A Mini Review on pH-Sensitive Photoluminescence in Carbon Nanodots

Sustainable lignocellulosic nanofibers-based films with sensitive humidity and pH response for UV-blocking food preservation

UV-induced photo-oxidation critically compromises food quality, necessitating advanced materials that simultaneously mitigate light degradation and enable real-time freshness monitoring. Here, the excellent UV-blocking films with sensitive humidity and pH response are developed by synergistically incorporating sodium ligninsulfonate-derived carbon quantum dots (L-CDs) via a simple microwave-assisted generation and light absorption of lignin from lignocellulosic nanofibers. The resulting films with hybrid structure can block 99.74 % (UV-C), 99.86 % (UV-B), and 87.90 % (UV-A) of radiation while maintaining 85.60 % visible light transmittance (600 nm), and has excellent mechanical strength (61.51 MPa). Under the protection of composite film, pork, strawberries and grapes all maintained longer freshness than unprotected controls. Profited from the protonation and deprotonation of L-CDs and the disconnection/reconstruction of hydrogen bonds, it shows sensitive humidity and pH response with changes in blue fluorescence. Furthermore, the conductivity of the composite film increases exponentially as the increase of humidity, showing excellent humidity response monitoring. As expected, the prepared composite film can detect changes in conductivity and resistance for monitoring the freshness of food. So, this work provides the development prospects for multi-functional composite films with UV-blocking and intelligent humidity & pH sensing for food preservation and intelligent monitoring.

Fluorescent Poly(ε-Caprolactone)s Micelles for Anticancer Drug Delivery and Bioimaging

Despite significant advancements in polymer-based nanomedicine, the clinical translation of biodegradable micellar drug delivery systems is limited due to premature drug release, low drug-loading capacity (DLC), and lack of inherent therapeutic and bioimaging functionalities. To overcome these challenges, we designed a novel poly(ε-caprolactone) (PCL)-based amphiphilic diblock copolymer that possesses inherent anticancer activity, fluorescence imaging capabilities, and multistimuli-responsive drug release. This platform features a fluorescent hydrophilic shell comprising of two triethylene glycol units and a hydrophobic core containing anticancer naphthalene moieties. This unique architecture imparts remarkable properties: the triethylene glycol units confer thermoresponsive behavior for precise drug release and enable intracellular tracking, while the naphthalene pendants enhance DLC (3.7%) through π-π interactions with doxorubicin (DOX). The micelles exhibit a low critical micelle concentration (7.8 × 10-3 g/L), demonstrate strong stability for long storage times, and show significant cytotoxicity against the MDA-MB-231 cell line, highlighting their combined therapeutic efficacy.

Natural biomass-derived carbon quantum dots: a path to antioxidant, anticancer, antibiofilm, and bacterial bioimaging potential

Eco-friendly, highly fluorescent, and biocompatible carbon quantum dots (CQDs) were synthesized from Typha angustifolia by the hydrothermal method. Fabricated CQDs were assessed for its bioimaging properties, anticancer potential, antibiofilm, and antioxidant activities. X-ray diffraction analysis indicates an amorphous nature, with an average particle size of 11 nm as observed in dynamic light scattering. TEM analysis revealed a uniform quasi-spherical-shaped structure. Photoluminescence studies reveal that CQDs exhibit an excitation at 390 nm with emissions at 484 nm and 474 nm. Water-soluble CQDs showed a potent antiproliferative effect against human breast cancer (MDA-MB-231) cell lines with an IC50 value of 70.55 ± 0.015 µg/mL. Fluorescent studies revealed that CQDs enhanced the intracellular reactive oxygen species level leading to the loss of mitochondrial membrane potential triggering the apoptotic pathway culminating to cell death in MDA-MB-231 cells. In addition, CQDs showed a potent free radical scavenging activity with an IC50 value of 21.1 ± 1.56 μg/mL exhibiting 94.69 ± 2.4% scavenging activity at the highest dose of 100 µg/mL. Furthermore, CQDs efficiently eradicated the biofilm-forming efficiency of Pseudomonas aeruginosa which frequently affects immunocompromised cancer patients. Cellular internalization studies in P. aeruginosa showed intense green fluorescence revealing the applicability of CQDs for bioimaging. Overall, the results indicate that CQDs fabricated from a natural source can serve as an excellent nanotheranostic and anti-infective agent for the treatment of triple-negative breast cancer.

Xylooligosaccharides, monosaccharides, and pH-sensitive carbon dots production from Toona sinensis branches using organic acid hydrolysis and hydrothermal treatment

The present study focused on exploring the effectiveness of delignification of the lignocellulosic biomass and pH-controlled organic acid hydrolysis in the cascade utilization of Toona sinensis branches (TB) for the production of xylooligosaccharides (XOS), monosaccharides and carbon dots (CDs). The hydrolysis of delignified TB with propionic acid (PA) resulted in a high XOS yield of 48.1 % at pH 3.0, 170 °C for 60 min. The PA hydrolyzates upon hydrolysis with xylanase yielded 61.2 % XOS. The solid residue from XOS production was subjected to cellulase hydrolysis, resulting in a glucose yield of 87.8 %. Furthermore, CDs were synthesized through a green hydrothermal method using the solid residue from cellulase hydrolysis as a precursor. These CDs exhibited excitation-independent and pH-dependent fluorescence properties. This study demonstrated the integrated utilization of TB for efficient production of XOS, monosaccharides, and pH-sensitive CDs.

Mechanism study of Dual-Emission ratiometric fluorescent pH-Sensitive carbon quantum dots and its application on mornitoring enzymatic catalysis

Carbon dots (CQD) have received significant attention as a novel ratiometric fluorescent pH nanoprobe, owing to their favorable optical properties and excellent biocompatibility. Despite their appealing features, the precise mechanism behind the pH-sensitive photoluminescence of CQDs remains to be fully understood. This study endeavors to unravel the mechanism underlying the pH-responsive ratiometric fluorescence in dual-emission CQDs, synthesized through a one-step hydrothermal method using o-phenylenediamine and oxalic acid as precursors. The resultant CQDs exhibit inherent dual-emission at wavelengths of 383 nm and 566 nm, with the ratiometric fluorescence response tailored by the ratio of precursors, providing a robust tool for pH sensing across a range of 2 to 6. Detailed characterizations, including chemical, morphological, and optical analyses, alongside theoretical insights from time-dependent density functional theory (TD-DFT), elucidate the mechanism underlying the pH-dependent luminescence, attributed to the electron cloud transmission between amide and adjacent carboxyl groups on the CQD surface. The superior performance of these CQDs in real-time pH monitoring is demonstrated through their application in glucose oxidase-catalyzed reactions, showcasing their potential as efficient, reliable nanoprobes for biomedical research and diagnostic applications.

Rational Synthesis of Highly Fluorescent N, S Co-Doped Carbon Dots Using Biogenic Creatinine for Cu2+ Analysis in Drinking Water

Herein, highly fluorescent sulfur and nitrogen co-doped carbon dots (N, S-CDs) had been employed as a fluorescent probe to analyze Cu2+ in drinking water. The biogenic creatinine is known to form a stable complex with Cu2+; hence, it was rationally selected as a bioinspired nitrogen substrate for the first time to enhance N, S-CDs selectivity towards Cu2+. Moreover, the literature was surveyed to guide the selection of sulfur and carbon sources to optimize N, S-CDs quantum yield (QY), so thiourea and disodium edetate are co-carbonized with biogenic creatinine at 270°C for 40 min and characterized using different techniques. The resulting N, S-CDs have a homogeneous particle size distribution and high QY (60.5% ± 2.09%, n = 5). The produced N, S-CDs fluorescence intensity (FI) had been quantitatively quenched by Cu2+, achieving a detection limit reached of 0.07 μM. The developed environmentally friendly and sustainable platform, according to the results of three widely greenness assessment tools and the innovative RGB 12 model, had been successfully employed to detect Cu2+ in drinking water with excellent recovery. Finally, as this sensing platform is rapid and selective, it can be successfully employed to determine the Cu2+ in real-life applications.

Carbon Dot-Laponite Hybrid Nanocomposites as Selective Turn-Off Sensors for Hg2+ Detection and Photoluminescence Quenching Mechanism

Motivated by the importance of Hg2+ detection in water due to its harmful effect on the environment and human health, we investigated a recently developed nanocomposite based on carbon dots (CDs) and LAPONITE as an optical chemical sensor using photoluminescence emission. While several studies have reported the Hg2+ detection using CDs' photoluminescence emission, there is a lack of in-depth investigation into the quenching mechanisms involved in turn-off sensors. In this study, we propose a Stern-Volmer analysis at three different temperatures (288, 298, and 303 K). The results indicated selectivity for Hg2+ over that of the other evaluated metal. The optimum detection range for Hg2+ was found to be 1-40 μM, with limits of detection and quantification of 2.5 and 8.3 μM, respectively. Using the Stern-Volmer models, we found that static quenching dominates over collisional quenching, possibly due to the complexation between nanocomposite's carboxylate groups and Hg2+. Additionally, the modified Stern-Volmer model, which accounts for the fractional accessibility of the fluorophores by the quenchers, suggests that some parts of the sensor are inaccessible to the quencher.

Mechanistic insights into pH-sensitive photoluminescence of carbon dots: The role of carboxyl group

We present a mechanistic study of pH-sensitive photoluminescence (PL) in two deliberately designed systems of carbon dots (CDs), which are relatively poor and rich in carboxyl groups anchored on their surfaces, denoted CDs-COOH(p) and CDs-COOH(r), respectively. The underlying PL mechanisms for the two contrasting CD systems are revealed to be different. As for CDs-COOH(p), the pH response of PL exhibits an asymmetric volcano-shaped pattern featuring dynamic and static quenching under acidic and alkaline conditions, dominated by the effects of hydrogen bonding and non-emissive ground-state complex, respectively. As for CDs-COOH(r), however, the pH response exhibits an interesting sigmoid-shaped pattern featuring PL quenching under acidic conditions but PL enhancement under alkaline conditions, both of which become more pronounced with increasing photoexcitation energy, exhibiting a nearly symmetric trumpet-shaped pattern. Such patterns of PL response to acidity/alkalinity and photoexcitation energy can be understood in terms of the prominent effect of excited-state proton transfer that is coupled to the surface emissive centers of the carboxyl group and can be effectively modulated via pH-regulated protonation/deprotonation. Our comparative analyses of the pH-regulated surface-sensitive PL quenching/enhancement behaviors in the two CD systems allow for elucidating the different surface-state-controlled PL mechanisms, highlighting the specific role of carboxyl groups in the pH-sensitive PL of CDs. The mechanistic insights gleaned from this work would be useful for CDs-based applications such as luminescence, sensing, and bioimaging.

Green synthesis of fluorescent N-doped carbon quantum dots from castor seeds and their applications in cell imaging and pH sensing

Water-soluble fluorescent N-doped carbon quantum dots (N-CQDs) were hydrothermally prepared through a green synthesis route using castor seeds as a single precursor and a hydrothermal method. Several experimental techniques have been used to characterize synthesized N-CQDs to confirm their structure and to verify their applicability in cell imaging and pH sensing. The synthesized N-CQDs were found to have are characterized by amorphous nature with a spherical shape with an average particle size of 6.57 nm as revealed from XRD and TEM measurements. The FTIR results reveal the presence of carboxylic and hydroxyl functional groups on the surface of the CQDs, which was also confirmed by XPS analysis. The fluorescence characterization of the synthesized N-CQDs showed blue emission and excitation dependence with good photostability. It was found that the optimal excitation and emission wavelengths were (λEx = 360) and (λEm = 432) nm, respectively. The fluorescence quantum yield (QY) of about 9.6% at the optimum excitation wavelength 360 nm. Moreover, the fluorescence intensity of N-CQDs showed good linear dependence with the pH values in ranges of 3.5 - 7.5 and 8 - 12 as well as high sensitivity for slight changes of pH values. According to these results, two fluorescent pH sensors were created based on acidic and basic media. The obtained N-CQDs have zeta potential of -21.86 mV and thus have excellent stability in water. Moreover, N-CQDs derived from the castor seeds have antimicrobial activity and exhibits low cytotoxicity to WI-13 cells with IC50 = 394.4 ± 13.8 µg/mL. The results of this study demonstrated that the synthesized N-CQDs derived from castor seeds can be used as pH sensing and antimicrobial materials. On the other hand, they are also promising in applications in cell imaging, thermo-sensing and optoelectronics.

Functional composite films incorporating triphala-derived carbon dots for extending chicken preservation

Triphala-based carbon dots (T-CDs) were successfully prepared using a simple one-step hydrothermal method. T-CDs were characterized by absorbance, fluorescence, Fourier-transform infrared, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. T-CDs showed bright blue fluorescence at 434 nm upon excitation at 360 nm. Functional composite films were prepared using poly(vinyl alcohol) and gelatin mixture by incorporating T-CDs and applied as a packaging film to extend the shelf life of chicken. The antibacterial activity of T-CDs against Listeria monocytogenes and Staphylococcus aureus was evaluated using well diffusion and colony count methods. T-CDs were evenly dispersed throughout the PVA/Gel solution to form a dense and uninterrupted film. They also formed strong bonds with polymer chains, which improved the tensile strength of the film from 32.44 to 42.70 MPa. Furthermore, the presence of T-CDs significantly enhanced the UV-blocking ability of the PVA/Gel films, achieving 99.7 % for UV-B and 97.2 % for UV-A. In addition, the PVA/Gel/T-CDs composite films showed excellent antioxidant, antimicrobial and UV-barrier properties, extending the shelf life of chicken. Therefore, the PVA/Gel/T-CDs composite films showed great potential as an active food packaging material to extend the shelf life and preserve the visual quality of packaged meat.

Preparation of Fe,Co,P-Codoping Peroxidase-like Green-Emitting Carbon Dots and Its Application in Monitoring the Freshness of Aquatic Products

Carbon dot (CD) nanozymes with excellent fluorescence properties and mimetic enzyme activity have exhibited great potential in monitoring the freshness of meat products. This paper reports the synthesis of Fe, Co, and P codoped CD nanozymes (quantum yields = 48.76%) through a one-step hydrothermal route. The product showed green fluorescence and peroxidase (POD) activity. Because the fluorescence intensity and emission wavelength of prepared CDs change with pH, a pH sensor has been developed to monitor the pH change caused by volatile biogenic amines during the spoilage process of aquatic products. Moreover, this CD biosensor has been used to realize the sensitive and visual detection of hypoxanthine (Hx, the marker of the spoilage of aquatic products) based on the inhibitory effect of Hx upon the POD activity of CDs. This study provides a new strategy for preparing high-quality CD nanozymes and its application in low-cost and visual monitoring of the freshness of aquatic products.

Alfalfa biomass as a green source for the synthesis of N,S-CDs via microwave treatment. Application as a nano sensor for nifuroxazide in formulations and gastric juice

BACKGROUND

Researchers have investigated different techniques for synthesis of carbon dots. These techniques include Arc discharge, laser ablation, oxidation, water/solvothermal, and chemical vapor deposition. However, these techniques suffer from some limitations like the utilization of gaseous charged particles, high current, high temperature, potent oxidizing agents, non-environmentally friendly carbon sources, and the generation of uneven particle size. Therefore, there was a significant demand for the adoption of a new technology that combines the environmentally friendly aspects of both bio-based carbon sourcing and synthesis technique.

RESULTS

Medicago sativa L (alfalfa)-derived N, S-CDs have been successfully synthesized via microwave irradiation. The N,S-CDs exhibit strong fluorescence (λex/em of 320/420 nm) with fluorescence quantum yield of 2.2 % and high-water solubility. The produced N,S-CDs were characterized using TEM, EDX, Zeta potential analysis, IR, UV-Visible, and fluorescence spectroscopy. The average diameter of the produced N, S-CDs was 4.01 ± 1.2 nm, and the Zeta potential was -24.5 ± 6.63 mv. The stability of the produced nano sensors was also confirmed over wide pH range, long time, and in presence of different ions. The synthesized N, S-CDs were employed to quantify the antibacterial drug, nifuroxazide (NFZ), by fluorescence quenching via inner filter effect mechanism. The method was linear with NFZ concentration ranging from 1.0 to 30.0 μM. LOD and LOQ were 0.16 and 0.49 μM, respectively. The method was applied to quantify NFZ in simulated gastric juice (SGJ) with % recovery 99.59 ± 1.4 in addition to pharmaceutical dosage forms with % recovery 98.75 ± 0.61 for Antinal Capsules® and 100.63 ± 1.54 for Antinal suspension®. The Method validation was performed in compliance with the criteria outlined by ICH.

SIGNIFICANCE AND NOVELTY

The suggested approach primarily centers on the first-time use of alfalfa, an ecologically sustainable source of dopped-CDs, and a cost-effective synthesis technique via microwave irradiation, which is characterized by low energy consumption, minimized reaction time, and the ability to control the size of the produced CDs. This is in line with the growing global recognition of the implementation of green analytical chemistry principles.

Stimuli-Responsive Chiral Cellulose Nanocrystals Based Self-Assemblies for Security Measures to Prevent Counterfeiting: A Review

The proliferation of misleading information and counterfeit products in conjunction with technical progress presents substantial worldwide issues. To address the issue of counterfeiting, many tactics, such as the use of luminous anticounterfeiting systems, have been investigated. Nevertheless, traditional fluorescent compounds have a restricted effectiveness. Cellulose nanocrystals (CNCs), known for their renewable nature and outstanding qualities, present an excellent opportunity to develop intelligent, optically active materials formed due to their self-assembly behavior and stimuli response. CNCs and their derivatives-based self-assemblies allow for the creation of adaptable luminous materials that may be used to prevent counterfeiting. These materials integrate the photophysical characteristics of optically active components due to their stimuli-responsive behavior, enabling their use in fibers, labels, films, hydrogels, and inks. Despite substantial attention, existing materials frequently fall short of practical criteria due to limited knowledge and poor performance comparisons. This review aims to provide information on the latest developments in anticounterfeit materials based on stimuli-responsive CNCs and derivatives. It also includes the scope of artificial intelligence (AI) in the near future. It will emphasize the potential uses of these materials and encourage future investigation in this rapidly growing area of study.

Polyhedral oligomeric silsesquioxane (POSS)-silicon/carbon quantum dots nanocomposites for cell imaging

Silicon quantum dots (SiQDs) and carbon quantum dots (CQDs) are renowned for their outstanding applications in fluorescence imaging and biosensing. However, their small size poses significant challenges in terms of preparation, collection, and purification. Polyhedral oligomeric silsesquioxanes (POSS), an organic-inorganic nanohybrid with a cage-like structure, has recently attracted considerable attention due to its excellent biocompatibility. In this research, we utilize the encapsulating properties of POSS to improve the optical property of SiQDs/CQDs through an in situ synthesis strategy, resulting in the production of blue-emitting POSS-SiQDs, green-emitting POSS-G-CNDs, and red-emitting POSS-R-CNDs. By examining their structural and optical characteristics, it is found that these hybrid materials exhibit excellent luminescent properties, biocompatibility and cell membrane permeability. This facilitates multicolor intracellular imaging and underscores their successful application in biological imaging. Our study presents a novel approach to synthesize POSS-QDs composite nanomaterials with new perspectives in biological imaging and medical diagnostics.

Organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH for biosensing, bioimaging and biotherapeutics applications

In recent years, organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH (DFR-MPs-pH) have been attracting much interest in fundamental application research fields. More and more scientific publications have reported the exploration of various DFR-MPs-pH systems that have unique dual-fluorescence ratiometry as the signal output, in-built and signal self-calibration functions to improve precise detection of targets. DFR-MPs-pH systems possess high-performance applications in biosensing, bioimaging and biomedicine fields. This review has comprehensively summarized recent advances of DFR-MPs-pH for the first time. First of all, the compositions and types of DFR-MPs-pH are introduced by summarizing different organic fluorophores-based molecule systems. Then, construction strategies are analyzed based on specific components, structures, properties and functions of DFR-MPs-pH. Afterward, biosensing and bioimaging applications are discussed in detail, primarily referring to pH sensing and imaging detection at the levels of living cells and small animals. Finally, biomedicine applications are fully summarized, majorly involving bio-toxicity evaluation, bio-distribution, biomedical diagnosis and therapeutics. Meanwhile, the current status, challenges and perspectives are rationally commented after detailed discussions of representative and state-of-the-art studies. Overall, this present review is comprehensive, in-time and in-depth, and can facilitate the following further exploration of new and versatile DFR-MPs-pH systems toward rational design, facile preparation, superior properties, adjustable functions and highly efficient applications in promising fields.

El Hamd M, Alshehri S, Helmy MI. Bioinspired Carbon Dots-Based Fluorescent Sensor for the Selective Determination of a Potent Anti-Inflammatory Drug in the Presence of Its Photodegradation Products

Herein, we synthesized biogenic carbon dots (CDs) with blue-shifted maximum excitation (λex/λem of 320/404 nm) from largely wasted tangerine seeds for the first time via a one-step hydrothermal method. The biogenic CDs exhibit a maximum excitation wavelength that overlaps with the absorption spectrum of ketorolac tromethamine (KETO) at 320 nm. The developed CDs serve as a turn-off fluorescent probe via an inner filter effect (IFE) quenching mechanism. The resulting CDs have high quantum yield (QY) (39% ± 2.89%, n = 5) and exhibited great performance toward KETO over a concentration range of 0.50-16.00 μg/mL with a limit of detection (LOD) = 0.17 μg/mL. The nanoprobe achieved a high % recovery in assaying KETO in tablet dosage form and had not been significantly affected by various interferents including co-formulated and co-administered drugs. The nanoprobe shows selectivity toward KETO, even in the presence of its photocatalytic degradation products. It can effectively investigate the elimination of KETO from aquatic systems and test its stability in pharmaceutical preparations. The developed nanoprobe underwent a comprehensive evaluation of its environmental impact using analytical eco-scale (AES), complex green analytical procedure index (Complex GAPI), and the Analytical GREEnness calculator (AGREE). The sustainability of the developed nano sensor was assessed and compared to the reported metal-based quantum dots probe for KETO using the innovative RGB 12 model, considering 12 white analytical chemistry (WAC) perspectives.

Carbon Dots for Multiuse Platform: Intracellular pH Sensing and Complementary Intensified T1-T2 Dual Imaging Contrast Nanoprobes

Measurement of pH in living cells is a great and decisive factor for providing an early and accurate diagnosis factor. Along with this, the multimodal transverse and longitudinal relaxivity enhancement potentiality over single modality within a single platform in the magnetic resonance imaging (MRI) field is a very challenging issue for diagnostic purposes in the biomedical field of application. Therefore, this work aims to design a versatile platform by fabricating a novel nanoprobe through holmium- and manganese-ion doping in carbon quantum dots (Ho-Mn-CQDs), which can show nearly neutral intracellular pH sensing and MRI imaging at the same time. These manufactured Ho-Mn-CQDs acted as excellent pH sensors in the near-neutral range (4.01-8.01) with the linearity between 6.01 and 8.01, which could be useful for the intracellular pH-sensing capability. An innumerable number of carboxyl and amino groups are present on the surface of the prepared nanoprobe, making it an excellent candidate for pH sensing through fluorescence intensity quenching phenomena. Cellular uptake and cell viability experiments were also executed to affirm the intracellular accepting ability of Ho-Mn-CQDs. Furthermore, with this pH-sensing quality, these Ho-Mn-CQDs are also capable of acting as T1-T2 dual modal imaging contrast agents in comparison with pristine Ho-doped and Mn-doped CQDs. The Ho-Mn-CQDs showed an increment of r1 and r2 relaxivity values simultaneously compared with only the negative contrast agent, holmium in holmium-doped CQDs, and the positive contrast agent, manganese in manganese-doped CQDs. The above-mentioned observations elucidate that its tiny size, excitation dependence of fluorescence behavior, low cytotoxicity, and dual modal contrast imaging capability make it an ideal candidate for pH monitoring in the near-neutral range and also as a dual modal MRI imaging contrast enhancement nanoprobe at the same time.

Multicolor emission-based nitrogen, sulfur and boron co-doped photoluminescent carbon dots for sequential sensing of Fe3+ and cysteine: RGB color sensor and live cell imaging

Herein, a simple hydrothermal synthesis is used to prepare multiple heteroatom-doped photoluminescent carbon dots (CDs) from thiourea (N and S source) and boric acid (B source) as precursors. The optical and physicochemical properties of the as-synthesized NSB-CDs were studied using UV-Vis, photoluminescence, TEM, FT-IR, XRD, Raman, and XPS analyses. The NSB-CDs exhibited excellent stability, high photostability, pH, and ionic strength tolerance; they retained their excellent stability independent of excitation. The NSB-CDs featured small sizes of approximately 3.2 ± 0.4 nm (range: 2.0-5.0 nm) as evidenced using TEM measurements. The NSB-CDs were used as a photoluminescent sensing platform to detect Fe3+ as well as cysteine (Cys) molecules. The competitive binding of Cys to Fe3+ resulted in NSB-CDs that retained their photoluminescence. For the rapid identification and quantification of Fe3+ and Cys, NSB-CDs were developed as a "switch-on" dual-function sensing platform. The linear detection range of Fe3+ was 0-20 μM (limit of detection [LOD]: 54.4 nM) and that of Cys was 0-50 μM (LOD: 4.9 nM). We also introduced a smartphone RGB analysis method for detecting low-concentration solutions based on digital images. The NSB-CDs showed no toxicity at 100 μg/mL. Photoluminescent probes for multicolor live-cell imaging can be used with NSB-CDs at this concentration, suggesting that NSB-CDs may be promising photoluminescent probes.

Lemon-derived carbon dots as antioxidant and light emitter in fluorescent films applied to nanothermometry

The design of luminescent nanomaterials for the development of nanothermometers with high sensitivity and free of potentially toxic metals has developed in several fields, such as optoelectronics, sensors, and bioimaging. In addition, luminescent nanothermometers have advantages related to non-invasive measurement, with their wide detection range and high spatial resolution at the nano/microscale. Our study is the first, to our knowledge, to demonstrate a detailed study of a fluorescent film (Film-L) thermal sensor based on carbon dots derived from lemon bagasse extract (CD-L). The CD-L properties were explored as an antioxidant agent; their cytotoxicity was evaluated by using a human non-tumoral skin fibroblast (HFF-1) cell line from an MTT assay. The CD-L were characterized by HRTEM, DLS, FTIR, UV-VIS, and fluorescence spectroscopy. These confirmed their particle size distribution below 10 nm, graphitic structure in the core and surface organic groups, and strong blue emission. The CD-L showed cytocompatibility behavior and scavenging potential reactive species of biological importance: O2•- and HOCl, with IC50 of 276.8 ± 4.0 and 21.6 ± 0.7, respectively. The Film-L emission intensities (I425 nm) are temperature-dependent in the 298 to 333 K range. The Film-L luminescent thermometer shows a maximum relative thermal sensitivity of 2.69 % K-1 at 333 K.

Bioimaging based on Poly(ethylenimine)-Coated Carbon Dots and Gold Nanoparticles for pH Sensing and Metal Enhanced Fluorescence

When exposed to specific light wavelengths, carbon dots (CDs), which tend to be fluorescent, can emit colorful light. It provides them with a lot of adaptability for different applications including bioimaging, optoelectronics, and even environmental sensing. Poly(ethylenimine) (PEI) coated carbon dots (PEI-CDs) with a long emission wavelength were synthesized via the hydrothermal method. The resultant CDs show strong fluorescence with quantum yield up to 20.2%. The PEI-CDs exist with distinct pH-sensitive features with pH values in the range of 2-14. The optical characteristics of CDs are pH-responsive due to the presence of different amine groups on PEI, which is a functional polycationic polymer. One of the most widely employed nanoparticles for improving the fluorescence plasmonic characteristics of a nanocomposite is gold. Gold nanoparticles were coupled with PEI-CDs in this assay by using the EDC-NHS coupling to increase the photoluminescence property of the PEI-CDs by using the metal-enhanced fluorescence approach. In the presence of gold nanoparticles, the fluorescence is enhanced 5-6 times. The likely mechanism in our investigation was primarily derived from enhancement of the intrinsic radiative decay rate rather than the local electric field impact. Moreover, PEI-CDs can be used as a bioimaging agent, as these molecules are nontoxic to the cells, and the positively charged PEI-CDs have the potential for nuclear targeting, allowing for electrostatic contact with DNA in the nucleus. This finding will expand the application that the PEI-CDs can be used in the future for targeted imaging applications.

Carbon Dots-Types, Obtaining and Application in Biotechnology and Food Technology

Materials with a "nano" structure are increasingly used in medicine and biotechnology as drug delivery systems, bioimaging agents or biosensors in the monitoring of toxic substances, heavy metals and environmental variations. Furthermore, in the food industry, they have found applications as detectors of food adulteration, microbial contamination and even in packaging for monitoring product freshness. Carbon dots (CDs) as materials with broad as well as unprecedented possibilities could revolutionize the economy, if only their synthesis was based on low-cost natural sources. So far, a number of studies point to the positive possibilities of obtaining CDs from natural sources. This review describes the types of carbon dots and the most important methods of obtaining them. It also focuses on presenting the potential application of carbon dots in biotechnology and food technology.

Fluorescence intensity and fluorescence lifetime measurements of various carbon dots as a function of pH

Measurement and monitoring of pH are essential in both the industry and academia. It is therefore important to continue developing novel, low-cost pH sensors that provide increased accuracy over long periods of time. Particularly promising are sensors based on materials that show pH-dependent fluorescence intensity (FI) and lifetime (FL). Carbon dots (CDs) are emerging as promising candidates because of their low cost, ease of manufacturing, low toxicity, and negligible photobleaching. However, little has been done to quantify the FI and FL values of CDs. Here we report the characterisation of the pH-dependent FI and FL of four novel solvothermal synthesised CDs. The fifth CD is used as a reference sample and was synthesised following a published synthesis. The precursors for the CDs include disperse blue 1 dye, phloroglucinol, m-phenylenediamine (m-PD), N, and N-dimethylformamide (DMF). The average diameter size of the CDs ranges from 1.5 to 15 nm. An excitation wavelength of 452 nm with a bandwidth of 45 nm was used to quantify the fluorescence in the pH range 5-9. Three CDs show a decreasing trend in FI with pH, while two CDs show an increasing trend. None of the CDs shows strong FL dependence. The FL changes around 0.5 ± 0.2 ns across the tested pH range. We suggest that the differences in the fluorescence trends can be attributed to the precursors chosen for synthesising the CDs.

Nanoparticles for Interrogation of Cell Signaling

Cell functions rely on signal transduction-the cascades of molecular interactions and biochemical reactions that relay extracellular signals to the cell interior. Dissecting principles governing the signal transduction process is critical for the fundamental understanding of cell physiology and the development of biomedical interventions. The complexity of cell signaling is, however, beyond what is accessible by conventional biochemistry assays. Thanks to their unique physical and chemical properties, nanoparticles (NPs) have been increasingly used for the quantitative measurement and manipulation of cell signaling. Even though research in this area is still in its infancy, it has the potential to yield new, paradigm-shifting knowledge of cell biology and lead to biomedical innovations. To highlight this importance, we summarize in this review studies that pioneered the development and application of NPs for cell signaling, from quantitative measurements of signaling molecules to spatiotemporal manipulation of cell signal transduction.

Photocatalytic Degradation of Methylene Blue Using N-Doped ZnO/Carbon Dot (N-ZnO/CD) Nanocomposites Derived from Organic Soybean

This study reports on successful synthesis of carbon dots (CDs), nitrogen-doped zinc oxide (N-ZnO), and N-ZnO/CD nanocomposites as photocatalysts for degradation of methylene blue. The first part was the synthesis of CDs utilizing a precursor from soybean and ethylenediamine as a dopant by a hydrothermal method. The second part was the synthesis of N-ZnO with urea as the nitrogen dopant carried out by a calcination method in a furnace at 500 °C for 2 h in an N2 atmosphere (5 °C min-1). The third part was the synthesis of N-ZnO/CD nanocomposites. The characteristics of CDs, N-ZnO, and N-ZnO/CD nanocomposites were analyzed through Fourier transform infrared (FTIR), UV-vis absorbance, photoluminescence (PL), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermal gravimetry analysis (TGA), field-emission scanning electron microscopy energy-dispersive spectroscopy (FESEM EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. Based on the HR-TEM analysis, the CDs had a spherical shape with an average particle size of 4.249 nm. Meanwhile, based on the XRD and HR-TEM characterization, the N-ZnO and N-ZnO/CD nanocomposites have wurtzite hexagonal structures. The materials of N-ZnO and N-ZnO/CD show increased adsorption in the visible light region and low energy gap E g. The E g values of N-ZnO and N-ZnO/CDs were found to be 2.95 and 2.81 eV, respectively, whereas the surface area (S BET) values 3.827 m2 g-1 (N-ZnO) and 3.757 m2 g-1(N-ZnO/CDs) belonged to the microporous structure. In the last part, the photocatalysts of CDs, N-ZnO, and N-ZnO/CD nanocomposites were used for degradation of MB (10 ppm) under UV-B light irradiation pH = 7.04 (neutral) for 60 min at room temperature. The N-ZnO/CD nanocomposites showed a photodegradation efficiency of 83.4% with a kinetic rate of 0.0299 min-1 higher than N-ZnO and CDs. The XRD analysis and FESEM EDS of the N-ZnO/CDs before and after three cycles confirm the stability of the photocatalyst with an MB degradation of 58.2%. These results have clearly shown that the N-ZnO/CD nanocomposites could be used as an ideal photocatalytic material for the decolorization of organic compounds in wastewater.

Green synthesis of multi-functional carbon dots from medicinal plant leaves for antimicrobial, antioxidant, and bioimaging applications

In this research work, carbon dots (CDs) were synthesized from the renewable leaves of an indigenous medicinal plant by the one-pot sand bath method, Azadirachta indica. The synthesized CDs were characterized for its optical properties using UV-Vis, Fluorescence and Fourier transform infrared (FT-IR) spectrophotometry and for structural properties using dynamic light scattering (DLS), X-ray Diffraction (XRD) and high resolution Transmission electron microscopy (HR-TEM). The synthesized CDs exhibited concentration dependent biocompatibility when tested in mouse fibroblast L929 cell line. The EC50 values of biomedical studies, free radical scavenging activity (13.87 μgmL-1), and total antioxidant capacity (38 μgmL-1) proved CDs were exceptionally good. These CDs showed an appreciable zone of inhibition when examined on four bacterial (two gram-positive and gram-negative) and two fungal strains at minimum concentrations. Cellular internalisation studies performed on human breast cancer cells (MCF 7- bioimaging) revealed the applicability of CDs in bioimaging, wherein the inherent fluorescence of CDs were utilised. Thus, the CDs developed are potential as bioimaging, antioxidants and antimicrobial agents.

Carbon nanosphere based bifunctional oxidoreductase nano-catalytic agent to mitigate hypoxia in cancer cells

Developing metal-free carbon nanozyme for tumor hypoxia is difficult. In biomedical applications, especially in the case of biomolecular detection, extensive research has been done on nanozymes with enzyme-mimicking catalytic activity. However, there are considerably fewer investigations on targeted nano-catalytic tumor therapy. Nano catalytic medicine-enabled chemotherapy is a safe and promising treatment strategy that involves the conversion of excess H₂O₂ into O₂ in a tumor environment. Here we have synthesized carbon nanosphere (CNS) using the Camellia sinensis plant (CS-CNS). Further surface functionalization was achieved via nitrilotriacetic acid conjugation (NTA@CS-CNS). A stability study of synthesized nanozyme in the presence of various cations, anions, and 5 different pH range suggested the robustness of carbon based nanoassembly. The catalytic in vitro study shows that NTA@CS-CNS mimics peroxidase and catalase using TMB and H₂O₂ as substrates. NTA@CS-CNS showed K_m and V_max values of ~ 193.2 μM and 0.43 μM/s, ~ 413 μM and 1.42 μM/s, and ~ 378 μM and 1.63 μM/s, respectively when H₂O₂ and TMB was used for CAT and POD activity. Results showed that NTA@CS-CNS in combination with SFN and laser irradiation reduces hypoxia. Hence, our study could pave the path for the development of different non-toxic nano catalytic therapy for tumors in cancerous cells.

Role of Noncovalent Interactions in N,P-Functionalized Luminescent Carbon Dots for Ultrasensitive Detection of Moisture in D2O: Boosting Visible-NIR Light Sensitivity

It is highly desirable to design cost-efficient and eco-friendly fluorometric sensors that can efficiently detect water contamination in D₂O and other expensive organic solvents. Herein, we have synthesized N,P-codoped carbon dots (N,P-CDs) from o-phenylene diamine (o-PDA) and H₃PO₄ through the bottom-up carbonization method. Heteroatom co-doping increases the absorption cross section in the visible-NIR range, followed by the formation of stable emissive states in longer-wavelength regions. We have critically investigated the noncovalent interactions (especially H-bonding interactions) of various surface functional groups with surrounding solvent media through a detailed structure-property correlation. Based on the sensitivity of noncovalent H-bonding interactions to the stability of longer-wavelength emissive domains, we have utilized these N,P-CDs as cost-effective fluorometric sensors of water/moisture contamination in D₂O especially under visible-NIR light; the optical sensitivity reaches up to 0.1 volume (%) level. The detailed sensing mechanism has been further supported by a computational study through a simple visualization approach by mapping and analyzing all possible noncovalent interactions between the CDs and the solvent medium.

Tuning the Luminescence of Microwave-Assisted N-Doped Fluorescent Carbon Dots: Bioimaging Applications and Label-Free Anti-Cancer Drug Delivery

Nanosized fluorescent carbon dots (Cdots) have gained a lot of attention in the recent years because of their superior properties, such as good biocompatibility, low toxicity, excellent chemical stability, resistance to photobleaching, and ease of chemical modification. Cdots are promising candidates for considerable applications in various fields: sensors, bioimaging, and drug delivery. Specifically, nitrogen-doped Cdots have attracted a huge interest because of their applicability in bioimaging and drug delivery. Conventional methods for the synthesis of Cdots have drawbacks, such as the use of organic solvents, the presence of side products, and the time required for synthesis. Keeping all these points in mind, herein, we report green methodology for the synthesis of water-soluble, blue-emitting, nitrogen-doped multifunctional Cdots under microwave irradiation within 3 min. The Cdots were prepared using citric acid and arginine as source materials and were characterized using various physicochemical techniques. A pH-responsive drug delivery system was then designed using anticancer drug doxorubicin and the synthesized Cdots. The biocompatibility of synthesized Cdots was analyzed against L929 normal cell line. The Cdots-DOX conjugates exhibited efficient anticancer activity against HeLa cells and also acted as excellent bioimaging agents.

Polyvinylpyrrolidone-passivated fluorescent iron oxide quantum dots for turn-off detection of tetracycline in biological fluids

Tetracycline is an antibiotic that has been prescribed for COVID-19 treatment, raising concerns about antibiotic resistance after long-term use. This study reported fluorescent polyvinylpyrrolidone-passivated iron oxide quantum dots (IO QDs) for detecting tetracycline in biological fluids for the first time. The as-prepared IO QDs have an average size of 2.84 nm and exist a good stability under different conditions. The IO QDs' tetracycline detection performance could be attributed to a combination of static quenching and inner filter effect. The IO QDs displayed high sensitivity and selectivity toward tetracycline and achieved a good linear relationship with the corresponding detection limit being 91.6 nM.

Fluorescent Carbon Dots from Food Industry By-Products for Cell Imaging

Herein, following a circular economy approach, we present the synthesis of luminescent carbon dots via the thermal treatment of chestnut and peanut shells, which are abundant carbon-rich food industry by-products. As-synthesized carbon dots have excellent water dispersibility thanks to their negative surface groups, good luminescence, and photo-stability. The excitation-emission behaviour as well as the surface functionalization of these carbon dots can be tuned by changing the carbon source (chestnuts or peanuts) and the dispersing medium (water or ammonium hydroxide solution). Preliminary in vitro biological data proved that the samples are not cytotoxic to fibroblasts and can act as luminescent probes for cellular imaging. In addition, these carbon dots have a pH-dependent luminescence and may, therefore, serve as cellular pH sensors. This work paves the way towards the development of more sustainable carbon dot production for biomedical applications.

Development of Red-Emissive Porphyrin Graphene Quantum Dots (PGQDs) for Biological Cell-Labeling Applications

Red and near-infrared emission is a highly desirable feature for fluorescent nanoparticles in biological applications mainly due to longer wavelengths more easily being able to deeply penetrate tissues, organs, skin, and other organic components, while less autofluorescence interference would be produced. Additionally, graphene quantum dots (GQDs) that contain unique optical and electrical features have been targeted for their use in cell labeling applications as well as environmental analysis. Their most desirable features come in the form of low toxicity and biocompatibility; however, GQDs are frequently reported to have blue or green emission light and not the more advantageous red/NIR emission light. Furthermore, porphyrins are a subgroup of heterocyclic macrocycle organic compounds that are also naturally occurring pigments in nature that already contain the desired red-emission fluorescence. Therefore, porphyrins have been used previously to synthesize nanomaterials and for nanoparticle doping in order to incorporate the red/NIR emission light property into particles that otherwise do not contain the desired emission light. Meso-tetra(4-carboxyphenyl)porphine (TCPP) is one type of porphyrin with a large conjugated π-electron system and four carboxyl groups on its exterior benzene rings. These two key characteristics of TCPP make it ideal for incorporation into GQDs, as it would design and synthesize red-emissive material as well as give rise to excellent water solubility. In this work, TCPP is used in tangent with cis-cyclobutane-1,2-dicarboxylic acid (CBDA-2), a biomass derived organic molecule, to synthesize "green" porphyrin-based graphene quantum dots (PGQDs) with red-emission. The obtained PGQDs were characterized by various analytical methods. Utilizing TEM, HRTEM, and DLS the size distribution of the particles was determined to be 7.9 ± 4.1, well within the quantum dot range of 2-10 nm. FT-IR, XPS, and XRD depicted carbon, nitrogen, and oxygen as the main elemental components with carbon being in the form of graphene and the main porphyrin ring of TCPP remaining present in the final PGQDs product. Lastly, absorption and fluorescence spectroscopy determined the excitation wavelength at 420 nm and the emission at 650 nm which was successfully utilized in the imaging of HeLa cells using confocal microscopy.

Broad-Spectrum Antibacterial Activity of Synthesized Carbon Nanodots from d-Glucose

Carbon nanodots, a class of carbon nano-allotropes, have been synthesized through different routes and methods from a wide range of precursors. The selected precursor, synthetic method, and conditions can strongly alter the physicochemical properties of the resulting material and their intended applications. Herein, carbon nanodots (CNDs) have been synthesized from d-glucose by combining pyrolysis and chemical oxidation methods. The effect of the pyrolysis temperature, equivalents of oxidizing agent, and refluxing time were studied on the product and quantum yield. In the optimum conditions (pyrolysis temperature of 300 °C, 4.41 equiv of H2O2, 90 min of reflux) CNDs were obtained with 40% and 3.6% of product and quantum yields, respectively. The obtained CNDs are negatively charged (ζ-potential = -32 mV), excellently dispersed in water, with average diameter of 2.2 nm. Furthermore, ammonium hydroxide (NH4OH) was introduced as dehydrating and/or passivation agent during CNDs synthesis resulting in significant improvement of both product and quantum yields of about 1.5 and 3.76-fold, respectively. The synthesized CNDs showed a broad spectrum of antibacterial activities toward different Gram-positive and Gram-negative bacteria strains. Both synthesized CNDs caused highly colony forming unit reduction (CFU), ranging from 98% to 99.99% for most of the tested bacterial strains. However, CNDs synthesized in the absence of NH4OH, due to a negatively charged surface enriched in oxygenated groups, performed better in zone inhibition and minimum inhibitory concentration. The elevated antibacterial activity of high-oxygen-containing carbon nanodots is directly correlated to their ROS formation ability.

Carbon Nanodots from an In Silico Perspective

Carbon nanodots (CNDs) are the latest and most shining rising stars among photoluminescent (PL) nanomaterials. These carbon-based surface-passivated nanostructures compete with other related PL materials, including traditional semiconductor quantum dots and organic dyes, with a long list of benefits and emerging applications. Advantages of CNDs include tunable inherent optical properties and high photostability, rich possibilities for surface functionalization and doping, dispersibility, low toxicity, and viable synthesis (top-down and bottom-up) from organic materials. CNDs can be applied to biomedicine including imaging and sensing, drug-delivery, photodynamic therapy, photocatalysis but also to energy harvesting in solar cells and as LEDs. More applications are reported continuously, making this already a research field of its own. Understanding of the properties of CNDs requires one to go to the levels of electrons, atoms, molecules, and nanostructures at different scales using modern molecular modeling and to correlate it tightly with experiments. This review highlights different in silico techniques and studies, from quantum chemistry to the mesoscale, with particular reference to carbon nanodots, carbonaceous nanoparticles whose structural and photophysical properties are not fully elucidated. The role of experimental investigation is also presented. Hereby, we hope to encourage the reader to investigate CNDs and to apply virtual chemistry to obtain further insights needed to customize these amazing systems for novel prospective applications.

Synthesis and Characterization of N-rich Fluorescent Bio-dots as a Reporter in the Design of Dual-labeled FRET Probe for TaqMan PCR: a Feasibility Study

DNA-based analytical techniques have provided an advantageous sensing assay in the realm of biotechnology. Bio-inspired fluorescent nanodots are a novel type of biological staining agent with excellent optical properties widely used for cellular imaging and diagnostics. In the present research, we successfully synthesized bio-dots with excellent optical properties and high-quantum yield from DNA sodium salt through the hydrothermal method. We conjugated the bio-dots with 3' Eclipse® Dark Quencher (Eclipse) labeled single strand oligodeoxyribonucleotide according to carbodiimide chemistry, to design a fluorescence resonance energy transfer (FRET) probe. The results confirmed the prosperous synthesis and surface functionalization of the bio-dot. Analysis of size, zeta potential, and FTIR spectroscopy verified successful bioconjugation of the bio-dots with probes. UV-Visibility analysis and fluorescence intensity profile of the bio-dot and bio-dot@probes represented a concentration-dependent quenching of fluorescent signal of bio-dot by Eclipse after probe conjugation. The results demonstrated that TaqMan PCR was not feasible using the designed bio-dot@probes. Our results indicated that bio-dot can be used as an efficient fluorescent tag in the design of fluorescently labeled oligonucleotides with high biocompatibility and optical features. This article is protected by copyright. All rights reserved.

Water stable, red emitting, carbon nanoparticles stimulate 3D cell invasion via clathrin-mediated endocytic uptake

Bright fluorescent nanoparticles with excitation and emission towards the red end of the spectrum are highly desirable in the field of bioimaging. We present here a new class of organic carbon-based nanoparticles (CNPs) with a robust quantum yield and fluorescence towards the red region of the spectrum. Using organic substrates such as para-phenylenediamine (PPDA) dispersed in diphenyl ether under reflux conditions, we achieved scalable amounts of CNPs with an average size of 27 nm. These CNPs were readily taken up by different mammalian cells, and we show that they prefer clathrin-mediated endocytosis for their cellular entry route. Not only can these CNPs be specifically taken up by cells, but they also stimulate cellular processes such as cell invasion from 3D spheroid models. This new class of CNPs, which have sizes similar to those of proteinaceous ligands, hold immense potential for their surface functionalization. These could be explored as promising bioimaging agents for biomedical imaging and intracellular drug delivery.

Towards N-N-Doped Carbon Dots: A Combined Computational and Experimental Investigation

The introduction of N doping atoms in the carbon network of Carbon Dots is known to increase their quantum yield and broaden the emission spectrum, depending on the kind of N bonding introduced. N doping is usually achieved by exploiting amine molecules in the synthesis. In this work, we studied the possibility of introducing a N-N bonding in the carbon network by means of hydrothermal synthesis of citric acid and hydrazine molecules, including hydrated hydrazine, di-methylhydrazine and phenylhydrazine. The experimental optical features show the typical fingerprints of Carbon Dots formation, such as nanometric size, excitation dependent emission, non-single exponential decay of photoluminescence and G and D vibrational bands in the Raman spectra. To explain the reported data, we performed a detailed computational investigation of the possible products of the synthesis, comparing the simulated absorbance spectra with the experimental optical excitation pattern. The computed Raman spectra corroborate the hypothesis of the formation of pyridinone derivatives, among which the formation of small polymeric chains allowed the broad excitation spectra to be experimentally observed.

Effect of Nitrogen-Doped Carbon Dots (NCDs) on the Characteristics of NCD/MIL-53(Fe) Composite and Its Photocatalytic Performance for Methylene Blue Degradation under Visible Light

Metal-organic framework composites, which are combined from metal-organic framework and advanced carbon material, have drawn great attention in many fields of application such as environmental remediation and catalysts. Within this paper, the carbon/MIL-53(Fe) composite was fabricated via an in situ synthesis, in which N-containing carbon dots (NCDs) were mixed with MOF precursors’ solutions under various ratios before going through the solvothermal stage. It was showed that the introduction of a certain amount of NCDs would affect characteristic features and improve the photocatalytic performance of final products. The optimal doping content of NCDs in NCD/MIL-53(Fe) composite was determined. SEM images showed that the M-140 appeared as hexagonal bipyramid-shaped crystals with an average size of 700 nm. Compared with pristine MIL-53(Fe), the M-140 was more visibly light-responsive, and its calculated band gap energy was approximately 2.3 eV. In addition, M-140 catalyst also displayed more excellent photocatalytic activity for Methylene Blue degradation in a pH range from 5 to 7. Under optimal conditions, MB was achieved within 60 minutes and the removal rate was nearly 100% after 5 cycles. The photocatalytic mechanism of the obtained NCD/MIL-53(Fe) composite was discussed.

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1-3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

Chitosan-derived hydrothermally carbonized materials and its applications: A review of recent literature

Chitosan (CS) is a linear polysaccharide biopolymer, one of the most abundant biowastes in the environment. This makes chitosan a potential material for a wide range of applications. To improve CS's properties, chitosan has to be chemically modified. Hydrothermal carbonization (HTC) is a sustainable process for converting chitosan to solid carbonized material. This article presents a review on the applications of hydrothermally treated chitosan in different fields such as water treatment, heavy metals adsorption, carbon dioxide capturing, solar cells, energy storage, biosensing, supercapacitors, and catalysis. Moreover, this review covers the impact of HTC process parameters on the properties of the produced carbon material. The diversity of applications indicates the great possibilities and multifunctionality of hydrothermally carbonized chitosan and its derivatives. The utilization of HTC-CS is expected to further expand as a result of the movement toward sustainable, environmentally-friendly resources. Thus, this review also recommends a few suggestions to improve the properties of HTC chitosan and its comprehensive applications.

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.