Carbon Quantum Dots Prepared with Chitosan for Synthesis of CQDs/AuNPs for Iodine Ions Detection

Chitosan/MgO NPs/CQDs bionanocomposite coating: Fabrication, characterization and determination of antimicrobial efficacy

The development of new polymer nanocomposites or antibacterial coatings is crucial in combating drug-resistant infections, particularly bacterial infections. In this study, a new chitosan polymer based nanocomposite reinforced with magnesium oxide nanopowders and carbon quantum dots was fabricated by sol-gel technique and coated on 316 L stainless steel. In order to gaining the optimal amount of components to achieve the maximum antibacterial properties, the effect of concentration of nanocomposite components on its antibacterial properties was investigated. Crystal structure, microstructure, elemental dispersion, size distribution, chemical composition and morphology of nanocomposite and coating were characterized with various analyses. The obtained results exhibited that the carbon quantum dot and magnesium oxide nanopowders were distributed uniformly and without agglomeration in the chitosan matrix and created a uniform coating. The antibacterial properties of the synthesized samples against Staphylococcus aureus bacteria (gram positive) were evaluated using disk diffusion and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) antibacterial tests. The inhibition growth zone formed around the antibiotic and nanocomposite 25 mg/ml under dark and light was about 32 and 14, 11 mm, respectively. Also, MIC and MBC values for final nanocomposite were 62.5 and 125 μg/ml, respectively.

A highly sensitive fluorescence nanosensor for determination of amikacin antibiotics using composites of carbon quantum dots and gold nanoparticles

Amikacin is an aminoglycoside antibiotic widely used to treat various bacterial infections in humans. However, elevated concentrations of amikacin can damage the cochlear nerve. Thus, accurate and rapid amikacin detection is crucial. In this study, we developed an "on-off" fluorescence nanosensor for highly sensitive amikacin determination based on a composite of carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). The method quenches CQD fluorescence (turn-off) when they bind to AuNPs but restores it (turn-on) when amikacin binds and releases the CQDs. Adding Cu2+ enhances sensitivity by cross-linking amikacin-coated AuNPs. Under optimal conditions (pH 4, 1 mM Na2SO4, 1 mM CuSO4), the method achieved a low detection limit of 3.5 × 10-11 M (0.02 ppb), a wide linear range (10-10 to 10-8 M), high precision (RSD < 5 %), and a rapid 2-minute response time. Exceptional selectivity was observed over other antibiotics. The CQDs/AuNPs-based sensor successfully detected amikacin in pharmaceutical and surface water samples. This approach offers a fast on-site analytical method for amikacin detection, with potential applications in clinical and environmental settings.

Carbon Dots: From Synthesis to Unraveling the Fluorescence Mechanism

Carbon dots (CDs) being a new type of carbon-based nanomaterial have attracted intensive interest from researchers owing to their excellent biophysical properties. CDs are a class of fluorescent carbon nanomaterials that have emerged as a promising alternative to traditional quantum dots and organic dyes in applications including bioimaging, sensing, and optoelectronics. CDs possess unique optical properties, such as tunable emission, facile synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and environmental areas. The synthesis of CDs is achievable by a variety of methods, including bottom-up and top-down approaches, involving the use of different carbon sources and surface functionalization strategies. However, understanding the fluorescence mechanism of CDs remains a challenge. Various mechanistic models have been proposed to explain their origin of luminescence. This review summarizes the recent developments in the synthesis and functionalization of CDs and provides an overview of the current understanding of the fluorescence mechanism.

Multifunctional Lipophobic Polymer Dots from Cyclodextrin: Antimicrobial/Anticancer Laborers and Silver Ions Chemo-Sensor

β-Cyclodextrin (CD) is currently exploited for the implantation of lipophobic polymer dots (PDs) for antimicrobial and anticancer laborers. Moreover, the PDs were investigated to act as a chemo-sensor for metal detection. The data revealed that under basic conditions, photoluminescent PDs (5.1 nm) were successively clustered with a controllable size at 190 °C, whereas under acidic conditions, smaller-sized non-photoluminescent carbon nanoparticles (2.9 nm) were obtained. The fluorescence intensity of synthesized PDs under basic conditions was affected by pH, and such an intensity was significantly higher compared to that prepared under acidic conditions. The PDs were exploited as florescent detectors in estimation of Ag⁺ ions in aquatic streams. Treatment of Ag⁺ ion colloids with PDs resulted in fluorescence quenching attributing to the production of AgNPs that approved by spectral studies. The cell viability percent was estimated for Escherichia coli, Staphylococcus aureus, and Candida albicans after incubation with PDs implanted under basic conditions for 24 h. The cell mortality percent was estimated for breast cancer (MCF-7) after incubation with different concentrations of PDs that were implanted under acidic versus basic conditions to show that treatment of the tested cells with 1000 μg/mL PDs prepared under basic (IC50 232.5 μg/mL) and acidic (IC₅₀ 88.6 μg/mL) conditions resulted in cell mortality percentages of 70 and 90%, respectively.

Ultrasensitive iodide detection in biofluids based on hot electron-induced reduction of p-Nitrothiophenol on Au@Ag core-shell nanoparticles

Surveillance of iodine intake is important because either inadequate or excessive amount of iodine may lead to thyroid malfunctions. Herein, we report a method for fast iodide quantification based on a plasmonic hot electron-driven chemical reaction, which occurs on Au@Ag core-shell nanoparticles (NPs) coated with p-nitrothiophenol (PNTP) molecules. Upon resonant light illumination, hot electron-hole pairs are generated in the NPs. The hot holes capture iodide ions (I^-) and form AgI which decomposes under light; while the hot electrons are shifted to the electron orbital (LUMO) of PNTP and trigger its reduction to p-aminothiophenol (PATP). By measuring characteristic surface-enhanced Raman spectroscopic (SERS) peaks of PNTP and PATP, the concentration of I^- in water can be quantitatively determined, with a linear response in the 0.5-20 μM range and a detection limit of 0.30 μM. The Au@Ag nanosensor was then applied for I^- detection in various biofluids including urine, serum and saliva, exhibiting superior detection sensitivity and high selectivity. This sensing assay requires a small sample volume of ∼10 μL and completes the entire detection process in ∼2 min, and therefore holds significant potential for application in point-of-care settings.

Colorimetric and visual determination of iodide ions via morphology transition of gold nanobipyramids

The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I^- in kelp was detected by etching Au NBPs in the presence of IO₃^-. Under acidic conditions, IO₃^- reacted rapidly with I^- to form I₂, subsequently I₂ reacted with I^- to form the intermediate I₃^-. In the presence of CTAB, Au NBPs were etched by I₂ derived from I₃^-, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I^- with the naked eye. A linear relationship can be found between the LSPR peak changes with the I^- concentration in a wide range from 4.0 μM to 15.0 μM, and the sensitive limit of detection (LOD) was 0.2 μM for UV-vis spectroscopy and the obvious color changes with a visual LOD was 4.0 μM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I^- in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I^- in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.

Polysaccharide-based C-dots and polysaccharide/C-dot nanocomposites: fabrication strategies and applications

C-dots are a new class of materials with vast applications. The synthesis of bio-based C-dots has attracted increasing attention in recent years. Polysaccharides being the most abundant natural materials with high biodegradability and no toxicity have been the focus of researchers for the synthesis of C-dots. C-dots obtained from polysaccharides are generally fabricated via thermal procedures, carbonization, and microwave pyrolysis. Small size, photo-induced electron transfer (PET), and highly adjustable luminosity behavior are the most important physical and chemical properties of C-dots. However, C-dot/polysaccharide composites can be introduced as a new generation of composites that combine the features of both C-dots and polysaccharides having a wide range of applications in biomedicines, biosensors, drug delivery systems, etc. This review demonstrates the features, raw materials, and methods used for the fabrication of C-dots derived from different polysaccharides. Furthermore, the properties, applications, and synthesis conditions of various C-dot/polysaccharide composites are discussed in detail.

Synthesis of luminescent chitosan-based carbon dots for Candida albicans bioimaging

In this work, we used chitosan as a raw material to synthesize carbon dots using fast microwave carbonization. We studied the influence of the synthesis time, doping agent, and the molar ratio between the reactants on the quantum yield of carbon dots. Chitosan-based carbon dots displayed stable blue fluorescence emission with excitation-dependent behavior and quantum yield values ranging from 1.16 to 7.07 %. ANOVA results showed that the interaction factor between the doping agent and the molar ratio of the reactants was a significant combination to produce carbon dots with higher quantum yield. The presence of the doping agent improved the carbon dots optical properties by obtaining higher fluorescence intensity values. Confocal laser microscope images showed that the carbon dots internalized in the Candida albicans cellular membrane, exhibiting blue, green, and red emissions, acting as a promising agent for bioimaging.

Ti3C2 MXene-derived Li4Ti5O12 nanoplates with in-situ formed carbon quantum dots for metal-ion battery anodes

Two-dimensional (2D) material Ti3C2 MXenes have recently been used in electrode composites for lithium-ion batteries (LIBs) for their excellent electrical conductivity and accordion-like nanosheet morphology. However, Ti3C2 has low specific capacity and fast degradation rate upon cycling after inevitably coupling with surface species during synthesis. In this work, Ti3C2 is used as Ti-source for Li4Ti5O12 (LTO) and C-source for carbon quantum dots (CQDs) in a one-step hydrothermal process. The resultant LTO product (M-LTO) inherits the nanosheet morphology of Ti3C2 with uniformly anchored CQDs. The highly electronic conductive CQDs optimize the transmission path of ions which reduces the diffusion barrier of ions, and they further increase the density of states of the material which effectively improving the conductivity of M-LTO. Remarkable electrochemical performances including high initial specific capacity, long lifetime and excellent low temperature capacity are demonstrated for this type of electrode in LIBs, sodium ion batteries (SIBs) and lithium-magnesium ion hybrid batteries (LMIHBs). This paper offers a new strategy to the rapidly expanding research on the application of transition metal MXenes in electrodes for metal-ion batteries.

Copper-Doped Carbon Nanodots with Superior Photocatalysis, Directly Obtained from Chromium-Copper-Arsenic-Treated Wood Waste

An ecofriendly approach was developed for preparing copper-doped carbon dots (CDs) with superior photocatalysis using chromium-copper-arsenic (CCA)-treated wood waste as a precursor. Original wood (W-CDs), CCA-treated wood (C-CDs), and bioremediation CCA wood (Y-CDs) were used as the precursors. The chemical composition and structural, morphological, and optical properties, as well as the photocatalytic ability of the synthesized CDs varied with wood type. The C-CDs and W-CDs had similar characteristics: quasispherical in shape and with a diameter of 2 to 4.5 nm. However, the Y-CDs particles were irregular and stacked together, with a size of 1.5-3 nm. The presence of nitrogen prevented the formation of an aromatic structure for those CDs fabricated from bioremediation CCA wood. The three synthesized CDs showed a broad absorption peak at 260 nm and a weak absorption peak at 320 nm. Proof of the model study for the fabrication of luminescent CDs from CCA wood waste for bioimaging was provided. The degradation rate of CD photocatalytic MB was 97.8% for 30 min. Copper doping gives the CDs electron acceptor properties, improving their photocatalytic efficiency. This study provides novel ways to prepare nanomaterials from decommissioned wood as a nontoxic and low-cost alternative to fluorescent dots.

Chitosan-Based Carbon Dots with Applied Aspects: New Frontiers of International Interest in a Material of Marine Origin

Carbon dots (CDs) have attracted significant research attention worldwide due to their unique properties and advantageous attributes, such as superior optical properties, biocompatibility, easy surface functionalization, and more. Moreover, biomass-derived CDs have attracted much attention because of their additional advantages related to more environmentally friendly and lower-cost synthesis. In this respect, chitosan has been recently explored for the preparation of CDs, which in comparison to other natural precursors exhibited additional advantages. Beyond the benefits related to the eco-friendly and abundant nature of chitosan, using it as a nanomaterial precursor offers additional benefits in terms of structure, morphology, and dopant elements. Furthermore, the high content of nitrogen in chitosan allows it to be used as a single carbon and nitrogen precursor for the preparation of N-doped CDs, significantly improving their fluorescent properties and, therefore, their performances. This review addresses the most recent advances in chitosan-based CDs with a special focus on synthesis methods, enhanced properties, and their applications in different fields, including biomedicine, the environment, and food packaging. Finally, this work also addresses the key challenges to be overcome to propose future perspectives and research to unlock their great potential for practical applications.

Preparation and Characterization of Salsalate-Loaded Chitosan Nanoparticles: In Vitro Release and Antibacterial and Antibiofilm Activity

The controlled-release characteristic of drug delivery systems is utilized to increase the residence time of therapeutic agents in the human body. This study aimed to formulate and characterize salsalate (SSL)-loaded chitosan nanoparticles (CSNPs) prepared using the ionic gelation method and to assess their in vitro release and antibacterial and antibiofilm activities. The optimized CSNPs and CSNP-SSL formulation were characterized for particle size (156.4 ± 12.7 nm and 132.8 ± 17.4 nm), polydispersity index (0.489 ± 0.011 and 0.236 ± 132 0.021), zeta potential (68 ± 16 mV and 37 ± 11 mV), and entrapment efficiency (68.9 ± 2.14%). Physicochemical features of these nanoparticles were characterized using UV-visible and Fourier transform infrared spectroscopy and X-ray diffraction pattern. Scanning electron microscopy studies indicated that CSNPs and CSNP-SSL were spherical in shape with a smooth surface and their particle size ranged between 200 and 500 nm. In vitro release profiles of the optimized formulations showed an initial burst followed by slow and sustained drug release after 18 h (64.2 ± 3.2%) and 48 h (84.6 ± 4.23%), respectively. Additionally, the CSNPs and CSNP-SSL nanoparticles showed a sustained antibacterial action against Staphylococcus aureus (15.7 ± 0.1 and 19.1 ± 1.2 mm) and Escherichia coli (17.5 ± 0.8 and 21.6 ± 1.7 243 mm). Interestingly, CSNP-SSL showed better capability (89.4 ± 1.2% and 95.8 ± 0.7%) than did CSNPs in inhibiting antibiofilm production by Enterobacter tabaci (E2) and Klebsiella quasipneumoniae (SC3). Therefore, CSNPs are a promising dosage form for sustained drug delivery and enhanced antibacterial and antibiofilm activity of SSL; these results could be translated into increased patient compliance.

A Highly Selective and Sensitive Nano-Silver sol Sensor for Hg2+ and Fe3+: Green Preparation and Mechanism

The development of highly selective and highly sensitive nanometer colorimetric chemical sensors is an urgent requirement in the immediate detection of heavy metal ions. In this work, silver-nanoparticle (Ag NPs)-based chemosensors were prepared by a simple and green method, in which the silver nitrate, carboxymethyl cellulose sodium (CMS) and Polyvinylpyrrolidone (PVP), and glucose are used as the silver source, double stabilizer and green reductant, respectively. The obtained colloidal CMS/PVP-Ag NPs showed a high dispersibility and stability, and creating a high selectivity and sensitivity to detect Hg2+ and Fe3+ with remarkable and rapid color variation. Low limits of detection (LOD) of 7.1 nM (0–20 μM) and 15.2 nM (20–100 μM) for Hg2+ and 3.6 nM for Fe3+ were achieved. More importantly, the CMS/PVP-Ag NPs has a high sensitivity even in a complex system with multiple heavy ions, the result of the practical ability to detect Hg2+ and Fe3+ in tap water and seawater reached a rational range of 98.33~104.2% (Hg2+) and 98.85~104.80% (Fe3+), indicating the great potential of the as-prepared nanocomposites colorimetric chemosensor for practical applications.

Gold Nanomaterials and their Composites as Electrochemical Sensing Platforms for Nitrite Detection

Nitrite is one of the abundant toxic components existing in the environment and is likely to have a great potential to affect human health badly. For that reason, it has become crucial to build a reliable nitrite detection method. In recent years, several nitrite monitoring systems have been proposed. Compared with traditional analytical strategies, the electrochemical approach has a bunch of advantages, including low cost, rapid response, easy operation, simplicity, etc. In this case, noble metal nanomaterials, especially Au-based nanomaterials, have attracted attention in electrode modification because of higher catalytic activity, facile mass transfer, and broad active area for determining nitrite. This review is based on the state-of-the-art, which includes a variety of nanomaterials that have been coupled with AuNPs for the creation of nanocomposites, and the construction as well as development of electrochemical sensors for nitrite detection over the last few years (2016-2022). A background study on synthesizing different morphological AuNPs and nanocomposites has also been introduced. The fabrication methods and sensing capabilities of modified electrodes are given special consideration.

A Critical Review of Analytical Applications of Chitosan as a Sustainable Chemical with Functions Galore

Biomass and biowastes stand as sustainable and cost-effective environmentally benign alternative feedstock. Chitosan is a biocompatible, bioactive, and biodegradable biopolymer derived from chitin to achieve eight aspects out of the 12 green chemistry principles. Chitosan got significant attention in several fields including chemical analysis, in addition to chemical functionally, which enabled its use as adsorbent and its structural crosslinking using various crosslinkers. The physicochemical, technological, and optical properties of chitosan have been extensively exploited in analysis. Mainly, deacetylation degree and molecular weight are controlling its properties and hence controlling its functions. This review presents a structure, properties, and functions relationships of chitosan. It also aims to provide an overview of the different functions that chitosan can serve in each analytical technique such as supporting matrix, catalyst…etc. The contribution of chitosan in improving the ecological performance is discussed in each technique.

A Review on Carbon Quantum Dot Based Semiconductor Photocatalysts for the Abatement of Refractory Pollutants

Photocatalysis is a green approach frequently utilised to eliminate a variety of environmentally hazardous refractory pollutants. Accordingly, the modification of semiconductor photocatalysts with Carbon Quantum Dots (CQDs) is of great importance for the treatment of such pollutants due to their attractive physical and chemical properties. CQDs are a perfect candidate to handle photocatalysts of high-performance since they operate as co-catalysts and as visible light harvesters. The higher separation rate of electron-hole pairs in the photocatalytic system is attributable to better photodegradation efficiency. This review classifies CQD based photocatalysts as pure, doped and composite materials and discusses the specific advantages of CQDs in visible light-driven photocatalysis. In this work, the versatile roles of CQDs in CQD-based photocatalytic systems are thoroughly discussed and s u mmarised.

Carbon dots: a novel platform for biomedical applications

Carbon dots (CDs) are a recently synthesised class of carbon-based nanostructures known as zero-dimensional (0D) nanomaterials, which have drawn a great deal of attention owing to their distinctive features, which encompass optical properties (e.g., photoluminescence), ease of passivation, low cost, simple synthetic route, accessibility of precursors and other properties. These newly synthesised nano-sized materials can replace traditional semiconductor quantum dots, which exhibit significant toxicity drawbacks and higher cost. It is demonstrated that their involvement in diverse areas of chemical and bio-sensing, bio-imaging, drug delivery, photocatalysis, electrocatalysis and light-emitting devices consider them as flawless and potential candidates for biomedical application. In this review, we provide a classification of CDs within their extended families, an overview of the different methods of CDs preparation, especially from natural sources, i.e., environmentally friendly and their unique photoluminescence properties, thoroughly describing the peculiar aspects of their applications in the biomedical field, where we think they will thrive as the next generation of quantum emitters. We believe that this review covers a niche that was not reviewed by other similar publications.

Carbon dots synthesized from microorganisms and food by-products: active and smart food packaging applications

Nanotechnology is rapidly becoming a commercial reality for application in food packaging. In particular, the incorporation of nanoparticles into packaging materials is being used to increase the shelf life and safety of foods. Carbon dots (C-dots) have a diverse range of potential applications in food packaging. They can be synthesized from environmentally friendly sources such as microorganisms, food by-products, and waste streams, or they may be generated in foods during normal processing operations, such as cooking. These processes often produce nitrogen- and sulfur-rich heteroatom-doped C-dots, which are beneficial for certain applications. The incorporation of C-dots into food packaging materials can improve their mechanical, barrier, and preservative properties. Indeed, C-dots have been used as antioxidant, antimicrobial, photoluminescent, and UV-light blocker additives in food packaging materials to reduce the chemical deterioration and inhibit the growth of pathogenic and spoilage microorganisms in foods. This article reviews recent progress on the synthesis of C-dots from microorganisms and food by-products of animal origin. It then highlights their potential application for the development of active and intelligent food packaging materials. Finally, a discussion of current challenges and future trends is given.

Chitosan and κ-carrageenan-derived nitrogen and sulfur co-doped carbon dots "on-off-on" fluorescent probe for sequential detection of Fe3+ and ascorbic acid

This study develops a high sensitive and selective "on-off-on" fluorescent probe for sequential detection of iron ion (Fe³⁺) and ascorbic acid (AA) based on nitrogen and sulfur co-doped carbon dots (N, S-CDs), which were synthesized by using chitosan and κ-carrageenan as raw materials through one-step hydrothermal protocol. The synthesized N,S-CDs possess particularly high quantum yield (QY = 59.31%), excellent stability and excitation dependent behavior, showing great potential for practical applications. Furthermore, N,S-CDs provided high selectivity and strong anti-interference to Fe³⁺ due to its fluorescence quenching performance, revealing a wide linear concentration range from 1 to 100 μM for the detection of Fe³⁺ ion with an extremely low limit of detection of 57 nM, and presented reliable and accurate results in actual sample detection of Fe³⁺. The overall fluorescence quenching mechanism of N,S-CDs with Fe³⁺ was due to the formation of N,S-CDs/Fe³⁺ initiated to the aggregation and electron transfer of N,S-CDs, resulting in the static quenching of fluorescence. More interestingly, AA could reduce Fe³⁺ to Fe²⁺ and efficaciously recover the quenched fluorescence of N,S-CDs/Fe³⁺. N,S-CDs/Fe³⁺ as "turn-on" fluorescent probe was further applied for detecting AA in a linear range of 0.5-90 μM with a detection limit of 38 nM.

The synthesis and efficiency investigation of a boronic acid-modified magnetic chitosan quantum dot nanocomposite in the detection of Cu2+ ions

We prepared the magnetic chitosan carbon quantum dot nanoparticles (Fe₃O₄@CQD NPs) via the hydrothermal treatment of chitosan biopolymer and then its magnetization with Fe₃O₄ nanoparticles. (4-Acetylphenyl)boronic acid compound was utilized for the modification of surface of Fe₃O₄@CQD nanoparticles via the covalent imine bond formation between NH₂ groups of chitosan quantum dot with carbonyl functional of acetyl-substituted arylboronic acid. The synthesized Fe₃O₄@CQD@AP-B(OH)₂ was characterized by FE-SEM, EDS, XRD, VSM and ICP-OES analysis and its fluorescence property was studied. This magnetic multifunctional nanoplatform sensor has shown high potential sensitivity for Cu²⁺ ions (in the range of 1.0-30.0 μM with limit of detection 0.3 μM) through interaction of cupric ions with the boronic-acid moiety.

Current advances in bio-fabricated quantum dots emphasising the study of mechanisms to diversify their catalytic and biomedical applications

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

Urea-doped carbon dots as fluorescent switches for the selective detection of iodide ions and their mechanistic study

A facile and green strategy for the fabrication of fluorescent urea-doped carbon dots (N-CDs) has been explored. Significantly, the fluorescent N-CDs could recognize iodide ions (I-) with high selectivity, and their photoluminescence could be efficiently quenched by the addition of I-. The sensitivity analysis for I- indicated a linear relationship in the range from 12.5 to 587 μM with the detection limit as low as 0.47 μM. Furthermore, the I- induced fluorescence (FL) quenching mechanism was investigated employing a combination of techniques, including UV-vis/fluorescence spectroscopy, Density Functional Theory (DFT) calculation, TEM and time-resolved fluorescence decay measurements. The DFT calculation results demonstrated that the amino- and amide groups of N-CDs play a significant role in iodide recognition through the formation of multiple N-H⋯I-, C-H⋯I- and C([double bond, length as m-dash]O)N-H⋯I- interactions with I-. The TEM experiment confirmed the aggregation process when I- was added to the N-CDs solution. Moreover, the radiative decay rate of N-CDs, which was first measured and reported the kinetic behaviors of the FL-quenching process, decreased from 3.30 × 107 s-1 to 1.95 × 107 s-1 after the coordination with I- ions. The reduced lifetime demonstrated that the excited energy dissipation led to a dynamic quenching process. Therefore, such carbon materials can function as effective fluorescent switches for the selective detection of I- ions.

Technical textiles modified with immobilized carbon dots synthesized with infrared assistance

Carbon quantum dots "CQDs" were investigated as photo-luminescent nanomaterials as it advantageous with nontoxicity to be alternative for metallic-nanomaterials in different purposes. Therefore, the presented report demonstrates an innovative strategy for industrialization of antimicrobial/fluorescent cotton textiles via exploitation of "CQDs". Unique/novel infrared-assisted technique was currently investigated for clustering "CQDs" form carboxymethyl cellulose. The successive nucleation of "CQDs" (8.0 nm) was affirmed via infra-red, Raman spectroscopy, NMR, TEM and Zeta-potential analysis. The clustered "CQDs" showed antimicrobial and fluorescent characters. The minimal inhibition concentration for "CQDs" (100 mg/mL) against E. coli and C. albicans showed pathogenic reduction of 96% and 82%, respectively. Fluorescent emission spectra for "CQDs" showed two intense peaks at 415-445 nm. "CQDs" were loaded upon pristine and cationized cotton to prepare CQDs@cotton and CQDs@cationized cotton. While, their physical/mechanical properties (air and water vapor permeabilities, tensile strength and elongation %) and thermal stability (TGA & DTG analysis) were studied. The CQDs@cationized cotton exhibited excellent antimicrobial activity with good durability as after ten repretitive washings, inhibition zone diameter against E. coli, was diminished from 21.0 mm to 14.0 mm. The fluorescent emmision intensity was diminished from 741 to 287 after 10 washing cycles. The produced cotton fabrics could be safely used in the medical and military textiles.

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.

Chitosan-derived N-doped carbon dots for fluorescent determination of nitrite and bacteria imaging

N-doped carbon dots (N-CDs) were successfully synthesized via simple one-step hydrothermal carbonization using chitosan as carbon and nitrogen sources. The obtained N-CDs contained a variety of functional groups on the NCDs surface, and exhibited excitation-independent behavior and strong blue fluorescence with a relatively higher fluorescence quantum yield (QY = 35%). It also presented excellent water solubility, resistance to pH change, high ion strength and UV irradiation. Since the fluorescence of the N-CDs could be selectively quenched by NO₂^-, they could act as a fluorescent sensor for the determination of NO₂^- in real tap water and lake water samples with a wide linear range (1-500 μM) and low detection limit (0.1 μM). They could also be used for bacterial imaging as multicolor fluorescent probes. The results indicated that N-CDs could be a promising candidate material for biomedical applications.

Environmentally exploitable biocide/fluorescent metal marker carbon quantum dots

Carbon quantum dots are currently investigated to act as safe/potent alternatives for metal-based nanostructures to play the role of probes for environmental applications owing to their low toxicity, low cost, chemical inertness, biocompatibility and outstanding optical properties. The synthesis of biocide/fluorescent metal marker carbon quantum dots with hydrophilic character was performed via a quite simple and green technique. The natural biopolymer that was used in this study for the synthesis of carbon quantum dots is fragmented under strong alkaline conditions. Afterwards, under hydrothermal conditions, re-polymerization, aromatization and subsequent oxidation, the carbonic nanostructures were grown and clustered. Dialysis of the so-produced carbonic nanostructures was carried out to obtain highly purified/mono-dispersed carbon quantum dots with a size distribution of 1.5-6.5 nm. The fluorescence intensity of the synthesized carbon quantum dots under hydrothermal conditions for 3 h was affected by dialysis, however, the fluorescence intensity was significantly increased ca. 20 times. The synthesized carbon quantum dots were exploited as fluorescent markers in the detection of Zn2+ and Hg2+. The prepared carbon quantum dots also exhibited excellent antimicrobial potency against Bacillus cereus, Escherichia coli and Candida albicans. The detected minimal inhibitory concentration for the dialyzed CQDs towards the tested pathogens was 350-450 μL mL-1. The presented approach is a simple and green technique for the scaled-up synthesis of biocide/fluorescent marker carbon quantum dots instead of metal-based nanostructures for environmental applications, without using toxic chemicals or organic solvents.

The Use of Carbon Quantum Dot as Alternative of Stannous Chloride Application in Radiopharmaceutical Kits

Even today, technetium-99m is a radionuclide choice for diagnostic in nuclear medicine. The unique chemical and physical properties of technetium-99m make it suitable as an available radionuclide in many centers. In this study, we examined the potential of CQD as a reducing agent in the MDP kit. Citric acid-derived CQD was synthesized and confirmed by FT-IR, TEM, UV-Vis, XPS, and surface analysis. No cytotoxicity was observed by the MTT assay. They were reducing properties of the CQD confirmed by fluorescence microscopy. The MDP kit is prepared by evaluating different parameters that affect the radiolabeling yield, including ligand, time, and CQD. The optimum amount of each parameter is obtained by Box–Behnken software. Finally, fluorescent spectroscopy, SPECT imaging, and biodistribution study showed that CQD reduces technetium-99m. Accumulation of radiotracer in the femur showed that CQD could be used in a radiopharmaceutical kit.

Fluorescent Carbon Dots Derived from Vehicle Exhaust Soot and Sensing of Tartrazine in Soft Drinks

Recycling of waste into valuable products plays a significant role in sustainable development. Herein, we report the conversion of vehicle exhaust waste soot into water-soluble fluorescent carbon dots via a simple acid refluxion method. The obtained carbon dots were characterized using microscopic and spectroscopic techniques. Microscopic techniques reveal that the prepared carbon material is spherical in shape with an average particle size of ∼4 nm. Spectroscopic studies exhibited that the carbon dots are emissive in nature, and the emission is excitation-dependent. Further, the prepared carbon dots were successfully utilized as a fluorescent probe for the detection of tartrazine with a limit of detection of 26 nM. The sensitivity of carbon dots has also been realized by the detection of trace amounts of tartrazine in commercial soft drinks. Overall, this work demonstrates the conversion air pollutant soot into value-added fluorescent nanomaterials toward sensing applications.

Label-free iodide detection using functionalized carbon nanodots as fluorescent probes

A label-free fluorescent nanoprobe for iodide ion (I^-) detection was developed based on the direct fluorescence quenching of spermine-functionalized carbon dots (SC-dots), whether in complex biological fluids or living cells. The positively charged SC-dots were fabricated via one-step microwave synthesis and exhibited excellent optical properties. Due to the strong quenching ability of I^-, SC-dots were utilized for I^- detection with high sensitivity and excellent selectivity, which offered a relatively low detection limit of 0.18 μM. This strategy was also successfully applied for I^- detections in human serum and HeLa cells. The detection process is facile, highly sensitive and selective, providing a new insight into the potential applications of SC-dots for anion nanoprobe designs in clinical diagnosis and other biologically related areas. Graphical abstract.

Facile Synthesis of Nitrogen-Doped Carbon Quantum Dots with Chitosan for Fluorescent Detection of Fe3

A facile, economical, and one-step hydrothermal method was used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) with chitosan as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 2 nm and exhibit excitation wavelength-dependent fluorescence with a maximum excitation and emission at 330 and 410 nm, respectively. Furthermore, due to the effective quenching effect of Fe³⁺ ions, the prepared N-CQDs can be used as a fluorescent sensor for Fe³⁺ ion-sensitive detection with a detection limit of 0.15 μM. The selectivity experiments revealed that the fluorescent sensor is specific to Fe³⁺ even with interference by high concentrations of other metal ions. Most importantly, the N-CQD-based Fe³⁺ ion sensor can be successfully applied to the determination of Fe³⁺ in real water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for the monitoring of Fe³⁺ in environmental application.

Nanomaterials-Based Colorimetric Immunoassays

Colorimetric immunoassays for tumor marker detection have attracted considerable attention due to their simplicity and high efficiency. With the achievements of nanotechnology and nanoscience, nanomaterials-based colorimetric immunoassays have been demonstrated to be promising alternatives to conventional colorimetric enzyme-linked immunoassays. This review is focused on the progress in colorimetric immunoassays with the signal amplification of nanomaterials, including nanomaterials-based artificial enzymes to catalyze the chromogenic reactions, analyte-induced aggregation or size/morphology change of nanomaterials, nanomaterials as the carriers for loading enzyme labels, and chromogenic reactions induced by the constituent elements released from nanomaterials.

Chitosan-Based Carbon Quantum Dots for Biomedical Applications: Synthesis and Characterization

Rapid development in medicine and pharmacy has created a need for novel biomaterials with advanced properties such as photoluminescence, biocompability and long-term stability. The following research deals with the preparation of novel types of N-doped chitosan-based carbon quantum dots. Nanomaterials were obtained with simultaneous nitrogen-doping using biocompatible amino acids according to Green Chemistry principles. For the carbon quantum dots synthesis chitosan was used as a raw material known for its biocompability. The nanomaterials obtained in the form of lyophilic colloids were characterized by spectroscopic and spectrofluorimetric methods. Their quantum yields were determined. Additionally the cytotoxicity of the prepared bionanomaterials was evaluated by XTT (2,3-Bis-(2-methoxy-4-nitro5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt) method. Our results confirmed the formation of biocompatible quantum dots with carbon cores exhibiting luminescence in visible range. Performed studies showed that modification with lysine (11.5%) and glutamic acid (7.4%) had a high impact on quantum yield, whereas functionalization with amino acids rich in S and N atoms did not significantly increase in fluorescence properties. XTT assays as well as morphological studies on human dermal fibroblasts confirmed the lack of cytotoxicity of the prepared bionanomaterials. The study shows chitosan-based quantum dots to be promising for biomedical applications such as cell labelling, diagnostics or controlled drug delivery and release systems.