Full color emitting fluorescent carbon material as reversible pH sensor with multicolor live cell imaging

Harnessing fluorescent carbon quantum dots from natural resource for advancing sweat latent fingerprint recognition with machine learning algorithms for enhanced human identification

Nowadays, it is fascinating to engineer waste biomass into functional valuable nanomaterials. We investigate the production of hetero-atom doped carbon quantum dots (N-S@MCDs) to address the adaptability constraint in green precursors concerning the contents of the green precursors i.e., Tagetes erecta (marigold extract). The successful formation of N-S@MCDs as described has been validated by distinct analytical characterizations. As synthesized N-S@MCDs successfully incorporated on corn-starch powder, providing a nano-carbogenic fingerprint powder composition (N-S@MCDs/corn-starch phosphors). N-S@MCDs imparts astounding color-tunability which enables highly fluorescent fingerprint pattern developed on different non-porous surfaces along with immediate visual enhancement under UV-light, revealing a bright sharp fingerprint, along with long-time preservation of developed fingerprints. The creation and comparison of latent fingerprints (LFPs) are two key research in the recognition and detection of LFPs, respectively. In this work, developed fingerprints are regulated with an artificial intelligence program. The optimum sample has a very high degree of similarity with the standard control, as shown by the program's good matching score (86.94%) for the optimal sample. Hence, our results far outperform the benchmark attained using the conventional method, making the N-S@MCDs/corn-starch phosphors and the digital processing program suitable for use in real-world scenarios.

Red emissive carbon dots: a promising next-generation material with intracellular applicability

The accidental discovery of carbon dots (CDs) back in 2004 has led to their widespread use in the biomedical field. CDs have demonstrated their effectiveness in reporting 3D structures of biological specimens, identifying normal and cancer cells, and even detecting analytes within cells. However, the limitations of blue-green emitting CDs, such as their shallow penetration, photodamage, and auto-fluorescence, have hindered their practical applications. To overcome these limitations, red emissive CDs (RCDs) have been developed, which have deep tissue penetration, minimal photo-damage, low auto-fluorescence, and high imaging contrast. In this article, we present a thorough review on the use of RCDs in biomedical applications, including in vivo and in vitro bioimaging, photoacoustic imaging, monitoring temperature and polarity changes in living cells, tumour therapy, and drug delivery. With the rapid progress being made in the development of RCDs for intracellular applications, their clinical application is expected to become a reality in the near future.

Multifaceted Carbon Dots: toward pH-Responsive Delivery of 5-Fluorouracil for In Vitro Antiproliferative Activity

The synthesis of smart hybrid material to assimilate diagnosis and treatment is crucial in nanomedicine. Herein, we present a simple and facile method to synthesize multitalented blue-emissive nitrogen-doped carbon dots N@PEGCDs. The as-prepared carbon dots N@PEGCDs show enhanced biocompatibility, small size, high fluorescence, and high quantum yield. The N@PEGCDs are used as a drug carrier for 5-fluorouracil (5-FU) with more release at acidic pH. Furthermore, the mode of action of drug-loaded CD (5FU-N@PEGCDs) has also been explored by performing wound healing assay, DCFDA assay for ROS generation, and Hoechst staining. The drug loaded with carbon dots showed less toxicity to normal cells compared to cancer cells, making it a perfect candidate to be studied for designing next-generation drug delivery systems.

What makes carbon nanoparticle a potent material for biological application?

Carbon materials are generally utilized in the form of carbon allotropes and their characteristics are exploited as such or for improving the thermal, electrical, optical, and mechanical properties of other biomaterials. This has now found a broader share in conventional biomaterial space with the generation of nanodiamond, carbon dot, carbon nanoparticles (CNPs), and so forth. With properties of better biocompatibility, intrinsic optical emission, aqueous suspendability, and easier surface conjugation possibilities made CNPs as one of the fore most choice for biological applications especially for use in intracellular spaces. There are various reports available presenting methods of preparing, characterizing, and using CNPs for various biological applications but a collection of information on what makes CNP a suitable biomaterial to achieve those biological activities is yet to be provided in a significant way. Herein, a series of correlations among synthesis, characterization, and mode of utilization of CNP have been incorporated along with the variations in its use as agent for sensing, imaging, and therapy of different diseases or conditions. It is ensembled that how simplified and optimized methods of synthesis is correlated with specific characteristics of CNPs which were found to be suitable in the specific biological applications. These comparisons and correlations among various CNPs, will surely provide a platform to generate new edition of this nanomaterial with improvised applications and newer methods of evaluating structural, physical, and functional properties. This may ensure the eventual use of CNPs for human being for specific need in near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Therapeutic Approaches and Drug Discovery > Emerging Technologies.

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

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

Fluorescent Carbon Dot-Supported Imaging-Based Biomedicine: A Comprehensive Review

Carbon dots (CDs) provide distinctive advantages of strong fluorescence, good photostability, high water solubility, and outstanding biocompatibility, and thus are widely exploited as potential imaging agents for in vitro and in vivo bioimaging. Imaging is absolutely necessary when discovering the structure and function of cells, detecting biomarkers in diagnosis, tracking the progress of ongoing disease, treating various tumors, and monitoring therapeutic efficacy, making it an important approach in modern biomedicine. Numerous investigations of CDs have been intensively studied for utilization in bioimaging-supported medical sciences. However, there is still no article highlighting the potential importance of CD-based bioimaging to support various biomedical applications. Herein, we summarize the development of CDs as fluorescence (FL) nanoprobes with different FL colors for potential bioimaging-based applications in living cells, tissue, and organisms, including the bioimaging of various cell types and targets, bioimaging-supported sensing of metal ions and biomolecules, and FL imaging-guided tumor therapy. Current CD-based microscopic techniques and their advantages are also highlighted. This review discusses the significance of advanced CD-supported imaging-based in vitro and in vivo investigations, suggests the potential of CD-based imaging for biomedicine, and encourages the effective selection and development of superior probes and platforms for further biomedical applications.

Photoactivatable carbon dots as a label-free fluorescent probe for picric acid detection and light-induced bacterial inactivation

The zero-dimensional carbon nanostructure known as carbon dots showed attractive attributes such as multicolour emission, very high quantum yield, up-conversion, very good aqueous solubility, eco-friendliness, and excellent biocompatibility. These outstanding features of the carbon dots have raised significant interest among the research community worldwide. In the current work, water-soluble nitrogen, silver, and gold co-doped bimetallic carbon dots (BCDs) were prepared using the one-pot hydrothermal method with citric acid as a sole carbon source. As prepared BCDs showed size in the range of 4-8 nm and excitation-independent emission behaviour with maximum emission observed at 427 nm. Additionally, these BCDs showed a very high quantum yield value of 50% and fluorescence lifetime value of 10.1 ns respectively. Interestingly, as prepared BCDs selectively sense picric acid (PA) by exhibiting "selective fluorescence turn-off" behaviour in the presence of PA with a limit of detection value (LOD) of 46 nM. Further, as prepared BCDs were explored for photodynamic therapy to inactivate bacterial growth in the presence of light (400-700 nm) by generating singlet oxygen. Thus as prepared BCDs offer lots of potentials to use a nanoprobe to detect picric acid in an aqueous medium and to design next-generation antibacterial materials.

Carbon dots derived from Beta vulgaris: evaluation of its potential as antioxidant and anticancer agent

Carbon dots (CDs) endowed with outstanding physico-chemical characteristics expeditiously garnered tremendous popularity in the scientific community. CDs can be synthesized from a variety of natural resources and can replace metal semiconductor quantum dots in the range of applications such as bio-imaging, sensing and catalysis. Herein, CDs are green synthesized fromBeta vulgarisvia a single step hydrothermal approach (b-CDs). The synthesized carbon dots are characterized using UV-visible spectrophotometry, Fluorescence spectroscopy, High resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction technique (XRD) and Raman spectroscopy. The b-CDs hence developed exhibited the signature 'excitation-dependent fluorescence emission' with its most intense emission in the green region. The quantum yield for the b-CDs obtained by this synthetic approach evinced an appreciable value of 11.6%. The antioxidant property of b-CDs are evaluated using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay to obtain a maximum scavenging activity of 94.5% at a concentration of 1000μg ml^-1and its underlying mechanisms are illustrated. The blood compatibility of b-CDs are assessed using haemolysis assay and the cytotoxicity evaluated using MTT assay shows significant cell growth-inhibition against the human breast cancer (MCF-7) and hepatocellular carcinoma (HepG2) cell lines. This succinct study demonstrates the inherent therapeutic potential of biocompatible carbon dots.

Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

Facile synthesis of N,B-co-doped carbon dots with the gram-scale yield for detection of iron (III) and E. coli

A simple method was developed to prepare fluorescent nitrogen/boron-doped carbon dots (N,B-CDs) in the gram scale. The results showed that the CDs exhibited blue photoluminescence (PL) under 365 nm ultraviolet radiation and excitation-dependent emission. Heteroatoms entered the CDs to enhance the photochemical properties, and their positive properties can be attributed to the presence of guanidino group and functionalized with boronic acid for realizing their utilization in certain applications. These materials could be applied to monitor Fe³⁺ via static PL quenching, yielding a limit of detection (LOD) of 0.74 μM. Furthermore, the charged and boronic acid groups on the prepared N,B-CDs enabled their use as recognition elements to bind with the bacteria through electrostatic interaction and allowed covalent interactions to form the corresponding boronate ester with E. coli (E. coli) bacterial membrane. This method could satisfy a linear range of 10²-10⁷ with LOD of 165 cfu ml^-1 for E. coli. This method was applied for the determination of E. coli in tap water and orange juice samples, and satisfactory results were obtained.

Carbon quantum Dot@Silver nanocomposite-based fluorescent imaging of intracellular superoxide anion

Silver nanoparticle (Ag NP)-coated carbon quantum dot (CQD) core-shell-structured nanocomposites (CQD@Ag NCs) were developed for fluorescent imaging of intracellular superoxide anion (O₂^•-). The morphology of CQD@Ag NCs was investigated by transmission electron microscopy, and the composition was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. CQDs display blue fluorescence with excitation/emission maxima at 360/440 nm, and the fluorescence was quenched by Ag NPs in CQD@Ag NCs. In the presence of O₂^•-, Ag NPs were oxide-etched and the fluorescence of CQDs was recovered. A linearity between the relative fluorescence intensity and O₂^•- solution concentration within the range 0.6 to 1.6 μM was found, with a detection limit of 0.3 μM. Due to their high sensitivity, selectivity, and low cytotoxicity, the as-synthesized CQD@Ag NCs have been successfully applied for imaging of O₂^•- in MCF-7 cells during the whole process of autophagy induced by serum starvation. In our perception, the developed method provides a cost-effective, sensitive, and selective tool in bioimaging and monitoring of intracellular O₂^•- changes, and is promising for potential biological applications. Graphical abstract Illustration of the synthesis of carbon quantum Dot@Silver nanocomposites (CQD@Ag NCs), and CQD@Ag NCs as a "turn-on" nanoprobe for fluorescent imaging of intracellular superoxide anion.

High-quality quantum dots for multiplexed bioimaging: A critical review

Bioimaging done using two or more fluorophores possessing different emission wavelengths can be termed as a multicolor/multiplexed bioimaging technique. Traditionally, images are captured sequentially using multiple fluorophores having specific excitation and emission. For this purpose, multifunctional nanoprobes, such as organic fluorophores, metallic nanoparticles, semiconductor quantum dots, and carbon dots (CDs) are used. Among these fluorophores, quantum dots (QDs) have emerged as an ideal probe for multiplexed bioimaging due to their unique property of size tunable emission. However, the usage of quantum dots in bioimaging is limited due to their toxicity. Furthermore, the reproducibility of optical properties is cynical. These desirable properties, along with enhancement in quantum efficiency, photostability, fluorescence lifetime, etc. can be achieved by stringent control over synthesis parameters. This review summarizes the desirable properties and synthesis methods of such superior QDs followed by their application in multiplexed imaging.

Fluorescent carbon dots driven from ayurvedic medicinal plants for cancer cell imaging and phototherapy

Ayurveda based nanomaterials are recently conceptualized phenomena for biomedical applications especially for imaging and treatment of in vitro cancer cell. Wide range florescent (blue to red emission) quantum dots are versatile materials for imaging and sensing applications. Various procedures and precursors of fluorescent carbon quantum dots (CQDs) are well established and documented in the literature. However, expensive precursors and production, and time consuming process limit their economical design that need to be addressed. Herein, we report a cost effective simple route for fluorescent CQDs by using affordable ayurvedic plant's precursors such as Azadirachta Indica, OcimumTenuiflorum and Tridax Procumbens. Obtained quantum dots from ayurvedic plant leaves namely CQDs-1 (AzadirachtaIndica), CQDs-2 (OcimumTenuiflorum) and CQDs-3 (TridaxProcumbens) showed homogeneous size distribution (∼6–12 nm) and green fluorescent nature, average photo-stability, biocompatibility (more than 85 %), cancer cell imaging and promising phototherapy for cancer and bacterial cell lines.

On-off-on fluorescent carbon dots from waste tea: Their properties, antioxidant and selective detection of CrO42-, Fe3+, ascorbic acid and L-cysteine in real samples

In this work, we reported an economical plant-based hydrothermal method for one-pot green synthesis of water-soluble carbon dots (Tea-CDs) by using waste tea extract as a carbon source. The synthesized Tea-CDs were characterized by UV-visible, fluorescence, FT-IR, TEM, XPS and XRD. The Tea-CDs were found to remove hydroxyl and superoxide anion radical in vitro. In addition, the Tea-CDs exhibited bright blue fluorescence under UV-light (λ_ex = 365 nm), and the fluorescence could be effectively quenched by CrO₄^2- and Fe³⁺ ions. Meanwhile, the fluorescence of Tea-CDs-CrO₄^2- and Tea-CDs-Fe³⁺ systems could be again easily recovered by ascorbic acid (AA) and L-cysteine (L-Cys). As an on-off-on fluorescent nano-sensor of the Tea-CDs, the sensitive detection of CrO₄^2-, Fe³⁺, AA and L-Cys were all performed, showing that the good linear relationships between fluorescence intensity of Tea-CDs and concentration of all testing samples. Finally, the sensors successfully detected CrO₄^2-, Fe³⁺, AA and L-Cys in commercially available real samples with satisfactory recovery ranges. The prepared sensors offer distinct advantages including low cost, simple handling, good sensitivity and high selectivity.

Bioinspired carbon dots: from rose petals to tunable emissive nanodots

Engineering biomass into functional nanomaterials is captivating. The limitation of versatility in green precursors is pursued by exploring the formation of carbon dots with respect to the contents of the green precursor, i.e. Rosa indica. The intermediates formed at different intervals are analyzed. Moreover, the mechanism of heteroatom-doped Rosa indica derived carbon-dot is proposed.

Carbon-based quantum particles: an electroanalytical and biomedical perspective

Carbon-based quantum particles, especially spherical carbon quantum dots (CQDs) and nanosheets like graphene quantum dots (GQDs), are an emerging class of quantum dots with unique properties owing to their quantum confinement effect.

Carbon quantum dots as a fluorophore for “inner filter effect” detection of metronidazole in pharmaceutical preparations

With houttuynia cordata as carbon source, photoluminescent carbon quantum dots (CDs) were obtained via a one-step hydrothermal procedure. The absorption band of metronidazole (MNZ, maximum absorption wavelength at 319 nm) can well overlap with the excitation bands of CDs (maximum excitation wavelength at 320 nm). A fluorescent approach has been developed for detection of MNZ based on the inner filter effect (IFE), in which as-prepared CDs act as an IFE fluorophore and the MNZ as an IFE absorber. We have investigated the mechanism of quenching the fluorescence of CDs and found that the IFE leads to an exponential decay in fluorescence intensity of CDs with increasing concentration of MNZ, but showed a good linear relationship (R² = 0.9930) between ln(F₀/F) with the concentration of MNZ in the range of 3.3 × 10⁻⁶ to 2.4 × 10⁻⁴ mol L⁻¹. Due to the absence of surface modification of the CDs or establishing any covalent linking between the absorber (MNZ) and the fluorophore (CDs), the developed method is simple, rapid, low-cost and less time-consuming. Meanwhile, it possesses a higher sensitivity, wider linear range, and satisfactory selectivity and has potential application for detection of MNZ in pharmaceutical preparations.

CDs were prepared using Houttuynia cordata via hydrothermal process, the absorption band of MNZ can well overlap the excitation bands of CDs, a simple, rapid approach for detection of MNZ was established on the basis of IFE.