Simple one-step synthesis of highly luminescent carbon dots from orange juice: application as excellent bio-imaging agents

Highly photoluminescent carbon dots with a PL quantum yield of 9.3% have been prepared via a simple one-step synthesis route using waste paper as a novel carbon source. The as-prepared carbon dots have good water solubility, well distributed particle size and acceptable fluorescence lifetime. Besides, due to high photostability and biocompatibility, the obtained carbon dots are demonstrated as excellent probes in cellular imaging.

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

One-pot green synthesis of carbon dots by using Saccharum officinarum juice for fluorescent imaging of bacteria (Escherichia coli) and yeast (Saccharomyces cerevisiae) cells

Green synthesis of carbon dots from Ocimum sanctum for effective fluorescent sensing of Pb2+ ions and live cell imaging

Metal atom doping, an easy and convenient method, can optimize and tune the physical-chemical properties and photometrics of carbon dots (CDs). However, there are few reports on the preparation of metal-decorated CDs that give red emission and a high photoluminescence quantum yield (PLQY). Here, we demonstrate a zinc (existing in human body) ion-doping strategy to observably enhance the PLQY and lengthen the CD emission wavelength. The prepared Zn/ZnO-decorated CDs (Zn-CDs) produced red fluorescence (623nm) with a superior PLQY of 40.3%. Through a series of analyses, Zn-CDs were confirmed to contain an oxidation state and reduction state of Zn doping into the internal defects and surface of Zn-CDs. More valuably, the Zn-CDs had excellent chemical stability, photo-stability, long-term storage stability, and high biocompatibility, and therefore could be used as a robust red fluorescence probe for high-quality cellular imaging.

Carbon dots (CDs) have outstanding optical properties, biocompatibility, and photostability, making them attractive for imaging applications. A facile and green one-step hydrothermal synthesis method is proposed, which can be safely used in a wide range of applications such as chemical sensing, bioimaging, and optoelectronics. In this study, we report green synthesis of carbon dots from bitter orange juice (Citrus Aurantium) by hydrothermal treatment for the first time. We studied effects of time, temperature, and pH on fluorescence of CDs, characterized them using various spectroscopic and microscopic methods, and evaluated their toxicity to different cell lines. Identifying an optimum reaction condition of 180 ºC for 7 h heating gave CDs that showed pH-dependent fluorescence, with the largest fluorescence at a pH of 7.0. The CDs were 1-2 nm in size with a spherical morphology and negative surface charge. The CDs showed a high quantum yield of 19.9 %, reasonable photostability, excellent water solubility, and long fluorescence lifetime. A one step hydrothermal rout led to various hydrophilic functional groups on the surface of the CDs. Our results showed that the CDs were non-toxic over a large concentration range and effective for imaging of cells, indicating their potential as imaging probes in medical diagnostics and biosensor applications.

Carbon dots (CDs) have emerged as an exceptional alternative to traditional fluorescent probes for cellular imaging due to their high brightness, photostability, tunable fluorescence emission, and low toxicity. These properties make CDs ideal for applications requiring high sensitivity and minimal phototoxicity. However, their optimal potential is realized when combined with advanced fluorescence imaging techniques like fluorescence lifetime imaging microscopy (FLIM). FLIM provides deep insights into dynamic cellular behaviors by measuring fluorescence lifetimes, offering information that traditional intensity-based methods cannot measure. Thus, this review explores the optical properties and fluorescence mechanisms of CDs. The use of UV-vis absorption and photoluminescence (PL) spectroscopy is also discussed to illustrate the unique behavior of CDs. Their applications in cellular imaging, including organelle visualization and real-time tracking of intracellular processes, are examined. The combination of CDs with FLIM enhances the sensitivity of cellular imaging, enabling label-free, time-resolved measurements of cellular dynamics. This integration allows for precise monitoring of metabolic shifts, molecular interactions, and bacterial detection via multicolor imaging. Finally, we addressed the challenges and future directions in optimizing CDs and FLIM, with a focus on improving temporal and spatial resolution. The combination of CDs and FLIM holds transformative potential for advancing biomedical diagnostics and therapeutic monitoring.

Optical properties of pH-sensitive carbon-dots with different modifications

Cancer therapy and imaging remain multifaceted global health challenges for patients, investigators, and medical practitioners. RNA-based therapies, facilitated by nanotechnology, show great potential for targeted treatment due to their high specificity and adaptability. Chitosan nanoparticles (CS-NPs) are preferred over other polysaccharide-based nanocarriers due to their biocompatibility, biodegradability, stability, excellent gene loading capacity, and tunable physicochemical properties, which enable their modification for the co-delivery of therapeutic agents and imaging reagents. Chitosan polymer alterations occur specifically by covalent and non-covalent conjugations. Carbon dots (CDs) have been identified as nanofluorescent probes for cellular and molecular imaging due to their small size and excellent photoluminescent properties. This review proposes the recent advancements in combining RNA molecules and CDs in conjugates with chitosan nanocarriers. These nanoplatforms have shown great promise in addressing the most challenging issues encountered in cancer treatment, including targeted delivery, sustained release, protection against enzymatic degradation, and real-time tracking. Evaluating these integrated systems at an optimal level enhances the therapeutic effect and diagnostic accuracy, creating promising theranostic approaches for oncology. This paper summarizes recent research activities and upcoming trends to illustrate their potential to propel further advancements in cancer treatment nanomedicines. Graphical Abstract

Nitrogen and sulfur codoped carbon dots (CDs) were prepared from garlic by a hydrothermal method. The as-prepared CDs possess good water dispersibility, strong blue fluorescence emission with a fluorescent quantum yield of 17.5%, and excellent photo and pH stabilities. It is also demonstrated that the fluorescence of CDs are resistant to the interference of metal ions, biomolecules, and high ionic strength environments. Combining with low cytotoxicity properties, CDs could be used as an excellent fluorescent probe for cellular multicolor imaging. Moreover, the CDs were also demonstrated to exhibit favorable radical scavenging activity.

The development of functional copper nanoclusters (Cu NCs) is becoming increasingly widespread in consumer technologies due to their applications in cellular imaging and catalysis. Herein, we report a simple protein-directed synthesis of stable, water-soluble and fluorescent Cu NCs, using BSA as the stabilising agent. Meanwhile, in this study, hydrazine hydrate (N₂H₄·2H₂O) was used as the reducing agent. N₂H₄·2H₂O was a mild reducing agent suggesting that all processes could be operated at room temperature. The as-prepared Cu NCs showed red fluorescence with a peaking center at 620 nm (quantum yield 4.1%). The fluorescence of the as-prepared BSA-Cu NCs was responsive to pH in that the intensity of fluorescence increased rapidly by decreasing the pH from 12 to 6. Besides, with an arresting set of features including water-dispersibility, red fluorescence, good biocompatibility, surface-bioactivity and small size, the resultant BSA-Cu NCs could be used as probes for cellular imaging and catalysis. In this study, CAL-27 cells and the reaction of oxidation of styrene are used as models to achieve fluorescence imaging and elucidate the catalytic activity of the as-prepared BSA-Cu NCs.

Biocompatible bright orange emissive carbon dots: Multifunctional nanoprobes for highly specific sensing toxic Cr(VI) ions and mitochondrial targeting cancer cell imaging

Although various fluorescent‐based nanoparticles are treated as cellular imaging probes, approaching the construction of a biocompatible subcellular imaging probe is challenging. At the same time, the recognition of wasted pharmaceutical drugs by some fluorescent nanoprobes is important and urgently required. We report a “structural memory” concept for simple one‐pot synthesis of bright green fluorescent (quantum yield of up to 61%) carbon dots (C‐dots) from triphenylphosphonium (TPP) as a carbon precursor that will simultaneously act as an effective vehicle for mitochondria labeling in cancer cells and as a selective tetracycline sensor. The ubiquitous TPP residues upon the C‐dots’ surface easily recognize the cellular mitochondria. Tetracycline has been selectively and instantaneously detected through rapid fluorescence on‐off response from C‐dots where other drugs remained silent in nature, even after longer incubation. This quenching response is ascribed to the static quenching effect and position of functional groups of the targeted drug which can play a dominating role. The reason for strong fluorescence exhibition from C‐dots has been well explained by considering different factors. Such types of C‐dots have been shown to be universal mitochondria‐targeting nanoprobes, non‐cytotoxic, and effective as a tetracycline detector. This finding should open a new avenue for in‐vivo therapeutic application and sensing of pharmaceutical drugs in real clinical applications.

Fluorescent nitrogen and sulfur co-doped carbon dots from casein and their applications for sensitive detection of Hg2+ and biothiols and cellular imaging

Zn-doped carbon dots (Zn@C-210 calcination temperature at 210 °C and Zn@C-260 calcination temperature at 260 °C) were synthesized via an in situ calcination method using zinc citrate complexes as precursors, aiming to investigate the mechanisms of their distinctive fluorescence properties. A range of analytical methods were employed to characterize these nanomaterials. The mechanism study revealed that the coordination structure of Zn-O, formed through zinc doping, can induce a metal–ligand charge-transfer effect, which significantly increases the probability of radiative transitions between the excited and ground states, thereby enhancing the fluorescence intensity. The Zn@C-210 in a solid state and Zn@C-260 in water exhibited approximately 71.50% and 21.1% quantum yields, respectively. Both Zn@C-210 and Zn@C-260 exhibited excitation-independent luminescence, featuring a long fluorescence lifetime of 6.5 μs for Zn@C-210 and 6.2 μs for Zn@C-260. Impressively, zinc-doped CDs displayed exceptional biosafety, showing no acute toxicity even at 1000 mg/kg doses. Zn@C-210 has excellent fluorescence in a solid state, showing promise in anti-photobleaching applications; meanwhile, the dual functionality of Zn@C-260 makes it useful as a folate sensor and cellular imaging probe. These findings not only advance the fundamental understanding of metal-doped carbon dot photophysics but also provide practical guidelines for developing targeted biomedical nanomaterials through rational surface engineering and doping strategies.