Carbon dots as a fluorescent probe for label-free detection of physiological potassium level in human serum and red blood cells

Fluorescent, phosphorescent, magnetic resonance contrast and radioactive tracer labelling of extracellular vesicles

This review focusses on the significance of fluorescent, phosphorescent labelling and tracking of extracellular vesicles (EVs) for unravelling their biology, pathophysiology, and potential diagnostic and therapeutic uses. Various labeling strategies, such as lipid membrane, surface protein, luminal, nucleic acid, radionuclide, quantum dot labels, and metal complex-based stains, are evaluated for visualizing and characterizing EVs. Direct labelling with fluorescent lipophilic dyes is simple but generally lacks specificity, while surface protein labelling offers selectivity but may affect EV-cell interactions. Luminal and nucleic acid labelling strategies have their own advantages and challenges. Each labelling approach has strengths and weaknesses, which require a suitable probe and technique based on research goals, but new tetranuclear polypyridylruthenium(II) complexes as phosphorescent probes have strong phosphorescence, selective staining, and stability. Future research should prioritize the design of novel fluorescent probes and labelling platforms that can significantly enhance the efficiency, accuracy, and specificity of EV labeling, while preserving their composition and functionality. It is crucial to reduce false positive signals and explore the potential of multimodal imaging techniques to gain comprehensive insights into EVs.

Fluorescence 'turn-off-on' assays for neomycin sulphate and K+ ions with orange-red fluorescent molybdenum nanoclusters

Fluorescent metal nanoclusters (MNCs) have found extensive application in recognizing molecular species. Here, orange-red fluorescent Arg-A. paniculata-MoNCs were synthesized using Andrographis paniculata leaf extract, arginine as a ligand, and MoCl5 as a metal precursor. The Arg-A. paniculata-MoNCs complex exhibited a quantum yield (QY) of 16.91% and excitation/emission wavelengths of 400/665 nm. The synthesized Arg-A. paniculata-MoNCs successfully acted as a probe for assaying neomycin sulphate (NS) via fluorescence turn-off and K+ ions via fluorescence turn-on mechanisms, respectively. Moreover, the developed probe was effectively used to develop a cellulose paper strip-based sensor for detection of NS and K+ ions. Arg-A. paniculata-MoNCs demonstrated great potential for sensing NS and K+ ions, with concentration ranges of 0.1-80 and 0.25-110 μM for NS and K+ ions, respectively. The as-synthesized Arg-A. paniculata-MoNCs efficiently detected NS and K+ ions in food and biofluid samples, respectively.

Multifunctional Gold-Silver-Carbon Quantum Dots Nano-Hybrid Composite: Advancing Antibacterial Wound Healing and Cell Proliferation

The urgent need for innovative materials that effectively eliminate bacteria while promoting cell growth to accelerate wound healing has led to the exploration of new options, as current antimicrobial nanoparticles often exhibit high cytotoxicity, which hinders wound closure. In this study, a nano-hybrid composite, named gold-silver-carbon quantum dots (AuAg-CDs), was prepared by embedding gold and silver nanoclusters into carbon dots. The AuAg-CDs nano-hybrid composite demonstrates remarkable biocompatibility, displays potent antibacterial activity, and possesses a unique capability to promote cell proliferation. By physically disrupting bacterial membranes and promoting mammalian cell proliferation, this composite emerges as a highly promising material for wound healing applications. The underlying mechanism of the multifunctional AuAg-CDs was investigated through comprehensive analyses encompassing cell morphology, bacterial membrane potential, levels of reactive oxygen species (ROS), and adenosine triphosphate (ATP) production in both bacterial and mammalian cells. Additionally, AuAg-CDs were incorporated into alginate to create a hydrogel wound dressing, which underwent evaluation using animal models. The results underscore the remarkable potential of the AuAg-CDs wound dressing in facilitating the proliferation of wound fibroblasts and combating bacterial infections. The significance of designing multifunctional nanomaterials to address the challenges associated with pathogenic bacterial infections and regenerative medicine is highlighted by this study, paving the way for future advancements in these fields.

Effects of plastic-derived carbon dots on germination and growth of pea (Pisum sativum) via seed nano-priming

Seed nano-priming is a promising technology employed in the agronomic field to promote seed germination and plant growth. However, the effects of carbon dots (CDs) on plant development via seed nano-priming remain unclear. In the present study, CDs synthesized from non-biodegradable plastic wastes were adopted as a nano-priming agent for pea (Pisum sativum) seed treatment. The results demonstrated positive effects of seed priming at all CD concentrations (0.25-2 mg/mL), including accelerated seed germination rate, increased shoot and root elongation, biomass accumulation, and root moisture level compared to the control groups. Surface erosion of seed coat was observed after CD priming, which effectively promoted seed imbibition capability. CD penetration, internalization, and translocation were confirmed using transmission electron microscopy. Furthermore, the CD-plant interaction significantly enhanced seed antioxidant enzyme activity, as well as augmented root vigor, chlorophyll content, and carbohydrate content. These findings exhibit great potential of waste-derived CDs as nano-priming agents for seed germination and seedling development in a cost-effective and sustainable manner.

Rapid and sensitifve fluorescence determination of oxytocin using nitrogen-doped carbon dots as fluorophores

In this work, a novel nitrogen (N)-doped carbon dots (N-CDs) was prepared with quercetin as the carbon source and o-phenylenediamine as the nitrogen source by hydrothermal synthesis, and their application as fluorophores for selective and sensitive determination of oxytocin were reported. The fluorescence quantum yield of the as-prepared N-CDs, which exhibited good water solubility and photostability, was about 6.45 % using rhodamine 6 G as reference substance, and the maximum excitation (E_x) and emission (E_m) wavelength were 460 nm and 542 nm, respectively. The results illustrated that the direct fluorescence quenching of N-CDs fluorophore for the detection of oxytocin achieved good linearity in the range of 0.2-5.0 IU/mL and 5.0-10.0 IU/mL, the correlation coefficients were 0.9954 and 0.9909, respectively, and the detection limit was 0.0196 IU/mL (S/N = 3). The recovery rates were 98.8∼103.8 % with RSD= 0.93 %. The interference experiments showed that common metal ions, possible impurities introduced in production and coexisting excipients in the preparation had little adverse influence on selective detection of oxytocin by the developed N-CDs based fluorescent detection method. The mechanism study on the fluorescence quenching of N-CDs by oxytocin concentrations under the given experimental conditions demonstrated that there were internal filtration effect and static quenching in the system. The developed fluorescence analysis platform for the detection of oxytocin had been proved to be rapid, sensitive, specific and accurate, and to be used for the quality inspection of oxytocin.

Quick stabilization of capillary for rapid determination of potassium ions in the blood of epilepsy patients by capillary electrophoresis without sample pretreatment

Mutations in the potassium channel genes may be linked to the development of epilepsy and affect the blood potassium levels. Therefore, accurate determination of potassium in the blood will be critical to diagnose the cause of epilepsy. CE is a competent technique for the fast detection of multiple ions, but complicated matrices of a blood sample may cause significant variation of migration times and the peak shape. In this work, a procedure for rapid stabilization of the capillary inner surface through preflushing of a blood sample was employed. The process takes only 40 min for a capillary and then it can be used for more than 2 weeks. No pretreatment of the blood sample or other surface modification of the capillary is needed for the analysis. The RSDs of the migration time and peak area were reduced to 1.5 and 5.1% from 12.6 and 14.5%, respectively. The proposed method has been successfully applied to the determination of the potassium contents in the blood sample of patients with epilepsy at different stages. The recoveries of potassium ions in these blood samples are in a range from 86.5 to 104.5%.

Band gap tuning and surface modification of carbon dots for sustainable environmental remediation and photocatalytic hydrogen production - A review

Energy and water are the two major issues facing the modern mankind. Providing freshwater requires energy and producing energy uses water. In the present-day scenario, both these routes face growing problems and limitations. Energy crisis has risen due to the depletion of fossil fuels that cause pollution to water bodies making the water unusable for human consumption. In this regard, semiconductor nanocrystals with luminescent properties or carbon quantum dots (CQDs) are the newly developed nanomaterials whose distinctive photo-physical characteristics are focusing to a new generation of robust materials and sensors for sustainable development. In this review, advances in surface and band gap modification of CQDs to improve the activity of nanomaterials will be discussed with special reference to some specific CQDs exhibiting special optical properties for water treatment/splitting applications. Recent advances on CQDs nanocomposites including their applications in photodegradation of organic pollutants, sensing of heavy metal ions in water and water splitting are discussed critically to narrate the future prospects in this field. Challenges and limitations for further improvement are covered to provide smart choices for creating sustainability of benign environment and economic benefits.

Review of Carbon and Graphene Quantum Dots for Sensing

Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluorescent, photoluminescent, chemiluminescent, and electrochemiluminescent properties are what gives them potential in sensing. In this Review, we summarize the basic knowledge on CQDs and GQDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into CQDs- and GQD-based nanomaterials in sensing. With regard to the latter, the authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilize the virtues of these nanomaterials to give us new or better sensors that could not be achieved in other ways.

State-of-the-art: functional fluorescent probes for bioimaging and pharmacological research

Cardiovascular diseases, neuropsychiatric disorders, and cancers seriously endanger human health. Mechanistic and pharmacological mechanisms of candidate drugs are central to the translational paradigm. Since many signal transduction and molecular events are implicated in these diseases, a novel method to interrogate the key pharmacological mechanisms is required to accelerate innovative drug discovery. Much attention now focuses on the real-time visualization of molecular disease events to yield new insights to the pathogenesis of the diseases. This review focuses on recent advances in the development of chemical probes for imaging pathological events to facilitate the study of the underlying pharmacodynamics and toxicity involved. As reviewed here, optical imaging is now frequently viewed as an indispensable technique in the field of biological research. Promoting interdisciplinary collaboration among chemistry, biology and medicine, is necessary to further refine functional fluorescent probes for diagnostic and therapeutic applications.

EDTA-bonded multi-connected carbon-dots and their Eu3+ complex: preparation and optical properties

EDTA-bonded multi-connected carbon-dots (EDTA–C-dots) were prepared from carbon dot precursors and complexed with Eu³⁺ to give Eu³⁺-coordinated EDTA-bonded multi-connected carbon dots (Eu–EDTA–C-dots). Whereas EDTA–C-dots were readily soluble in DMSO, Eu–EDTA–C-dots could not be easily dissolved in DMSO, water, or other common organic solvents. The newly prepared materials were thoroughly characterized. The X-ray diffraction results showed that no crystalline phase of Eu oxides (europium oxide or europium hydroxide) could be observed in Eu–EDTA–C-dots. The infrared and UV-Vis spectra showed that coordination with Eu³⁺ ions did not damage the structure of the EDTA–C-dots. It was found that EDTA could be easily grafted on the surface of carbon dots and EDTA had minimal influence on the photoluminescence of the carbon dot matrix. In contrast, the existence of Eu³⁺ ions strongly quenched the photoluminescence of Eu–EDTA–C-dots. The measured and fitted decay lifetime indicated that Eu–EDTA–C-dots possessed two photoluminescence decay processes, i.e., radiative recombination and non-radiative recombination.

EDTA-bonded multi-connected carbon-dots (EDTA–C-dots) were prepared from carbon dot precursors and complexed with Eu³⁺ to give Eu³⁺-coordinated EDTA-bonded multi-connected carbon dots (Eu–EDTA–C-dots).

Fluorescence turn-on and turn-off sensing of pesticides by carbon dot-based sensor

Green chemistry C-Dot-based ‘turn-on’ and ‘turn-off’ fluorescence sensor for pesticides [imidacloprid (LOD ∼ 0.013 μM) and tetradifon (LOD ∼ 0.04 μM)] in aqueous solution.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

Gold-carbon dots for the intracellular imaging of cancer-derived exosomes

As a novel fluorescent nanomaterial, gold-carbon quantum dots (GCDs) possess high biocompatibility and can be easily synthesized by a microwave-assisted method. Owing to their small sizes and unique optical properties, GCDs can be applied to imaging of biological targets, such as cells, exosomes and other organelles. In this study, GCDs were used for fluorescence imaging of exosomes. Tumor-specific antibodies are attached to the GCDs, forming exosome specific nanoprobes. The nanoprobes can label exosomes via immuno-reactions and thus facilitate fluorescent imaging of exosomes. When incubated with live cells, exosomes labeled with the nanoprobes can be taken up by the cells. The intracellular experiments confirmed that the majority of exosomes were endocytosed by cells and transported to lysosomes. The manner by which exosomes were taken up and the intracellular distribution of exosomes are unaffected by the GCDs. The experimental results successfully demonstrated that the presented nanoprobe can be used to study the intrinsic intracellular behavior of tumor derived exosomes. We believe that the GCDs based nanoprobe holds a great promise in the study of exosome related cellular events, such as cancer metastasis.

Incorporation of surface plasmon resonance with novel valinomycin doped chitosan-graphene oxide thin film for sensing potassium ion

In this study, the combination of novel valinomycin doped chitosan-graphene oxide (C-GO-V) thin film and surface plasmon resonance (SPR) system for potassium ion (K⁺) detection has been developed. The novel C-GO-V thin film was deposited on the gold surface using spin coating technique. The system was used to monitor SPR signal for K⁺ in solution with and without C-GO-V thin film. The K⁺ can be detected by measuring the SPR signal when C-GO-V thin film is exposed to K⁺ in solution. The sensor produces a linear response for K⁺ ion up to 100ppm with sensitivity and detection limit of 0.00948°ppm^-1 and 0.001ppm, respectively. These results indicate that the C-GO-V film is high potential as a sensor element for K⁺ that has been proved by the SPR measurement.

“Off–On” fluorescent sensing of organophosphate pesticides using a carbon dot–Au(iii) complex

Herein, we report novel “off–on” fluorescent sensing of organophosphate pesticides using a carbon dot (CD)–Au(iii) complex/acetylcholinesterase (AChE) system.

A green emissive carbon-dot-based sensor with diverse responsive manners for multi-mode sensing

Multi-mode sensing for Hg²⁺, lemon yellow, H₂O₂ and Fe²⁺ achieved by a green emissive carbon-dot-based sensor with diverse responsive manners.

Tetraphenylethene derivative modified DNA oligonucleotide for in situ potassium ion detection and imaging in living cells

The monitoring of K⁺ is very important and emergency because of their unique relationship in various disease diagnosis and treatment. G-quadruplex analogue is a classical recognition unit for K⁺ detection and has been widely applied in K⁺ relevant research. Common fluorescent dyes were employed for design of G-quadruplex structure-based K⁺ probes which suffered from the aggregation-caused quenching effect, and possibly limited the biological applications in living systems. Herein, we report an aggregation-induced emission (AIE) effect-based fluorescent probe for cellular K⁺ analysis and imaging. Benefitting from the K⁺ triggered AIE phenomenon, the designed TPE derivative modified guanine (G)-rich oligonucleotide fluorescent probe (TPE-oligonucleotide probe) exhibits high sensitivity (∼10-fold higher than most reported G-quadruplex-based probes) with extended photostability which facilitates the prolonged fluorescence observations of K⁺ in living cells. On the basis of these advantages, the TPE-oligonucleotide probe serves as a promising candidate for the functional study and analysis of K⁺.

A membrane-anchored fluorescent probe for detecting K(+) in the cell microenvironment

Cell-surface fluorescent probes are effective tools in cell biology and engineering. Here, we for the first time report a diacyllipid-aptamer conjugate-based fluorescent probe which could anchor on cell membrane for real-time tracking of potassium ions in the cell microenvironment.

New development in carbon quantum dots technical applications

As a newly emerged member in carbon nanomaterials family, carbon quantum dots (CQDs) attracted everincreasing attention owing to their ultracompact size, excellent photoluminescence, favorable biocompatibility, versatile surface and superior electron transfer ability. The past decade has witnessed continuous advancements in the production of CQDs with high photoluminescence quantum yields for various applications. Herein, we track the newest development of CQDs with advanced physicochemical properties and their applications in sensing, bioimaging, nanomedicine and catalysis, and propose the challenges and perspectives in this exciting and promising field.

Preparation of Gold-Carbon Dots and Ratiometric Fluorescence Cellular Imaging

In this study, we synthesized novel gold-carbon dots (GCDs) with unique properties by microwave-assisted method. The characterization of high-resolution transmission electron microscope (HRTEM), XRD, high-angle annular dark field scanning transmission electron microscope (HAADF-STEM), and energy dispersive spectrometer demonstrates that GCDs are composed of carbon and Au. Tiny Au clusters are dispersed in a 2 nm-size carbon skeleton, which integrates the properties of typical CDs and gold nanoclusters (AuNCs), displaying fascinating peroxidase-like activity and single excitation/dual emission. Dual emission of the GCDs exhibits different fluorescent response to the target species and enables the GCDs to be exploited for sensing and bioimaging. The highly photostable and biocompatible GCDs were applied to dual fluorescent imaging for breast cancer cells and normal rat osteoblast cells under a single excitation. Moreover, ratiometric fluorescence imaging was used to monitor Fe(3+) level in normal rat osteoblast cells.

Determination of blood potassium using a fouling-resistant PVDF–HFP-based optode

Monitoring potassium levels in blood is a significant aspect of clinical analysis. Here, we report a system for determination of potassium in blood which has the additional advantage of being blood-fouling resistant for safe and easy in situ sensing.