Fluorescent Carbon Dots an Effective Nano-Thermometer in Vitro Applications

Fluorescent Thermometers Based on Carbon Quantum Dots with Various Detection Modes for Intracellular Temperature Measurement

We report that carbon quantum dots (CQDs) synthesized via a hydrothermal process using anthraquinone derivatives and l-cysteine provide versatile detection modes, making them suitable for various experimental setups. By modification of the precursor structures, these CQDs can function as different types of fluorescent nanothermometers, including those based on fluorescence intensity, ratiometrics, and fluorescence lifetime. Notably, fluorescence lifetime-based CQDs demonstrate robust performance under a wide range of conditions, including variations in pH and ionic strength. The CQDs exhibit low cytotoxicity and high cellular uptake efficiency, enabling wash-free imaging and precise fluorescence lifetime-based temperature measurements at the single-cell level. Furthermore, we successfully measured temperature changes associated with biochemical reactions, including the increase in cellular temperature induced by mitochondrial depolarization. In addition, these fluorescence lifetime-based measurements could be cross-verified using their fluorescence intensity. These findings underscore the potential of CQDs as versatile and minimally invasive tools for nanoscale thermometry in live cells.

Intricacies of Carbon Dot Photoluminescence for Emerging Applications: A Review

Discovered only in 2004, carbon dots (CDs) have already traversed a long journey, generating many promising research directions. Its cheapness, ease of synthesis, high water-solubility, tunable emission, and excellent biocompatibility make it a single-point solution to many problems, and tremendous efforts were invested into understanding the structure-property-function relationship, which eases the engineering of the CD properties suitable for a desired application. From the usual random choice of precursors or carbon materials as a starting point in the early days, more systematic approaches are now available for choosing proper starting materials and appropriate experimental conditions (solvent medium, reaction temperature, reaction duration, pH, etc) to customize its photoluminescence. The presence of impurities has a crucial role in the outcome and applicability of photoluminescence. Recently, a significant focus has been on the long-wavelength emissive CDs, particularly in the red to near-infrared (NIR) regions, for better penetration into live cells and to circumvent autofluorescence problems. Proper design can harvest phosphorescence from CDs. Many excellent reviews are available, focusing on different facets of CD prospects. Hence, we will only highlight the importance of the optical properties of CDs and ways to modulate them. We will mention some of the new works that have appeared in the last five years.

Amino acid assisted synthesis of CDs: a novel paradigm in plant tissue culture media for enhanced cellular effects and biotechnological advancements

We report a green approach to prepare carbon dots (CDs) with fresh tomatoes as carbon sources and amino acids as dopants (ACDs) by a microwave assisted method. The synthesised CDs were analysed by UV-visible absorption spectroscopy, photoluminescence spectroscopy, high resolution transmission electron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy. An MTT assay was used to evaluate the cytotoxicity of CDs toward L929 cells and found that CDs exhibit low cytotoxicity. The effects of ACDs on seed germination were evaluated by treating pea seeds with various concentrations of CDs. The results demonstrated a significant increase in germination and seedling vigour compared to untreated controls. Subsequently, the application of ACDs was extended to plant tissue culture. Explants treated with ACDs exhibited enhanced growth and development, indicating improved morphogenesis and proliferation rates. This study highlights the potential of ACDs as an efficient, non-toxic growth promoter in both seed germination and plant tissue culture, paving the way for their application in sustainable agriculture and plant biotechnology.

Time-gated multi-dimensional luminescence thermometry via carbon dots for precise temperature mobile sensing

Luminescence thermometry presents precise remote temperature measurement capabilities but faces significant challenges in real-world applications, primarily stemming from the calibration's susceptibility to environmental factors. External factors can compromise accuracy, necessitating resilient measurement protocols to ensure dependable temperature (T) readings across various settings. We explore a novel three-dimensional (3D) approach based on time-gated (t) luminescence thermometric parameters, Δ(T,t), employing physical mixtures of surface-engineered carbon dots (CDs) based on dibenzoylmethane and rhodamine B. These CDs showcase enduring, temperature-responsive, and customizable phosphorescence, easily activated by low-power LEDs and distinguished by their prolonged emission time due to thermally activated delayed phosphorescence. Quantifying the thermal emission dependency is achievable through conventional spectrometer analyses or by capturing photographs with a smartphone's camera under flashlight illumination, yielding up to 30 time-gated ratiometric thermometric parameters per sample. Notably, within the temperature range of 23-45 °C, the maximum relative sensitivity of 7.9% °C-1 surpasses current state-of-the-art CD-based thermometers and ensures temperature readout with low-resolution portable devices as non-modified smartphones.

Lanthanide-based nanomaterials for temperature sensing in the near-infrared spectral region: illuminating progress and challenges

Being first proposed as a method to overcome limitations associated with conventional contact thermometers, luminescence thermometry has been extensively studied over the past two decades as a sensitive and fast approach to remote and minimally invasive thermal sensing. Herein, lanthanide (Ln)-doped nanoparticles (Ln-NPs) have been identified as particularly promising candidates, given their outstanding optical properties. Known primarily for their upconversion emission, Ln-NPs have also been recognized for their ability to be excited with and emit in the near-infrared (NIR) regions matching the NIR transparency windows. This sparked the emergence of the development of NIR-NIR Ln-NPs for a wide range of temperature-sensing applications. The shift to longer excitation and emission wavelengths resulted in increased efforts being put into developing nanothermometers for biomedical applications, however most research is still preclinical. This mini-review outlines and addresses the challenges that limit the reliability and implementation of luminescent nanothermometers to real-life applications. Through a critical look into the recent developments from the past 4 years, we highlight attempts to overcome some of the limitations associated with excitation wavelength, thermal sensitivity, calibration, as well as light-matter interactions. Strategies range from use of longer excitation wavelengths, brighter emitters through strategic core/multi-shell architectures, exploitation of host phonons, and a shift from double- to single-band ratiometric as well as lifetime-based approaches to innovative methods based on computation and machine learning. To conclude, we offer a perspective on remaining gaps and where efforts should be focused towards more robust nanothermometers allowing a shift to real-life, e.g., in vivo, applications.

Biomass-derived carbon dots as fluorescent quantum probes to visualize and modulate inflammation

Quantum dots, which won the Nobel Prize in Chemistry, have recently gained significant attention in precision medicine due to their unique properties, such as size-tunable emission, high photostability, efficient light absorption, and vibrant luminescence. Consequently, there is a growing demand to identify new types of quantum dots from various sources and explore their potential applications as stimuli-responsive biosensors, biomolecular imaging probes, and targeted drug delivery agents. Biomass-waste-derived carbon quantum dots (CQDs) are an attractive alternative to conventional QDs, which often require expensive and toxic precursors, as they offer several merits in eco-friendly synthesis, preparation from renewable sources, and cost-effective production. In this study, we evaluated three CQDs derived from biomass waste for their potential application as non-toxic bioimaging agents in various cell lines, including human dermal fibroblasts, HeLa, cardiomyocytes, induced pluripotent stem cells, and an in-vivo medaka fish (Oryzias latipes) model. Confocal microscopic studies revealed that CQDs could assist in visualizing inflammatory processes in the cells, as they were taken up more by cells treated with tumor necrosis factor-α than untreated cells. In addition, our quantitative real-time PCR gene expression analysis has revealed that citric acid-based CQDs can potentially reduce inflammatory markers such as Interleukin-6. Our studies suggest that CQDs have potential as theragnostic agents, which can simultaneously identify and modulate inflammatory markers and may lead to targeted therapy for immune system-associated diseases.

A review of the growing trend towards heteroatoms-doped carbon dots based on dopamine acting as a hybrid agent and detected analyte

Dopamine (DA) is a biomolecule that plays a critical part in the functioning of our brains by promoting motivation, maintaining focus, and altering mood. Excessive or low-level concentrations of DA in the human brain led to a dangerous neurological disorder. It is significantly important to trace the precise amount of DA to prevent such risky brain disease. Recently, heteroatoms-doped carbon dots (H-CDs) have attracted great attention for their capacity to detect biomolecules, metal ions, organic solvents, chemical dyes, etc. In this review, we have provided a comprehensive summary of the emerging trends in the heteroatom functional dopamine-doped carbon dots (DA-CDs), which are based on DA used as starting substances or functionalizing agents. Our analysis encompasses a detailed exploration of the synthetic methods, physical and chemical properties of carbon dots derived from dopamine, as well as their diverse range of applications. Additionally, we have also discussed the application of H-CDs in the dopmine detection by using various fluorescent, colorimetric, and electrochemical techniques.

Zero Thermal Quenching Phenomenon of Green Emitting Carbon Dots with High Biocompatibility and Stable Multicolor Biological Imaging in a Hot Environment

Carbon dots are emerging fluorescent nanomaterials with unique physical and chemical properties and a wide range of applications. Herein, we have designed and successfully synthesized thermally stable green emissive nitrogen-doped carbon dots (NCDs) with a photoluminescent quantum yield of 11.32% through facile solvent-free carbonization. NCDs demonstrated zero thermal quenching upon various temperatures modulating from 20 to 80 °C. The green emissive NCDs perform very stably even after heating them at 80 °C for 1 h. The thermal stability mechanism demonstrates that C═O and C═N functional groups control the particle aggregation and protect the fluorescent hub from photo-oxidation and thermal oxidation. Highly biocompatible CDs exhibit bright, stable, and multicolor emissions in T-ca cells under hot circumstances (25-45 °C). Additionally, NCDs offer long-term stability in the biosystem, as evidenced by the fact that the cell retains its brightness about 70% after prolonging the incubation time to 8 days. Furthermore, the fluorescent NCDs are utilized as in vivo imaging agents in the hot environment as they display bright and thermally stable imaging (27-45 °C) under 488 nm excitation. The results confirmed that the produced thermally stable NCDs could be used in biology and related medical fields that require hot environment imaging.

High biocompatible nitrogen and sulfur Co-doped carbon dots for Hg(II) detection and their long-term biological stability in living cells

Fluorescent carbon dots have been highly reported nanomaterials in recent times because of their excellent physio-chemical properties and various field of applications. Herein, a one-step hydrothermal approach was used to synthesize high biocompatible nitrogen and sulfur co-doped carbon dots, and examined their chemical sensing (Hg²⁺) and biological imaging properties. The N,S-CDs exhibited blue light, demonstrating a high quantum yield of up to 44.5% and excitation-independent fluorescent characteristics. Cytotoxicity was observed by CCK-8 assay using T-ca cells as a target source. Cell viability was recorded over 80% even after 7 days of treatment with a concentration up to 400 μg/mL, indicating low-toxicity of N,S-CDs. Notably, the bright blue fluorescence of N,S-CDs was quenched by introducing toxic Hg²⁺ ions into the solution. The detection limit was calculated to be about ∼3.5 nM, which is quite impressive compared to previous reports. Because of their low-toxicity, nano-size, and environment friendly properties, N,S-CDs could be excellent fluorescent agents for bio-imaging applications. The biological stability of fluorescent N,S-CDs was tested over time, and the findings were significant even after 8 days of incubation with T-ca cells. Because of good biocompatibility and bright fluorescence, N,S-CDs were suitable for in vivo imaging.

A novel antibacterial and fluorescent coating composed of polydopamine and carbon dots on the surface of orthodontic brackets

Many kinds of antibacterial coatings have been designed to prevent the adherence of bacteria onto the surface of a fixed orthodontic device of brackets. However, the problems such as weak binding force, undetectable, drug resistance, cytotoxicity and short duration needed to be solved. Thus, it has great value in developing novel coating methods with long-term antibacterial and fluorescence properties according to the clinical application of brackets. In this study, we synthesized blue fluorescent carbon dots (HCDs) using the traditional Chinese medicinal honokiol, which could cause irreversible killing effects on both gram-positive and gram-negative bacteria through positive charges on the surface and inducing reactive oxygen species (ROS) production. Based on this, the surface of brackets was serially modified with polydopamine and HCDs, taking advantage of the strong adhesive properties as well as the negative surface charge of polydopamine particles. It is found that this coating exhibits stable antibacterial properties in 14 days with good biocompatibility, which can provide a new solution and strategy to solve the series of hazards caused by bacterial adhesion on the surface of orthodontic brackets.

One-step microwave synthesis of red-emissive carbon dots for cell imaging in extreme acidity and light emitting diodes

Red emissive carbon dots (R-CDs) have received great attention in biological fields due to their deep tissue penetrability, great bioimaging capability, low interference from auto-fluorescence, and potential for optoelectronic applications. Herein, excitation-independent, highly acid-sensitive R-CDs were successfully obtained via one-step microwave treatment of o-phenylenediamine (o-PD) and phosphoric acid and carefully purified by column chromatography. The relationship between the fluorescence emission and surface groups of the R-CDs was studied in detail using XPS, NMR, and fluorescence spectroscopy, and the different mechanisms of action of the R-CDs and acid in H2O and ethanol were determined. The excellent anti-interference ability and biocompatibility of the R-CDs were confirmed, and the probes were successfully used for imaging A549 and Escherichia coli (E. coli) cells in extreme acidity. Finally, based on their relatively high quantum yield and long wavelength emission, the application potential of the R-CDs in the fabrication of red light-emitting diodes (LEDs) was investigated.

Highly Luminescent Nucleoside-Based N, P-Doped Carbon Dots for Sensitive Detection of Ions and Bioimaging

The efficient detection of Fe3+ and MnO4− in a water environment is very important and challenging due to their harmful effects on the health of humanity and environmental systems. Good biocompatibility, sensitivity, selectivity, and superior photophysical properties were important attributes of carbon dot-based CDs sensors for sensing applications. In this work, we synthesized N, P-co-doped carbon dots (N/P CDs) with guanosine 5′-monophosphate (GMP) as a green carbon source, with high fluorescence quantum yield in water (QY, 53.72%). First, the luminescent N/P CDs showed a three-state “on-off-on” fluorescence response upon the sequential addition of Fe3+ and F−, with a low detection limit of 12 nM for Fe3+ and 8.5 nM for F−, respectively. Second, the N/P CDs also exhibited desirable selectivity and sensitivity for toxic MnO4− detection with the limit of detection of 18.2 nM, through a turn-off mechanism. Moreover, the luminescent N/P CDs successfully monitored the aforementioned ions in environmental water samples and in Escherichia coli.