Carbon dots based FRET for the detection of DNA damage

Fluorescent Molecular Imprinted Sensor Based on Carbon Quantum Dot for Nitrofen Detection in Water Sample

The structure of nitrofen is stable and resistant to natural degradation, persisting in environments for extended periods. It can accumulate through the food chain, posing risks to human health. Here, we report a sensor based on carbon quantum dots (CQDs) and molecular imprinting technology (CQDs@MIPs). It not only possesses the specificity and stability of MIPs but also incorporates the environmental friendliness and signal amplification capabilities of CQDs, making it an ideal material for the specific detection of nitrofen residues in the environment. The interaction between CQDs@MIPs and nitrofen, as well as the successful removal of nitrofen, were confirmed through transmission electron microscopy (TEM) and Zeta potential analysis, which evaluated the morphology and particle size of the prepared CQDs@MIPs. After binding with nitrofen, the CQDs@MIP sensor exhibited a low detection limit (2.5 × 10-3 mg·L-1), a wide detection range (0.01-40 mg·L-1), a good linear relationship (R2 = 0.9951), and a short detection time (5 min). The CQDs@MIP sensor also demonstrated excellent stability, with the fluorescence intensity of CQDs@MIPs remaining above 90% of the initial preparation after 20 days. At the same time, Red, Green, Blue (RGB) color model extraction technology is used to fit the color of the sample under different concentrations, and the smart phone application is integrated to realize the visual detection of nitrofen. Furthermore, acceptable accuracy was achieved in real water samples (recovery rates ranging from 84.1% to 115.7%), indicating that our CQDs@MIP sensor has high analytical potential for real samples.

Ultrasensitive and Selective Nitrogen-Doped Fluorescent Carbon Dots Probe for Quantification Analysis of Trace Cu2+ in the Aqueous Environment

As a typical non-ferrous metal, copper is heavily used in the manufacturing and chemical industries. Copper pollution has been demonstrated to have a significant detrimental impact on the natural environment, as well as causing irreparable damage to the human body, such as elevated Cu2+ levels have been identified as a factor in the pathogenesis of AD (Alzheimer's disease). In this study, novel nanoscale carbon dots Blue-CDs (B-CDs) were obtained by the solvothermal approach in formamide solution utilizing citric acid as the carbon source and ethylenediamine as the nitrogen dopant. The particle size of B-CD was assessed to be 2.17 nm, with a quantum yield (QY) of 10.28%. The B-CDs were found to be extinguished upon exposure to Cu2+, which exhibited a good fluorescence detection linear relationship within the concentration range of 0.25-10.0 µM Cu2+, showing a limit of detection (LOD) is 0.18 µM. B-CDs have been effectively used for the measurement of Cu2+ in actual aqueous systems. It is due to the chemical reactions that take place among the B-CDs and the Cu²⁺ that make the sensor highly sensitivities and highly selectivities. The results of the experiment demonstrate that the fluorescence quenching process is a consequence of Cu2+ binding to the amino groups of carbon dots, forming complexes via a non-radiative photoinduced electron transfer process. In conclusion, the described simple sensing techniques could be effectively utilized as monitoring tools for Cu2+ in environmental waters.

Sustainable Carbon Dots Loaded into Carboxymethylcellulose Based Hydrogels for Uterine Cancer Bioimaging

Background/Objectives: The development of innovative materials for disease diagnostics and therapeutics is a fast-growing area of scientific research. In this work, we report the development of innovative hydrogels incorporating carbon dots (Cdots) for bioimaging purposes. Methods: The Cdots were prepared using a sustainable and low-cost process, starting with an underused fiber from the Brazilian semiarid region. Spectroscopy analysis (Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-visible spectroscopy), X-ray diffraction, photoluminescence, zeta potential, scanning electron microscopy, and transmission electron microscopy were used to characterize these hydrogels. In addition, biocompatibility using the resazurin assay and cellular uptake by confocal microscopy were evaluated. Results: Our results showed that the Cdots changed the structure and crystallinity of hydrogels, mainly due to heat treatment. In addition, hydrogels' chemical groups suffer red and blue shifts following the Cdots incorporation. Moreover, the Cdots were homogeneously incorporated into the hydrogel matrix. Importantly, the cytotoxicity levels were maintained above 90% (p < 0.01), and cellular uptake studies using HeLa cells demonstrated intracellular fluorescence of both the Cdots and hydrogels after incubation. Additionally, the concentration of Cdots within hydrogels significantly affected fluorescence intensity, even compared with pure Cdots. Conclusions: These results showcase the potential for these hydrogels to be further developed as biomarkers and therapeutic biomaterials for women's health.

Prussian blue analogues of Ni-Co-MoS2 nanozymes with high peroxidase like activity for sensitive detection of glyphosate and copper

The rational development of efficient nanozymes for the colorimetric detection of targets is still challenging. Herein, Prussian blue analogues of Ni-Co-MoS2 nano boxes were fabricated for colorimetric detection of glyphosate and copper ions owing to its peroxidase like activity. At the sensing system, the Ni-Co-MoS2 nano boxes display high peroxidase activity, which could catalytically oxidize the colourless TMB to blue colour oxTMB. In presence of glyphosate in this sensing system the blue colour is diminished, ascribed to the inhibit the catalytic activity of Ni-Co-MoS2 nano boxes. Concurrently, the addition of copper ion, which result in blue colour was reappear due to the generation of glyphosate-copper complex formation. The Ni-Co-MoS2 nano boxes based colorimetric sensing platform was developed to sensitive detection of glyphosate and copper ions with low detection limit of 3 nM for glyphosate and 3.8 nM for copper. This method also displays satisfactory outcomes from real samples analysis and its good accuracy. Therefore, this work provides a great potential for rapid detection of the targets from the environments.

Polypyrrole/carbon dot nanocomposite as an electrochemical biosensor for liquid biopsy analysis of tryptophan in the human serum of normal and breast cancer women

Liquid biopsy analysis represents a suitable alternative analysis procedure in several cases where no tumor tissue is available or in poor patient conditions. Amino acids can play a crucial role in aiding cancer diagnosis. Monitoring of tryptophan (Trp) catabolism can aid in tracking cancer progression. Therefore, a novel nanocomposite was fabricated using overoxidized polypyrrole film doped with nano-carbon dots (nano-CDs) on the pencil graphite electrode (PGE) surface for sensitive evaluation of Trp in human serum. Using square wave voltammetry (SWV), the overoxidized polypyrrole/carbon dots/pencil graphite electrode (Ov-Ox PPy/CDs/PGE) achieved excellent electrochemical catalytic activity for evaluating Trp. The modified electrode, known as Ov-Ox PPy/CDs/PGE, demonstrated superior electrochemical catalytic activity compared to bare PGE, CDs/PGE, PPy/PGE, and PPy/CDs/PGE for evaluation of Trp. The method's excellent sensitivity was confirmed by the low limits of detection (LOD = 0.003 μmol L-1) and limit of quantitation (LOQ = 0.009 μmol L-1). The biosensor that was developed can measure tryptophan (Trp) levels in the serum of both healthy individuals and female breast cancer patients with high accuracy and sensitivity. The results indicate that there is a significant difference, as shown by the F-test, between healthy individuals and those with breast cancer. This suggests that Trp amino acid could be an essential biomarker for cancer diagnosis. Consequently, liquid biopsy analysis presents a valuable opportunity for early disease detection, particularly for cancer.

The synthesis of carbon dots by folic acid and utilized as sustainable probe and paper sensor for Hg2+ sensing and cellular imaging

In this work, the blue emission carbon dots (FA-CDs) are synthesized by one-pot solvothermal method by using folic acid as precursor. The FA-CDs emitted bright emission at 445 nm when excited at 360 nm with the QY of 31.2 %. The FA-CDs exhibit sensitive quenching response to Hg²⁺ with variable concentrations systematically, which determined FA-CDs can be employed as fluorescent probe, with a reliable linear relationship between fluorescence intensity and Hg²⁺ concentration, and a limit of detection (LOD) of 1.29 nM. Notably, the quenched FA-CDs can be recovered by using EDTA saturated solution with the emission comparable to initial in succession. The FA-CDs based paper sensor can be explored with similar detection performance, and it can also be restored by EDTA saturated solution. Both the restored CDs and paper sensor can be reused in the next turn for detecting Hg²⁺, which allowed the FA-CDs and their paper sensor can be serviced as sustainable probe for Hg²⁺ detection. The visual LOD of paper sensor can be determined at 0.1 μM, notably, the paper sensor can be reused at least 3 times with good performance, which is beneficial to environmental protection and saving resources. Possess excellent water solubility and non-toxic properties, the cellular imaging of FA-CDs was evaluated with excellent quality fluorescent image results. The FA-CDs provide a promising convenient fluorescent probe for multi-application in detection and imaging.

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.

Phycocyanin - carbon dots nanoprobe for the ratiometric fluorescence determination of peroxynitrite

As a kind of reactive oxygen species, peroxynitrite is related to various diseases closely such as cancer and neurodegenerative diseases. Constructing probes with highly specific ability and a wide linear detection range for peroxynitrite detection is crucial for understanding the pathogenesis of related diseases and optimizing treatments. In this work, we developed a novel luminescent ratiometric fluorescence nanoprobe (PC-CDs) based on carbon dots and phycocyanin. PC-CDs are constructed by amidation reaction between carbon dots and phycocyanin. The nanoprobe we obtained has a good ability of distinguishing peroxynitrite from other reactive oxygen species and interfering substances. Moreover, the linear range of the nanoprobe is 0.5-100 μM and the limit of detection is 0.5 μM when detecting peroxynitrite. In the spiked recovery experiments under phosphate buffered saline (PBS) environment, our nanoprobe has a good recovery performance and the recovery is 99% - 104%, which will be beneficial to the further development of peroxynitrite testing and the research progress of related diseases. Finally, we discuss the quenching mechanism of peroxynitrite for nanoprobe, and found that there is the combination of dynamic and static quenching in the quenching process.

DNA-Mediated Assembly of Carbon Nanomaterials

Carbon nanomaterials (CNMs) have attracted extensive attentions on account of their superior electrical, mechanical, optical, and biological properties. However, the dimensional limit and irregular arrangement have hampered their further application. It is necessary to find an easy, efficient and controllable way to assemble CNMs into well-ordered array. DNA nanotechnology, owning to the advantages of precise programmability, highly structural predictability and spatial addressability, has been widely applied in the assembly of CNMs. Summarizing the progress and achievements in this field will be of great value to related studies. Herein, based on the different dimensions of CNMs containing 0-dimensional (0D) carbon dots (CDs), fullerenes, 1-dimensional (1D) carbon nanotubes (CNTs) and 2-dimensional (2D) graphene, we introduced the conjugation strategies between DNA and CNMs, their different assembly methods and their applications. In addition, we also discuss the existing challenges and future opportunities in the field.

"Off-on" fluorescence probe based on green emissive carbon dots for the determination of Cu2+ ions and glyphosate and development of a smart sensing film for vegetable packaging

An ultra-sensitive glyphosate nanosensor, based on carbon dots (CDs), was successfully developed with excellent long-wavelength emission (530 nm), a high quantum yield (41.3%), and an impressive detection limit (0.8 ng·mL-1). This is the lowest value for glyphosate detection achieved by CD-based fluorescence analysis. The sensor was derived from a separate precursor, 1,4-dihydroxyanthraquinone, and was based on the "off-on" fluorescence analysis, where Cu2+ acts as a dynamic quencher and glyphosate as a fluorescence restorer (excitation wavelength 460 nm). Trace detection of glyphosate is possible with a wide detection range of 50-1300 ng·mL-1 and spiked recoveries between 93.3 and 110.0%. Exploration in depth confirmed that (1) the fluorescence of CDs was derived from the carbon core, (2) the large sp2 conjugated domain consisting of graphitic carbon and nitrogen contributed to the long-wavelength emission, and (3) CDs had an impressive binding interaction with Cu2+, which endow high sensitivity to glyphosate detection. The nanosensor has also be used as a dual-mode visual sensor and a smart sensing membrane that can identify glyphosate on the surface of vegetables, thus showing good practical applicability. Synthetic methods of G-CDs and its detection mechanisms for glyphosate.

Carbon dot composites for bioapplications: a review

Carbon dots (CDs) have received extensive attention in the last decade for their excellent optical, chemical and biological properties. In recent years, CD composites have also received significant attention due to their ability to improve the intrinsic properties and expand the application scope of CDs. In this article, the synthesis processes of four types of CD composites (metal-CD, nonmetallic inorganics-CD, and organics-CD as well as multi-components-CD composites) are systematically summarized first. Then the recent advancements in the bioapplications (bioimaging, drug delivery and biosensing) of these composites are also highlighted and discussed. Last, the current challenges and future trends of CD composites in biomedical fields are discussed.

Intracellular Trafficking of Cationic Carbon Dots in Cancer Cell Lines MCF-7 and HeLa-Time Lapse Microscopy, Concentration-Dependent Uptake, Viability, DNA Damage, and Cell Cycle Profile

Fluorescent carbon dots (CDs) are potential tools for the labeling of cells with many advantages such as photostability, multicolor emission, small size, rapid uptake, biocompatibility, and easy preparation. Affinity towards organelles can be influenced by the surface properties of CDs which affect the interaction with the cell and cytoplasmic distribution. Organelle targeting by carbon dots is promising for anticancer treatment; thus, intracellular trafficking and cytotoxicity of cationic CDs was investigated. Based on our previous study, we used quaternized carbon dots (QCDs) for treatment and monitoring the behavior of two human cancer cell MCF-7 and HeLa lines. We found similarities between human cancer cells and mouse fibroblasts in the case of QCDs uptake. Time lapse microscopy of QCDs-labeled MCF-7 cells showed that cells are dying during the first two hours, faster at lower doses than at higher ones. QCDs at a concentration of 100 µg/mL entered into the nucleus before cellular death; however, at a dose of 200 µg/mL, blebbing of the cellular membrane occurred, with a subsequent penetration of QCDs into the nuclear area. In the case of HeLa cells, the dose-depended effect did not happen; however, the labeled cells were also dying in mitosis and genotoxicity occurred nearly at all doses. Moreover, contrasted intracellular compartments, probably mitochondria, were obvious after 24 h incubation with 100 µg/mL of QCDs. The levels of reactive oxygen species (ROS) slightly increased after 24 h, depending on the concentration, thus the genotoxicity was likely evoked by the nanomaterial. A decrease in viability did not reach IC 50 as the DNA damage was probably partly repaired in the prolonged G0/G1 phase of the cell cycle. Thus, the defects in the G2/M phase may have allowed a damaged cell to enter mitosis and undergo apoptosis. The anticancer effect in both cell lines was manifested mainly through genotoxicity.

Flexible Wearables for Plants

The excellent stretchability and biocompatibility of flexible sensors have inspired an emerging field of plant wearables, which enable intimate contact with the plants to continuously monitor the growth status and localized microclimate in real-time. Plant flexible wearables provide a promising platform for the development of plant phenotype and the construction of intelligent agriculture via monitoring and regulating the critical physiological parameters and microclimate of plants. Here, the emerging applications of plant flexible wearables together with their pros and cons from four aspects, including physiological indicators, surrounding environment, crop quality, and active control of growth, are highlighted. Self-powered energy supply systems and signal transmission mechanisms are also elucidated. Furthermore, the future opportunities and challenges of plant wearables are discussed in detail.

Responsive Carbonized Polymer Dots for Optical Super-resolution and Fluorescence Lifetime Imaging of Nucleic Acids in Living Cells

The rapid development of advanced optical imaging methods including stimulated emission depletion (STED) and fluorescence lifetime imaging microscopy (FLIM) has provided powerful tools for real-time observation of submicrometer biotargets to achieve unprecedented spatial and temporal resolutions. However, the practical imaging qualities are often limited by the performance of fluorescent probes, leading to unsatisfactory results. In particular, long-term imaging of nucleic acids in living cells with STED and FLIM remained desirable yet challenging due to the lack of competent probes combining targeting specificity, biocompatibility, low power requirement, and photostability. In this work, we rationally designed and synthesized a nanosized carbonized polymer dot (CPD) material, CPDs-3, with highly efficient and photostable emission for the super-resolution and fluorescence lifetime imaging of nucleic acids in living cells. The as-fabricated nanoprobe showed responsive emission properties upon binding with nucleic acids, providing an excellent signal-to-noise ratio in both spatial and temporal dimensions. Moreover, the characteristic saturation intensity value of CPDs-3 was as low as 0.68 mW (0.23 MW/cm²), allowing the direct observation of chromatin structures with subdiffraction resolution (90 nm) at very low excitation (<1 μW) and depletion power (<5 mW). Owing to its low toxicity, high photonic efficiency, and outstanding photostability, CPDs-3 was capable of performing long-term imaging both with STED and FLIM setups, demonstrating great potential for the dynamic study of nucleic acid functionalities in the long run.

Recent Advances in Functional Carbon Quantum Dots for Antitumour

Carbon quantum dots (CQDs) are an emerging class of quasi-zero-dimensional photoluminescent nanomaterials with particle sizes less than 10 nm. Owing to their favourable water dispersion, strong chemical inertia, stable optical performance, and good biocompatibility, CQDs have become prominent in biomedical fields. CQDs can be fabricated by “top-down” and “bottom-up” methods, both of which involve oxidation, carbonization, pyrolysis and polymerization. The functions of CQDs include biological imaging, biosensing, drug delivery, gene carrying, antimicrobial performance, photothermal ablation and so on, which enable them to be utilized in antitumour applications. The purpose of this review is to summarize the research progress of CQDs in antitumour applications from preparation and characterization to application prospects. Furthermore, the challenges and opportunities of CQDs are discussed along with future perspectives for precise individual therapy of tumours.

Highly fluorescent carbon dots as novel theranostic agents for biomedical applications

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

Nonenzymatic DNA-Based Fluorescence Biosensor Combining Carbon Dots and Graphene Oxide with Target-Induced DNA Strand Displacement for microRNA Detection

Based on a fluorescence "on-off-on" strategy, we fabricated a simple and highly sensitive DNA-based fluorescence biosensor for the detection of micro (mi)RNA from carbon dots (CDs) and graphene oxide (GO) without complicated and time-consuming operations. CDs were successfully synthesized and conjugated to the end of a single-stranded fuel DNA that was adsorbed onto the surface of GO through π-π stacking, resulting in fluorescence quenching. In the presence of the target miRNA let-7a, the fuel DNA was desorbed from the GO surface, and fluorescence was restored through two successive toehold-mediated strand displacement reactions on double-stranded DNA-modified gold nanoparticles. The target miRNA let-7a was recycled, leading to signal amplification. The concentration of let-7a was proportional to the degree of fluorescence recovery. Under optimal conditions, there was a good linear relationship between the relative fluorescence intensity and let-7a concentration in the range of 0.01-1 nM, with a detection limit of 7.8 pM. With its advantages of signal amplification and high biocompatibility, this fluorescence sensing strategy can be applied to the detection of a variety of target miRNAs and can guide the design of novel biosensors with improved properties.

Förster Resonance Energy Transfer from Carbon Nanoparticles to a DNA-Bound Compound: A Method to Detect the Nature of Binding

A drug molecule can bind in various orientations to a DNA strand. Nature of the binding decides the functionality and efficacy of the drug. To innovate a new method to detect the nature of binding of a drug to DNA strands, herein we have used the dipole-dipole interaction driven Förster resonance energy transfer (FRET) between carbon nanoparticles (CNPs) and a DNA-bound small molecule, (E)-3-ethyl-2-(4-(pyrrolidin-1-yl)styryl)benzo[d]thiazol-3-ium (EPSBT), which belongs to the hemicyanine family and binds typically to the minor groove of a DNA duplex. EPSBT was designed to obtain appreciable fluorescence quantum yield, which constructed an efficient FRET pair with the synthesized CNPs. The tested compound prefers the thymine nucleobase to bind to the DNA strand. Orientation of its dipole on attachment to the DNA strand and the donor-acceptor distance dictate the FRET efficiency with the CNPs. The results provided a precise estimation of the nature of binding of EPSBT to the DNA backbone and, hence, supposedly will help in deciding the functional efficacy.

Nanozymes-Hitting the Biosensing "Target"

Nanozymes are a class of artificial enzymes that have dimensions in the nanometer range and can be composed of simple metal and metal oxide nanoparticles, metal nanoclusters, dots (both quantum and carbon), nanotubes, nanowires, or multiple metal-organic frameworks (MOFs). They exhibit excellent catalytic activities with low cost, high operational robustness, and a stable shelf-life. More importantly, they are amenable to modifications that can change their surface structures and increase the range of their applications. There are three main classes of nanozymes including the peroxidase-like, the oxidase-like, and the antioxidant nanozymes. Each of these classes catalyzes a specific group of reactions. With the development of nanoscience and nanotechnology, the variety of applications for nanozymes in diverse fields has expanded dramatically, with the most popular applications in biosensing. Nanozyme-based novel biosensors have been designed to detect ions, small molecules, nucleic acids, proteins, and cancer cells. The current review focuses on the catalytic mechanism of nanozymes, their application in biosensing, and the identification of future directions for the field.

Synthesis and modification of carbon dots for advanced biosensing application

There has been an explosion of interest in the use of nanomaterials for biosensing applications, and carbonaceous nanomaterials in particular are at the forefront of this explosion. Carbon dots (CDs), a new type of carbon material, have attracted extensive attention due to their fascinating properties, such as small particle size, tunable optical properties, good conductivity, low cytotoxicity, and good biocompatibility. These properties have enabled them to be highly promising candidates for the fabrication of various high-performance biosensors. In this review, we summarize the top-down and bottom-up synthesis routes of CDs, highlight their modification strategies, and discuss their applications in the fields of photoluminescence biosensors, electrochemiluminescence biosensors, chemiluminescence biosensors, electrochemical biosensors and fluorescence biosensors. In addition, the challenges and future prospects of the application of CDs for biosensors are also proposed.

Discriminatory Interaction Behavior of Lipid Vesicles toward Diversely Emissive Carbon Dots Synthesized from Ortho, Meta, and Para Isomeric Carbon Precursors

Photoluminescent carbon dots (C-dots) are widely used for bioimaging techniques to study different cellular processes. However, biocompatibility of C-dots is crucial because the wrong selection of C-dots may lead to an adverse effect on a particular cellular process. Herein, we investigate the interaction of zwitterionic lipid vesicles with photoluminescent C-dots derived from different isomeric (ortho, meta, and para) precursors of phenylenediamine (PDA) by spectroscopic and microscopic imaging techniques as well as dynamic light scattering methods. The study reveals that interaction of lipid vesicles with C-dots is highly dependent on the properties of the isomeric precursors. We find that vesicles retain their morphology upon interaction with ortho C-dots (oCD). The microscopic images reveal that oCD are selectively embedded in the lipid vesicles and can effectively be used for imaging purpose. On the contrary, meta and para C-dots (mCD and pCD) being located on the interfacial region induce aggregation in the vesicles. We explain the observation in terms of the location of the C-dots on the lipid vesicles, their electrostatic attraction at the vesicle interface, possible cross-linking with other vesicles and different hydration features of the isomeric precursors of the C-dots. The study may be helpful in understanding the interactions and attachment processes of C-dots at the interface of biological membranes.

Ultrafast synthesis of carbon quantum dots from fenugreek seeds using microwave plasma enhanced decomposition: application of C-QDs to grow fluorescent protein crystals

Herein, we present the rapid synthesis of mono-dispersed carbon quantum dots (C-QDs) via a single-step microwave plasma-enhanced decomposition (MPED) process. Highly-crystalline C-QDs were synthesized in a matter of 5 min using the fenugreek seeds as a sustainable carbon source. It is the first report, to the best of our knowledge, where C-QDs were synthesized using MPED via natural carbon precursor. Synthesis of C-QDs requires no external temperature other than hydrogen (H2) plasma. Plasma containing the high-energy electrons and activated hydrogen ions predominantly provide the required energy directly into the reaction volume, thus maximizing the atom economy. C-QDs shows excellent Photoluminescence (PL) activity along with the dual-mode of excitation-dependent PL emission (blue and redshift). We investigate the reason behind the dual-mode of excitation-dependent PL. To prove the efficacy of the MPED process, C-QDs were also derived from fenugreek seeds using the traditional synthesis process, highlighting their respective size-distribution, crystallinity, quantum yield, and PL. Notably, C-QDs synthesis via MPED was 97.2% faster than the traditional thermal decomposition process. To the best of our knowledge, the present methodology to synthesize C-QDs via natural source employing MPED is three times faster and far more energy-efficient than reported so far. Additionally, the application of C-QDs to produce the florescent lysozyme protein crystals "hybrid bio-nano crystals" is also discussed. Such a guest-host strategy can be exploited to develop diverse and complex "bio-nano systems". The florescent lysozyme protein crystals could provide a platform for the development of novel next-generation polychrome luminescent crystals.

Phycoremediation potential of microalgae species for ethidium bromide removal from aqueous media

Ethidium Bromide (EtBr) is an organic compound used in molecular biology investigations. EtBr ability of intercalating in the DNA molecule makes it a toxic substance. The objective was to evaluate the phycoremediation potentials of Chlorella vulgaris, Desmodesmus subspicatus and Raphidocelis subcapitata tested separately and in a mixture (Mix) for EtBr removal from the aqueous medium. Experiments were conducted using an initial algae biomass of 10⁶ cell/mL, exposed to 500 µg/L of EtBr. The removal efficiency (µg EtBr L^-1) after 3 h in each treatment were: Mix (72.8 µg.L^-1) >D. subspicatus (48.4 µg.L^-1) >R. subcapitata (24.6 µg.L^-1) >C. vulgaris (19.9 µg.L^-1). However, when EtBr mass reduction per microalgae density is considered (ng.algae^-1), the efficiency ranking changes to: D. subspicatus (1.9 × 10^-5ng.algae^-1) >C. vulgaris (1.4 × 10^-5ng.algae^-1) >Mix (9.8 × 10^-6ng.algae^-1) >R. subcapitata (2.8 × 10^-6ng.algae^-1). The results suggest that initial algal population density is a determinant factor for efficient EtBr removal by microalgae species in short term treatments. In order to obtain 100% of EtBr removal, it should be necessary 10¹⁰, 10¹⁰ and 10¹¹ algae.mL^-1 of C. vulgaris, D. subspicatus and R. subcapitata, respectively. The results strongly suggest phycoremediation can be explored as an alternative method for EtBr removal.

Dual-Response Detection of Oxidized Glutathione, Ascorbic Acid, and Cell Imaging Based on pH/Redox Dual-Sensitive Fluorescent Carbon Dots

The pH/redox dual-sensitive fluorescent carbon dots (pHRCDs) with the fluorescence quantum yield of 16.97% were synthesized by the pyrolysis of l-glutamic acid (l-glu) and dopamine (DA). Compared with the quantum dot (QD)-dopamine conjugate, when the pH value of the solution was changed from neutral to alkaline, the pHRCDs exhibited unique optical phenomenon including red-shift of fluorescence peak and the fluorescence intensity first decreasing from pH 7 to 10 and then increasing from pH 10 to 13. The pHRCDs could be developed for a discriminative and highly sensitive dual-response fluorescent probe for the detection of oxidized glutathione (GSSG) and ascorbic acid (AA) activity in human blood. Under the optimized experimental conditions, the dual-response fluorescent probe can detect GSSG and AA in the linear range of 1.2-3.6 and 27-35 μM with the detection limits of 0.1 and 3.1 μM, respectively. In addition, the pHRCDs demonstrated low cytotoxicity and good biocompatibility, which can be well applied to in vitro cell imaging, and the pHRCDs/GSH fluorescence system has been successfully developed for the detection of AA in real samples.

Real-time and noninvasive detection of UV-Induced deep tissue damage using electrical tattoos

Understanding longterm deep tissue damage caused by UV radiation is imperative for ensuring the health and safety of living organisms that are regularly exposed to radiation sources. While existing UV dosimeters can quantify the cumulative amount of radiation to which an organism is exposed, these sensors cannot reveal the presence and extent of internal tissue damage caused by such exposure. Here we describe a method that uses conducting polymer tattoos to detect UV radiation-induced deep tissue damage in living organisms using bioimpedance analysis (BIA), which allows for noninvasive, real-time measurements of body composition and point-of-care assessment of clinical condition. To establish a performance baseline for this method, we quantify the effects of UVA radiation on live plant leaves. Low-energy UVA waves penetrate further into biological tissue, as compared to UVB, UVC and ionizing radiation, and cause longlasting deep tissue damage that cannot be immediately and readily detected using surface-sensitive techniques, such as photogrammetry and epidermal sensors. We show that single-frequency bioimpedance analysis allows for sensitive, real-time monitoring of UVA damage: as UVA dose increases, the bioimpedance of a plant leaf measured at a frequency of 1 kHz linearly decreases until the extent of radiation damage saturates and the specimen is effectively necrotized. We establish a strong correlation between radiation fluence, internal biological damage and the bioimpedance signal measured using our conducting polymer tattoos, which supports the efficacy of our method as a new type of internal biodosimetry.

Selenium-doped two-photon fluorescent carbon nanodots for in-situ free radical scavenging in mitochondria

Mitochondrial oxidative stress is associated with the occurrence and development of a wide range of human diseases. The development of methodologies to alleviate oxidative stress-mediated injury may have therapeutic potential. Herein, we report the design and preparation of triphenylphosphonium-functionalized selenium-doped carbon nanodots (TPP-Se-CDs) that can efficiently scavenging hydroxyl radicals (OH) and superoxide anions (O₂^-) in mitochondria region. Se-CDs with two-photon blue fluorescence were initially prepared by facile hydrothermal treatment of selenomethionine, followed by the covalent conjugation with TPP. The as-obtained TPP-Se-CDs showed high colloidal stability, strong scavenging abilities towards OH and O₂^-. Moreover, TPP-Se-CDs exhibited low cytotoxicity and mitochondria targeting ability. Taking advantages of these prominent features, TPP-Se-CDs have been successfully applied to combat H₂O₂ and phorbol 12-myristate 13-acetate (PMA) induced oxidative stress in mitochondria.

Fluorescent recognition and selective detection of nitrite ions with carbon quantum dots

The nitrite ion (NO₂^-) is a vital inorganic species that occurs both in natural ecological systems and human bodies. The high concentration of NO₂^- can be harmful for animal and human health. It is important to develop a simple, sensitive, reliable, and economic methodology to precisely monitor NO₂^- in various environmental and biological fields. Thus, a novel nitrite biosensor based on carbon quantum dots (PA-CDs) has been constructed and prepared via a high-efficiency, one-pot hydrothermal route using primary arylamines (PA) such as m-phenylenediamine. The device exhibits bright green fluorescence and a high quantum yield of 20.1% in water. In addition, the PA-CDs also possess two broad linear ranges: 0.05-1.0 μM and 1.0-50 μM with a low detection limit of 7.1 nM. The classical diazo reaction is firstly integrated into the PA-CD system by primary arylamines, which endows the system with high sensitivity and specific selectivity towards nitrite. Importantly, the nanosensor can detect NO₂^- in environmental water and serum samples with high fluorescence recoveries, demonstrating its feasibility in practical applications. This work broadens a new method to fabricate novel nanosensors and provides a prospective application for fluorescent carbon quantum dots (CDs). Graphical abstract.

Carbon dot-based fluorometric optical sensors: an overview

Fluorescent carbon dots (CDs) are a new class of carbon nanomaterials and have demonstrated excellent optical properties, good biocompatibility, great aqueous solubility, low cost, and simple synthesis. Since their discovery, various synthesis methods using different precursors were developed, which were mainly classified as top-down and bottom-up approaches. CDs have presented many applications, and this review article mainly focuses on the development of CD-based fluorescent sensors. The sensing mechanisms, sensor design, and sensing properties to various targets are summarized. Broad ranges of detection, including temperature, pH, DNA, antibiotics, cations, cancer cells, and antibiotics, have been discussed. In addition, the challenges and future directions for CDs as sensing materials are also presented.

Review: immunoassays in DNA damage and instability detection

The review includes information on the current state of knowledge of immunometric methods with emphasis on the possibility of deoxyribonucleic acid (DNA) damage detection. Beginning with basic immunoassay enzyme-linked immunosorbent assay (ELISA), this review describes methods such as tyramide signal amplification (TSA), enhanced polymer one-step staining (EPOS), and time resolved amplified cryptate emission (TRACE) as improvements of ELISA's developed over time to obtain more accurate results. In the second part of the review, surface plasmon resonance (SPR) and quantum dots (QDs) are presented as the newest outlooks in the context of immunoanalysis of biological material and molecular studies. The aim of this review is to briefly present immunoassays with emphasis on DNA damage detection; therefore, the types of methods are listed and described, types of signal indicators, basic definitions such as antigen and antibody are given. Every method is considered with an exemplary application focusing on DNA studies, DNA damage and instability detection.

Two-Step Hydrothermal Preparation of Carbon Dots for Calcium Ion Detection

It is well known that the calcium ion is essential for maintaining life activities in living organisms, and it is of great significance to detect the intracellular calcium concentration. For the detection of calcium ions, we developed a new type of fluorescent carbon dots (CDs), whose surface was modified by ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) through a secondary hydrothermal method. This is a simple and convenient chemical preparation method because all reactions are carried out in the same autoclave, and the final product is directly the EGTA-modified CDs. The CDs exhibit bright blue fluorescence, and as the calcium concentration increases, the fluorescence intensity drops sharply. The fluorescence quenching correlates with the concentration of calcium ions and has a good linearity in the range of 15-300 μM with a detection limit of 0.38 μM. The experimental results confirmed that the detection of calcium ions by CDs is a static fluorescence quenching process. Also, cytotoxicity test and cellular imaging experiments have shown that the CDs are nontoxic and biocompatible.

Nitrogen and Sulfur Doped Carbon Dots from Amino Acids for Potential Biomedical Applications

Nitrogen (N-) and sulfur (S-) doped carbon dots (CDs) were synthesized in a single step in a few min, 1-4 min via microwave technique from five different types of amino acids viz. Arginine (A), Lysine (L), Histidine (H), Cysteine (C), and Methionine (M). These amino acid derived N- and/or S- doped CDs were found to be in spherical shapes with 5-20 nm particle size range determined by Transition Electron Microscope (TEM) images and Dynamic Light Scattering (DLS) measurements. Thermal degradation, functional groups, and surface potential of the CDs were determined by Thermogravimetric Analysis (TGA), FT-IR spectroscopy, and zeta potential measurements, respectively. Although the zeta potential value of Cysteine derived CD (C-CD) was measured as -7.45±1.32 mV, the zeta potential values of A-CD, L-CD, H-CD, and M-CD particles were measured as +2.84±0.67, +2.61±1.0, +4.10±1.50 and+2.20±0.60 mV, respectively. Amongst the CDs, C- CDs was found to possess the highest quantum yield, 89%. Moreover, the blood compatibility test of CDs, determined with hemolysis and blood clotting tests was shown that CDs at 0.25 mg/mL concentration, CDs has less than 5% hemolysis ratio and higher than 50% blood clotting indexes. Furthermore, A-CD was modified with polyethyleneimine (PEI) and was found that the zeta potential values was increased to +34.41±4.17 mV (from +2.84±0.67 mV) inducing antimicrobial capability to these materials. Minimum Inhibition Concentration (MIC) of A-CD dots was found as 2.5 mg/mL whereas the PEI modified A-CDs, A-CD-PEI was found as 1 mg/mL against Escherichia coli ATCC 8739 (gram -) and Staphylococcus aureus ATCC 6538 (gram +) bacteria strains signifying the tunability of CDs.

Rapid synthesis of multifunctional carbon nanodots as effective antioxidants, antibacterial agents, and quercetin nanoprobes

A facile and rapid synthesis of multifunctional carbon nanodots (CNDs) was developed by using the acid-base neutralization spontaneous heat with glucose as precursor, 1,2-ethylenediamine (EDA) and concentrated nitric acid as dual N-dopants. The CND has a tremendous antioxidant potency, which represents effective inhibitory concentrations of reactive oxygen species that are significantly lower than ascorbic acid. Furthermore, minimum inhibitory concentration (MIC) assay revealed CNDs possessed significant antimicrobial activity for Gram-positive S. aureus and Gram-negative E. coli. Moreover, the CNDs are endowed with favorable fluorescence (FL) behaviors including the quantum yield (QY) of 14.2% and stable FL within a wide range of pH and high tolerance to external ionic strength, rendering them applicable in quercetin (QCT) detection as a FL nanoprobe. The CNDs were effectively quenched by QCT due to static quenching which takes place by the electrostatic interaction between basic groups of CNDs and QCT of 3-hydroxyl. This nanoprobe had profitable selectivity and sensitivity towards QCT with a linearity ranging from 1 μM to 47 μM and a low detection limit of 172.4 nM and were successfully performed for QCT detection in human serum and urine samples.

Fluorescent carbon dots based sensing system for detection of enrofloxacin in water solutions

Enrofloxacin (ENR) is one of the environmental pollutants need to remove in many wastewater treatment processes. Traditional methods for measuring ENR are often complex and time-consuming. Due to their low cost and high efficiency, fluorescent carbon dots can be used for detecting many pharmaceuticals. In this contribution, nitrogen doped fluorescent carbon dots (N-CDs) were firstly synthesized with a fluorescence quantum yield of 20.5%. The N-CDs can emit strong blue fluorescence when excited at 368 nm and there exist a large amount of carboxyl, hydroxyl and amine groups on their surfaces. In addition, the fluorescence of N-CDs could be quenched in the presence of Cu²⁺, which could be gradually restored upon adding ENR. Thereby, a rapid and sensitive fluorescent sensing strategy based on the fluorescence recovery of the N-CDs-Cu²⁺ system was designed for selective detection of ENR. The possible sensing mechanism was also proposed in terms of the results of resonance Rayleigh scattering, UV-vis absorption and Fourier transform infrared (FITR) spectra. Under the optimal condition, a good linear relationship was obtained for ENR determination with concentrations ranging from 1.0 to 15.0 μg·mL^-1 and the detection limit of 0.16 μg·mL^-1 was achieved. Finally the proposed sensing system was applied for the detection of ENR in real water samples with satisfactory results.

A carbon dot and gold nanoparticle-based fluorometric immunoassay for 8-hydroxy-2'-deoxyguanosine in oxidatively damaged DNA

A method is described for the fluorometric determination of DNA containing oxidatively damaged product 8-hydroxy-2'-deoxyguanosine (DNA-8-OHdG). Carbon dots (CDs) were modified with glutaraldehyde for DNA conjugation, and antibody against 8-OHdG was immobilized on gold nanoparticles (AuNPs). The presence of DNA-8-OHdG can be linked to CDs by reaction of amino groups on DNA with glutaraldehyde. AuNPs were brought closely to CDs by specific immune reaction between 8-OHdG and antibody on AuNPs. Under 350 nm photoexcitation, the emission of CDs with a peak at 440 nm is quenched by the AuNPs and not restored. In the presence of DNA-8-OHdG, the measured fluorescence intensity decreases and quenching efficiency increases. The limit of detection is 700 pM, and the assay works in the 0.01 nM to 25 μM DNA-8-OHdG concentration range. The method is perceived to possess a good potential as a tool for detecting biomarkers for DNA damage due to oxidative stress. Graphical abstract A fluorometric immunoassay for detecting 8-hydroxy-2'-deoxyguanosine (8-OHdG) in oxidatively damaged DNA is reported. It is based on the use of carbon dots (CDs) and gold nanoparticles (AuNPs). Black wavy lines represent DNA. Yellow polygonal sharps represent 8-OHdG. Blue and pink balls represent CDs and AuNPs, respectively.

Recent development of carbon quantum dots regarding their optical properties, photoluminescence mechanism, and core structure

Carbon quantum dots (CDs) are a relatively new class of carbon nanomaterials which have been studied very much in the last fifteen years to improve their already favorable properties. The optical properties of CDs have drawn particular interest as they display the unusual trait of excitation-dependent emission, as well as high fluorescence quantum yields (QY), long photoluminescence (PL) decay lifetimes, and photostability. These qualities naturally lead researchers to apply CDs in the field of imaging (particularly bio-imaging) and sensing. Since the amount of publications regarding CDs has been growing nearly exponentially in the last ten years, many improvements have been made in the optical properties of CDs such as QY and PL lifetime. However, a great deal of confusion remains regarding the PL mechanism of CDs as well as their structural properties. Therefore, presented in this review is a summary and discussion of the QYs and PL lifetimes reported in recent years. The effect of method as well as precursor has been evaluated and discussed appropriately. The current theories regarding the PL mechanism of CDs are discussed, with special attention to the concept of surface state-controlled PL. With this knowledge, the improvement of preparation and applications of CDs related to their optical properties will be easily accomplished. Further improvements can be made to CDs through the understanding of their structural and optical properties.

A fluorescent biosensor for cardiac biomarker myoglobin detection based on carbon dots and deoxyribonuclease I-aided target recycling signal amplification

A sensitive biosensor using carbon dots and deoxyribonuclease I-aided target recycling signal amplification has been developed to detect myoglobin (MB), which is an important cardiac biomarker and plays a major role in the diagnosis of acute myocardial infarction (AMI). Here, in the absence of MB, the MB aptamer (Ap) is absorbed on the surface of carbon dots (CDs) through π-π stacking interactions, resulting in quenching of the fluorescent label by forming CD-aptamer complexes. Upon adding MB, the Ap sequences could be specifically recognized by MB, leading to the recovery of quenched fluorescence. Thus, quantitative evaluation of MB concentration has been achieved in a broad range from 50 pg mL-1 to 100 ng mL-1, and the detection limit is as low as 20 pg mL-1. This strategy is capable of specific and sensitive detection of MB in human serum, urine, and saliva and can be used for the diagnosis of AMI in the future.

Cannabis sativa-derived carbon dots co-doped with N–S: highly efficient nanosensors for temperature and vitamin B12

Cannabis sativa-derived carbon dots as efficient nanosensors for temperature and vitamin B₁₂.