generation process, upconversion luminescence, photoactivated effects, and so on. However, despite their outstanding functional applicability, they share the same drawback-instability in aqueous media under physiological conditions, especially without additional modifications. One of the most effective and thus widely used types of modification is incorporation into silica, which is (1) easy to obtain, (2) biocompatible, and (3) non-toxic. In addition, the variety of morphological characteristics, along with simple surface modification, provides room for creativity in the development of various multifunctional diagnostic/therapeutic platforms. In this review, we have highlighted biomedical applications of silica-based materials containing red/NIR-emitting compounds.

Ensemble and single-particle level fluorescent fine-tuning of carbon dots via positional changes of amines toward "supervised" oral microbiome sensing

Significance

Carbon dots (CDs) have attracted a host of research interest in recent years mainly due to their unique photoluminescence (PL) properties that make them applicable in various biomedical areas, such as imaging and image-guided therapy. However, the real mechanism underneath the PL is a subject of wide controversy and can be investigated from various angles.

Aim

Our work investigates the effect of the isomeric nitrogen position as the precursor in the synthesis of CDs by shedding light on their photophysical properties on the single particles and ensemble level.

Approach

To this end, we adopted five isomers of diaminopyridine (DAP) and urea as the precursors and obtained CDs during a hydrothermal process. The various photophysical properties were further investigated in depth by mass spectroscopy. CD molecular frontier orbital analyses aided us in justifying the fluorescence emission profile on the bulk level as well as the charge transfer processes. As a result of the varying fluorescent responses, we indicate that these particles can be utilized for machine learning (ML)-driven sensitive detection of oral microbiota. The sensing results were further supported by density functional theoretical calculations and docking studies.

Results

The generating isomers have a significant effect on the overall photophysical properties at the bulk/ensembled level. On the single-particle level, although some of the photophysical properties such as average intensity remained the same, the overall differences in brightness, photo-blinking frequency, and bleaching time between the five samples were conceived. The various photophysical properties could be explained based on the different chromophores formed during the synthesis. Overall, an array of CDs was demonstrated herein to achieve ∼ 100 % separation efficacy in segregating a mixed oral microbiome culture in a rapid (< 0.5    h ), high-throughput manner with superior accuracy.

Conclusions

We have indicated that the PL properties of CDs can be regulated by the precursors' isomeric position of nitrogen. We emancipated this difference in a rapid method relying on ML algorithms to segregate the dental bacterial species as biosensors.

Neurotoxicological mechanisms of carbon quantum dots in a new animal model Dugesia japonica

As luminescent nanomaterials, the carbon quantum dots (CQDs) research focused on emerging applications since their discovery. However, their toxicological effects on the natural environment are still unclear. The freshwater planarian Dugesia japonica is distributed extensively in aquatic ecosystems and can regenerate a new brain in 5 days after amputation. Therefore it can be used as a new model organism in the field of neuroregeneration toxicology. In our study, D. japonica was cut and incubated in medium treated with CQDs. The results showed that the injured planarian lost the neuronal ability of brain regeneration after treatment with CQDs. Its Hh signalling system was interfered with at Day 5, and all cultured pieces died on or before Day 10 due to head lysis. Our work reveals that CQDs might affect the nerve regeneration of freshwater planarians via the Hh signalling pathway. The results of this study improve our understanding of CQD neuronal development toxicology and can aid in the development of warning systems for aquatic ecosystem damage.

Nitrogen and sulfur co-doped photoluminescent carbon dots for highly selective and sensitive detection of Ag+ and Hg2+ ions in aqueous media: Applications in bioimaging and real sample analysis

In this study, we report the synthesis of photoluminescent (PL) nitrogen (N) and sulfur (S) co-doped carbon dots (NS-CDs) from nitazoxanide and 3-mercaptopropionic acid as a precursors via a one-pot hydrothermal methods. N and S co-doped materials allows more active sites in the CDs surface resulting in an enhancement of their PL properties. NS-CDs show bright blue PL, excellent optical properties, good water solubility, and a high quantum yield (QY) of 32.1%. The as-prepared NS-CDs were confirmed by UV-Visible, photoluminescence, FTIR, XRD and TEM analysis. An optimized excitation at 345 nm, the NS-CDs exhibited strong PL emission at 423 nm with an average size of 3.53 ± 0.25 nm. Under optimized conditions, the NS-CDs PL probe shows high selectivity with Ag⁺/Hg²⁺ ions detected, while other cations no significant changes the PL signal. The PL intensity of NS-CDs linearly quenching and enhancement with Ag⁺ and Hg²⁺ ions from 0 to 50 × 10^-6 M, with the detection limit of 2.15 × 10^-6 M and 6.77 × 10^-7 M (S/N = 3). More interestingly, as-synthesized NS-CDs shows a strong binding to Ag⁺/Hg²⁺ ions with the PL quenching and enhancement to precise and quantitative detection of Ag⁺/Hg²⁺ ions in living cells. The proposed system was effectively utilized for the sensing of Ag⁺/Hg²⁺ ions in real samples resulting in high sensitivity and good recoveries (98.4-109.7%).

Biosynthesis of Quantum Dots and Their Therapeutic Applications in the Diagnosis and Treatment of Cancer and SARS-CoV-2

Quantum dots (QDs) are semiconductor materials that range from 2 nm to 10 nm. These nanomaterials (NMs) are smaller and have more unique properties compared to conventional nanoparticles (NPs). One of the unique properties of QDs is their special optoelectronic properties, making it possible to apply these NMs in bioimaging. Different size and shape QDs, which are used in various fields such as bioimaging, biosensing, cancer therapy, and drug delivery, have so far been produced by chemical methods. However, chemical synthesis provides expensive routes and causes serious environmental and health issues. Therefore, various biological systems such as bacteria, fungi, yeasts, algae, and plants are considered as potent eco-friendly green nanofactories for the biosynthesis of QDs, which are both economic and environmentally safe. The review aims to provide a descriptive overview of the various microbial agents for the synthesis of QDs and their biomedical applications for the diagnosis and treatment of cancer and SARS-CoV-2.

Progress on the luminescence mechanism and application of carbon quantum dots based on biomass synthesis

With the continuous development of carbon-based materials, a variety of new materials have emerged one after another. Carbon Quantum Dots (CQDs) have succeeded in standing out from the crowd of new materials due to their better optical properties in biomedicine, ion detection, anti-counterfeiting materials and photocatalysis. In recent years, through the continuous exploration of CQDs, research scholars have found that the organic substances or heavy metals contained in traditional ones can cause irreversible harm to people and the environment. Therefore, the application of traditional CQDs in future studies will be gradually limited. Among various new materials, biomass raw materials have the merits of good biocompatibility, lower toxicity and green and environmental protection, which largely overcome the defects of traditional materials and have attracted many scholars to focus on the research and development of various biomass CQDs. This paper summarises the optical properties, fluorescence mechanisms, synthetic methods, functionalisation modulation of biomass CQDs and their relevant research progress in the fields of ion detection, bioimaging, biomedicine, biosensing, solar cells, anti-counterfeit materials, photocatalysis and capacitors. Finally, the paper concludes with some discussion of the challenges and prospects of this exciting and promising field of application.

Nanocellulose-Based Passivated-Carbon Quantum Dots (P-CQDs) for Antimicrobial Applications: A Practical Review

Passivated-carbon quantum dots (P-CQDs) have been attracting great interest as an antimicrobial therapy tool due to their bright fluorescence, lack of toxicity, eco-friendly nature, simple synthetic schemes, and possession of photocatalytic functions comparable to those present in traditional nanometric semiconductors. Besides synthetic precursors, CQDs can be synthesized from a plethora of natural resources including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC). Converting MCC into NCC is performed chemically via the top-down route, while synthesizing CODs from NCC can be performed via the bottom-up route. Due to the good surface charge status with the NCC precursor, we focused in this review on synthesizing CQDs from nanocelluloses (MCC and NCC) since they could become a potential source for fabricating carbon quantum dots that are affected by pyrolysis temperature. There are several P-CQDs synthesized with a wide spectrum of featured properties, namely functionalized carbon quantum dots (F-CQDs) and passivated carbon quantum dots (P-CQDs). There are two different important P-CQDs, namely 2,2'-ethylenedioxy-bis-ethylamine (EDA-CQDs) and 3-ethoxypropylamine (EPA-CQDs), that have achieved desirable results in the antiviral therapy field. Since NoV is the most common dangerous cause of nonbacterial, acute gastroenteritis outbreaks worldwide, this review deals with NoV in detail. The surficial charge status (SCS) of the P-CQDs plays an important role in their interactions with NoVs. The EDA-CQDs were found to be more effective than EPA-CQDs in inhibiting the NoV binding. This difference may be attributed to their SCS as well as the virus surface. EDA-CQDs with surficial terminal amino (-NH₂) groups are positively charged at physiological pH (-NH³⁺), whereas EPA-CQDs with surficial terminal methyl groups (-CH₃) are not charged. Since the NoV particles are negatively charged, they are attracted to the positively charged EDA-CQDs, resulting in enhancing the P-CQDs concentration around the virus particles. The carbon nanotubes (CNTs) were found to be comparable to the P-CQDs in the non-specific binding with NoV capsid proteins, through complementary charges, π-π stacking, and/or hydrophobic interactions.

Exploring the multifunctional roles of quantum dots for unlocking the future of biology and medicine

With recent advancements in nanomedicines and their associated research with biological fields, their translation into clinically-applicable products is still below promises. Quantum dots (QDs) have received immense research attention and investment in the four decades since their discovery. We explored the extensive biomedical applications of QDs, viz. Bio-imaging, drug research, drug delivery, immune assays, biosensors, gene therapy, diagnostics, their toxic effects, and bio-compatibility. We unravelled the possibility of using emerging data-driven methodologies (bigdata, artificial intelligence, machine learning, high-throughput experimentation, computational automation) as excellent sources for time, space, and complexity optimization. We also discussed ongoing clinical trials, related challenges, and the technical aspects that should be considered to improve the clinical fate of QDs and promising future research directions.

Surficial amino groups coupling induced concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots via efficient charge transfer

Modification of surficial functional groups among carbon quantum dots (CQDs) has been considered an efficient approach to regulate the fluorescence emission of CQDs. However, the mechanism of how surficial functional groups affect fluorescence is vague which fundamentally limits the further applications of CQDs. Here we report the concentration-dependent fluorescence and fluorescence quantum yield of nitrogen-dopped carbon quantum dots (N-CQDs). At high concentrations (≥0.188 g/L), fluorescence redshift occurs accompanied with decrease in fluorescence quantum yield. Fluorescence excitation spectra and HOMO-LUMO energy gaps calculations show that energy levels of excited states of N-CQDs are relocated via the coupling of surficial amino groups among N-CQDs. Furthermore, electron density difference maps and broadened fluorescence spectra obtained from both experimental measurement and theoretical calculation further confirm that the coupling of surficial amino groups dominates the fluorescence property and verify the formation of charge-transfer state of N-CQDs complex at high concentrations which provides pathways for efficient charge transfer. Given that charge-transfer state induced fluorescence loss and fluorescence spectra broadening are the typical characteristics of organic molecules, CQDs exhibit the optical properties of both quantum dots and organic molecules.

Development of luminescence carbon quantum dots for metal ions detection and photocatalytic degradation of organic dyes from aqueous media

In the present study, fish scale waste was used for the organic synthesis of luminescence CQDs by the hydrothermal method. The impact of CQDs on improved photocatalytic degradation of organic dyes and metal ions detection is examined in this study. The synthesized CQDs had a variety of characteristics that were detected, such as crystallinity, morphology, functional groups, and binding energies. The luminescence CQDs showed outstanding photocatalytic effectiveness for the destruction of methylene blue (96.5%) and reactive red 120 dye (97.8%), respectively after 120 min exposure to visible light (420 nm). The high electron transport properties of the CQDs edges, which make it possible to efficiently separate electron-hole pairs, are attributed to the enhanced photocatalytic activity of the CQDs. These degradation results prove that the CQDs are the outcome of a synergistic interaction between visible light (adsorption); a potential mechanism is also suggested, and the kinetics is analyzed to use a pseudo-first-order model. Additionally, the metal ions detection of CQDs was studied by various metal ions (Hg²⁺, Fe²⁺, Cu²⁺, Ni²⁺, and Cd²⁺) in an aqueous solution and results revealed that the PL intensity of CQDs in presence of cadmium ions decreased. Studies show that the organic fabrication of CQDs are effective photocatalyst and may one day serve as the ideal material to reduce water pollution.

Carbon dots with tissue engineering and regenerative medicine applications

Carbon dots (CDs) with unique physicochemical features such as exceptional biocompatibility, low cost, eco-friendliness, abundant functional groups (e.g., amino, hydroxyl, and carboxyl), high stability, and electron mobility have been broadly investigated in nano- and biomedicine. In addition, the controlled architecture, tunable fluorescence emission/excitation, light-emitting potential, high photostability, high water solubility, low cytotoxicity, and biodegradability make these carbon-based nanomaterials suitable for tissue engineering and regenerative medicine (TE-RM) purposes. However, there are still limited pre- and clinical assessments, because of some important challenges such as the scaffold inconsistency and non-biodegradability in addition to the lack of non-invasive methods to monitor tissue regeneration after implantation. In addition, the eco-friendly synthesis of CDs exhibited some important advantages such as environmentally friendly properties, low cost, and simplicity compared to the conventional synthesis techniques. Several CD-based nanosystems have been designed with stable photoluminescence, high-resolution imaging of live cells, excellent biocompatibility, fluorescence properties, and low cytotoxicity, which make them promising candidates for TE-RM purposes. Combining attractive fluorescence properties, CDs have shown great potential for cell culture and other biomedical applications. Herein, recent advancements and new discoveries of CDs in TE-RM are considered, focusing on challenges and future perspectives.

Synthesis of glutamine-based green emitting carbon quantum dots as a fluorescent nanoprobe for the determination of iron (Fe3+) in Solanum tuberrosum (potato)

Herein, we reported the use of N-doped green-emitting carbon quantum dots (N-CQDs) as a fluorescent probe for determining of Fe³⁺ ions in Solanum tuberosum for the first time. The N-CQDs were synthesised through an efficient, one-step, and safe hydrothermal technique using citric acid as the carbon source and glutamine as a novel nitrogen source. The temporal evolution of the optical properties was investigated by varying the synthetic conditions with respect to temperature (160 °C, 180 °C, 200 °C, 220 °C and 240 °C) and citric acid: glutamine precursor ratio (1:1, 1:1.5, l.2,1:3 and 1:4). The N-CQDs was characterised using Fourier-Transform Infra-red Spectroscopy (FTIR) High-resolution transmission electron microscope (HRTEM), ultraviolet-visible spectroscopy (UV-vis) and X-Ray diffraction analysis (XRD) while its stability was evaluated in different media; NaCl, Roswell Park Memorial Institute (RPMI) and Phosphate Buffered Saline (PBS), and at different pHs. The N-CQDs displayed green (525 nm) emission and were spherical with an average particle diameter of 3.41 ± 0.76 nm. The FTIR indicated carboxylic, amino, and hydroxyl functional groups. The as-synthesised N-CQDs were stable in NaCl (up to 1 M), RPMI, and PBS without any significant change in its fluorescent intensity. The pH evaluation showed pHs 6 and 7 as the optimum pHs, while the fluorometric analysis showed selectivity towards Fe ³⁺ in the presence and absence of interfering ions. The detection limit of 1.05 μM was calculated, and the photoluminescence mechanism revealed static quenching. The as-synthesised N-CQDs was used as a fluorescent nanoprobe to determine the amount of Fe³⁺ in Solanum tuberosum (Potatoes) tubers. The result showed a high level of accuracy (92.13-96.20%) when compared with an established standard analytical procedure with excellent recoveries of 99.23-103.9%. We believe the as-synthesised N-CQDs can be utilised as a reliable and fast fluorescence nanoprobe for the determining of Fe³⁺ ions.

Theranostics Nanomedicine Applications for Colorectal Cancer and Metastasis: Recent Advances

Colorectal cancer (CRC) is the third most common cancer worldwide, and metastatic CRC is a fatal disease. The CRC-affected tissues show several molecular markers that could be used as a fresh strategy to create newer methods of treating the condition. The liver and the peritoneum are where metastasis occurs most frequently. Once the tumor has metastasized to the liver, peritoneal carcinomatosis is frequently regarded as the disease's final stage. However, nearly 50% of CRC patients with peritoneal carcinomatosis do not have liver metastases. New diagnostic and therapeutic approaches must be developed due to the disease's poor response to present treatment choices in advanced stages and the necessity of an accurate diagnosis in the early stages. Many unique and amazing nanomaterials with promise for both diagnosis and treatment may be found in nanotechnology. Numerous nanomaterials and nanoformulations, including carbon nanotubes, dendrimers, liposomes, silica nanoparticles, gold nanoparticles, metal-organic frameworks, core-shell polymeric nano-formulations, and nano-emulsion systems, among others, can be used for targeted anticancer drug delivery and diagnostic purposes in CRC. Theranostic approaches combined with nanomedicine have been proposed as a revolutionary approach to improve CRC detection and treatment. This review highlights recent studies, potential, and challenges for the development of nanoplatforms for the detection and treatment of CRC.

Nanomaterials for fluorescent assay of bilirubin

The accumulation of bilirubin in blood is associated with many diseases. Sensitive and accurate detection of bilirubin is of great significance for personal health care. The rapid development of fluorescent nanomaterials promotes rapid development in the bilirubin assay. In this review, traditional methods for detection of bilirubin are briefly presented to compare with fluorescent nanosensors. Subsequently, the recent progress of different types of fluorescent nanomaterials for determination of bilirubin is summarized. Further, the performance of fluorescent nanosensors and conventional techniques for sensing bilirubin are compared. To this end, the challenges and prospects concerning the topics are discussed. This review will provide some introductory knowledge for researchers to understand the status and importance of fluorescent nanosensors for sensing bilirubin.

Development and application of naturally derived, cost-effective CQDs with cancer targeting potential

Carbon quantum dots (CQDs) derived from natural sources have obtained potential interest in biomedical imaging and therapy because of their excellent biocompatibility properties, which include water solubility, simple synthesis and low cytotoxicity. Here the cytotoxicity of ethylene-diamine doped carbon quantum dots (N-CQDs) delivered to breast cancer MCF-7 cells was investigated. Folic acid was used to raise folate recognition and increase FA-NCQD accumulation in the cells, then apoptosis was assayed using nuclear fragmentation, acridine orange labeling, fluorescence imaging, flow cytometry, and caspase 3 expression. The data show that functionalization of these CQDs, derived from a natural source, have potential application in eliminating cancer cells, as shown here for the invasive breast cancer cells, MCF-7. This nano-delivery system provides a novel target therapy possibility therapeutic approach for cancer cells.

Current trends in carbon-based quantum dots development from solid wastes and their applications

Urbanization and a massive population boom have immensely increased the solid wastes (SWs) generation and are expected to reach 3.40 billion tons by 2050. In many developed and emerging nations, SWs are prevalent in both major and small cities. As a result, in the current context, the reusability of SWs through various applications has taken on added importance. Carbon-based quantum dots (Cb-QDs) and their many variants are synthesized from SWs in a straightforward and practical method. Cb-QDs are a new type of semiconductor that has attracted the interest of researchers due to their wide range of applications, which include everything from energy storage, chemical sensing, to drug delivery. This review is primarily focused on the conversion of SWs into useful materials, which is an essential aspect of waste management for pollution reduction. In this context, the goal of the current review is to investigate the sustainable synthesis routes of carbon quantum dots (CQDs), graphene quantum dots (GQDs), and graphene oxide quantum dots (GOQDs) from various types SWs. The applications of CQDs, GQDs, and GOQDs in the different areas are also been discussed. Finally, the challenges in implementing the existing synthesis methods and future research directions are highlighted.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Fluorescent detection of emerging virus based on nanoparticles: From synthesis to application

The spread of COVID-19 has caused huge economic losses and irreversible social impact. Therefore, to successfully prevent the spread of the virus and solve public health problems, it is urgent to develop detection methods with high sensitivity and accuracy. However, existing detection methods are time-consuming, rely on instruments, and require skilled operators, making rapid detection challenging to implement. Biosensors based on fluorescent nanoparticles have attracted interest in the field of detection because of their advantages, such as high sensitivity, low detection limit, and simple result readout. In this review, we systematically describe the synthesis, intrinsic advantages, and applications of organic dye-doped fluorescent nanoparticles, metal nanoclusters, up-conversion particles, quantum dots, carbon dots, and others for virus detection. Furthermore, future research initiatives are highlighted, including green production of fluorescent nanoparticles with high quantum yield, speedy signal reading by integrating with intelligent information, and error reduction by coupling with numerous fluorescent nanoparticles.

Use of green fluorescent nano-sensors for the determination of furosemide in biological samples and pharmaceutical preparations

BACKGROUND

Carbon quantum dots (CQDs) are new class of carbon nanoparticles. Recently, they have been widely used as fluorescent probes due to their easy accessibility, optical properties and chemical inertness. Many available precursors are used in the synthesis of carbon quantum dots. The electrical and optical properties of CQDs could be enhanced by doping hetero atoms such as nitrogen or sulfur into their structure.

OBJECTIVE

The current work presents the synthesis and characterization of water-soluble nitrogen doped carbon quantum dots (N-CQDs) and their use as fluorescent nano-sensors for the spectrofluorimetric determination of furosemide in its pharmaceutical preparations and spiked human plasma.

METHODS

A domestic microwave was used to prepare the N-CQDs by heating a solution of sucrose and urea till complete charring (about ten minutes). The produced N-CQDs exhibit a strong emission band at 376 nm after excitation at 216 nm. Furosemide caused a quantitative quenching in the fluorescence intensity of the produced N-CQDs.

RESULTS

The proposed method was validated according to ICH Guidelines. The method was found to be linear over the range of 0.1-1.0 µg/mL with LOQ of 0.087 µg/ml.

CONCLUSION

Ecofriendly nano fluorescent sensors (N-CQDs) were successfully synthesized. The size of N-CQDs was distributed in the range of 6.63 nm to 10.23 nm with an average of 8.2 nm. The produced N-CQDs were used as fluorescent probes for the estimation of furosemide in its pharmaceutical preparations as well as spiked human plasma samples.

Facile and Green Synthesis of Novel Fluorescent Carbon Quantum Dots and Their Silver Heterostructure: An In Vitro Anticancer Activity and Imaging on Colorectal Carcinoma

Carbon dots (CQDs) have been widely investigated as prime candidates for developing a tumor theranostic platform due to their tunable fluorescence emission and excitation, high water solubility, good photostability, and biocompatibility. Among the CQDs, natural CQDs are an emerging class of nanomaterials in the carbon family. Herein, highly fluorescent carbon quantum dots (CQDs) were synthesized from orange juice using a one-step hydrothermal method and characterized by different techniques. After that, CQD/Ag heterostructures were synthesized by the reduction of silver salt, in particular silver nitrate (AgNO₃) solution using sodium borohydride (NaBH₄) in different ratios. The photostability and characterization of CQD/Ag heterostructures were investigated. At last, a comparative cellular toxicity measurement was done to select the superior CQD/Ag heterostructure in the human colorectal carcinoma (HCT 116) cell line along with the imaging property. The detailed cell death signaling was also observed in the HCT 116 cell line via the ROS-dependent mitochondrial-mediated pathway, where Akt (RAC-α serine/threonine-protein kinase) played a important role.

A comprehensive model of nitrogen-free ordered carbon quantum dots

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.

Carbon Dots-Based Nanozyme for Drug-Resistant Lung Cancer Therapy by Encapsulated Doxorubicin/siRNA Cocktail

Background

Nanomaterials exhibited intrinsic enzyme-like properties due to the unique properties compared with natural enzyme. Carbon dots (CDs) are an important kind of quantum-sized nanomaterials, which have enormous application potential in bio-imaging, drug carrier, and nanosystems. Carbon dots possess intrinsic enzyme-like properties, such as glutathione (GSH) oxidase or peroxidase activities.

Methods

A co-delivery nanosystem that could carry siRNA and doxorubucin (DOX) simultaneously has been studied in this work. The co-delivery based on carbon dots was surface-modified with poly-ethylenimine (PEI) and loaded the siMRP1 with chemotherapeutics on the surface with pH-triggered drug release. The CD-PEI was synthesized by one-step microwave assisted method; the PEI was raw materials and passivator during the reaction process that makes CDs exhibit excellent optical property.

Results

The CD-PEI was capable of loading and delivering siMRP1 and DOX to tumors and releasing them synchronously in cells in an acid-triggered manner. The particles exhibited GSH oxidase-like catalytic property, oxidizing GSH to oxidized glutathione with concomitant increase of reactive oxygen species (ROS). We found that silencing of MRP1 by co-delivery system antagonized chemoresistance by increasing DOX accumulation and significantly enhancing the inhibitory effect of cell viability induced by CD-PEI-DOX. The co-delivery system dramatically inhibited tumor growth in xenograft model, and CDs counteracted MRP1 function by siRNA-mediated knockdown of MRP1.

Conclusion

Taken together, we uncover the potential role of CDs with a combination of siRNA and chemotherapeutics in overcoming chemoresistance of lung cancer by suppressing MRP1 and oxidation of GSH. Our findings imply its potential of antagonizing chemoresistance to enhance therapeutic efficiency of doxorubicin in clinical practices of lung cancer treatment.