Synthesis of Fluorescent Nitrogen and Phosphorous Co-doped Carbon Quantum Dots for Sensing of Iron, Cell Imaging and Antioxidant Activities

Enhancing the production of PHA in Scenedesmus sp. by the addition of green synthesized nitrogen, phosphorus, and nitrogen-phosphorus-doped carbon dots

Plastic consumption has increased globally, and environmental issues associated with it have only gotten more severe; as a result, the search for environmentally friendly alternatives has intensified. Polyhydroxyalkanoates (PHA), as biopolymers produced by microalgae, might be an excellent option; however, large-scale production is a relevant barrier that hinders their application. Recently, innovative materials such as carbon dots (CDs) have been explored to enhance PHA production sustainably. This study added green synthesized multi-doped CDs to Scenedesmus sp. microalgae cultures to improve PHA production. Prickly pear was selected as the carbon precursor for the hydrothermally synthesized CDs doped with nitrogen, phosphorous, and nitrogen-phosphorous elements. CDs were characterized by different techniques, such as FTIR, SEM, ζ potential, UV-Vis, and XRD. They exhibited a semi-crystalline structure with high concentrations of carboxylic groups on their surface and other elements, such as copper and phosphorus. A medium without nitrogen and phosphorous was used as a control to compare CDs-enriched mediums. Cultures regarding biomass growth, carbohydrates, lipids, proteins, and PHA content were analyzed. The obtained results demonstrated that CDs-enriched cultures produced higher content of biomass and PHA; CDs-enriched cultures presented an increase of 26.9% in PHA concentration and an increase of 32% in terms of cell growth compared to the standard cultures.

Natural Biowaste Derived Fluorescent Carbon Quantum Dots: Synthesis, Characterization and Biocompatibility Study

In this present study, a straightforward and affordable method for the environmentally safe synthesis of carbon quantum dots (CQDs) by employing human hair as the carbon source without any need of chemicals was synthesized. CQDs obtained from human hair was further functionalized with Poly-L-Lysine to form PLLCQDs. The synthesized PLLCQDs was demonstrated numerous advantageous characteristics like strong fluorescence intensity, superior photostability, and outstanding water solubility. Various physicochemical characterization was employed to confirm successful formation of PLLCQDs including UV-vis Spectroscopy, Fluorescence Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). The size of synthesized PLLCQDs is 3 nm. The resultant PLLCQDs exhibited strong blue emission with a quantum yield of 28%. Under UV light, the synthesized PLLCQDs emit blue (at 365nm) fluorescence. The optimization of synthesis parameters including synthesis method, effect of reaction temperature, effect of reaction time and effect of reaction concentration have a significant impact on the quality and quantity of synthesized PLLCQDs, as well as their properties and applications. The effect of pH and UV radiation on synthesized PLLCQDs exhibited excellent photo and chemical stability. The cytotoxicity of bulk system (Hair precursor) and PLLCQDs was evaluated using fibroblast cell line (L929). The cell viabilities of 99.47% was obtained from L929 cells using MTT assay and it can applicably function as agents for cell labelling as a good bioimaging probe.

Multi-applications of carbon dots and polydopamine-coated carbon dots for Fe3+ detection, bioimaging, dopamine assay and photothermal therapy

Carbon dots (CDs) or CDs/polymer composites have been applied in numerous fields. Here, novel CDs were synthesized by carbonization of egg yolk, and characterized by TEM, FTIR, XPS and photoluminescence spectra. The CDs were found to be approximate sphere in shape with an average size of 4.46 ± 1.17 nm, and emitted bright blue photoluminescence under UV irradiation. The photoluminescence of CDs was found selectively quenched by Fe³⁺ in a linear manner in the range of 0.05-0.45 mM, meaning they could be applied for Fe³⁺ detection in solution. Moreover, the CDs could be uptaken by HepG2 cells to exhibit bright blue photoluminescence. The intensity could reflect the level of intracellular Fe³⁺, indicating they could be further used for cell imaging and intracellular Fe³⁺ monitoring. Next, dopamine was polymerized on the surface of CDs to obtain the polydopamine (PDA)-coated CDs (CDs@PDA). We found PDA coating could quench the photoluminescence of CDs via inner filter effect, and the degree of quenching was linearly related to the logarithm of DA concentration (Log C_DA). Also, the selectivity experiment indicated the method had a high selectivity for DA over a number of possible interfering species. This indicated the CDs in combination with Tris buffer could be potentially applied as the assay kit of dopamine. At last, the CDs@PDA exhibited excellent photothermal conversion capability, and they could efficiently kill HepG2 cells under NIR laser irradiation. Overall, the CDs and CDs@PDA in this work exhibited many excellent advantages, and could be potentially used for multi-applications, such as Fe³⁺ sensor in solution and cellular, cell imaging, dopamine assay kit, as well as photothermal agents for cancer therapy.

Novel Green Fluorescent Probe Stem From Carbon Quantum Dots for Specific Recognition of Tyrosinase in Serum and Living Cells

Tyrosinase (TYR), an important biomarker for melanoma, offered significant information early detection of melanoma and may decrease the likelihood of mortality. Therefore, this article constructed a highly sensitive and selective green fluorescent functionalized carbon quantum dots (TYR-CQDs) for tyrosinase (TYR) activity detection by one-step hydrothermal protocol utilizing catechol, citric acid and urea as precursors. The prepared TYR-CQDs illustrated excellent linear relationship and broad linear range with a low detection limit, which exhibited high accuracy and recovery in quantitative determination of TYR in human serum samples. Furthermore, the TYR-CQDs had successfully realized intracellular TYR detection owing to excellent biocompatibility, high anti-interference ability and good cellular imaging capability, suggesting the potential biomedical applications in early diagnosis of melanoma and other tyrosinase-related diseases.

Application of carbon dots in food preservation: a critical review for packaging enhancers and food preservatives

Carbon dots (CDs) have two unique advantages: one is ease of synthesis at low price, the other is desirable physical and chemical properties, such as ultra-small size, abundant surface functional groups, nontoxic/low-toxicity, good biocompatibility, excellent antibacterial and antioxidant activities etc. These advantages provide opportunities for the development of new food packaging enhancers and food preservatives. This paper systematically reviews the studies of CDs used to strengthen the physical properties of food packaging, including strengthen mechanical strength, ultraviolet (UV) barrier properties and water barrier properties. It also reviews the researches of CDs used to fabricate active packaging with antioxidant and/or antibacterial properties and intelligent packaging with the capacity of sensing the freshness of food. In addition, it analyzes the antioxidant and antibacterial properties of CDs as preservatives, and discusses the effect of CDs applied as coating agents and nano-level food additives for extension the shelf life of food samples. It also provides a brief review on the security and the release behavior of CDs.

Biomass-derived carbon quantum dots: a novel and sustainable fluorescent "ON-OFF-ON" sensor for ferric ions

Fluorescent carbon dot sensing probes have attracted much attention in recent times due to their amazing properties regarding chemical inertness, solubility, non-toxicity, optoelectronic behavior, and charge transport functionality. Herein, we report the green synthesis of lotus stem-derived carbon dots (LS-CQDs) from the naturally available lotus stem by a simple and economical hydrothermal method without the use of an oxidizing agent. HR-TEM and DLS measurements confirm the quasi-spherical shaped LS-CQDs, with a 2.5 nm average diameter. The LS-CQDs possess better aqueous dispersibility and stability due to the presence of hydrophilic hydroxyl, carboxyl, and amine surface functional groups, as manifested by FT-IR analysis. The LS-CQDs demonstrate excellent fluorescence properties that are sensitive to conditions of pH, time, and temperature. Furthermore, the prepared LS-CQDs display an interesting fluorescence "ON-OFF-ON" property. The LS-CQDs depict a selective and sensitive fluorescence quenching response in the presence of ferric ions. Moreover, the prepared LS-CQDs exhibit a quantum yield of about 0.44%. The LS-CQDs show an excellent sensing response with the limit of detection (LOD) equal to 0.212 ppm. The promising sensitivity and selectivity of LS-CQDs were utilized for the detection of ferric ions in the water samples collected from three polluted sources viz. lake water (Dal lake), underground water (tube well), and stream water. For all the collected water samples the results were reasonably good with the achievement of recovery factor above 1. Therefore, we strongly believe that the present study will serve as a good guiding star for the selective and sensitive detection of ferric ions from various polluted water bodies.

Recent Advances in Carbon Nanodots: A Promising Nanomaterial for Biomedical Applications

Carbon nanodots (CNDs) are an emerging class of nanomaterials and have generated much interest in the field of biomedicine by way of unique properties, such as superior biocompatibility, stability, excellent photoluminescence, simple green synthesis, and easy surface modification. CNDs have been featured in a host of applications, including bioimaging, biosensing, and therapy. In this review, we summarize the latest research progress of CNDs and discuss key advances in our comprehension of CNDs and their potential as biomedical tools. We highlighted the recent developments in the understanding of the functional tailoring of CNDs by modifying dopants and surface molecules, which have yielded a deeper understanding of their antioxidant behavior and mechanisms of action. The increasing amount of in vitro research regarding CNDs has also spawned interest in in vivo practices. Chief among them, we discuss the emergence of research analyzing CNDs as useful therapeutic agents in various disease states. Each subject is debated with reflection on future studies that may further our grasp of CNDs.