Green synthesized carbon quantum dots from Prosopis juliflora leaves as a dual off-on fluorescence probe for sensing mercury (II) and chemet drug

A facile synthesis of water-soluble copper nanoclusters as label-free fluorescent probes for rapid, selective and sensitive determination of alizarin red

Copper nanoclusters (FA@CuNCs) emitting blue fluorescence were successfully developed via a one-pot technique. In this method, the copper chloride, folic acid and hydrazine hydrate were applied as a precursor, protective agent and reducing agent, respectively. The absorption, fluorescence excitation and emission spectra of FA@CuNCs were carried out by using ultraviolet-visible and fluorescence spectrometry, respectively. The morphology, particle size, functional groups, oxidation states of elements of FA@CuNCs were discussed via using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stability of FA@CuNCs was studied under various conditions, such as storage time at 25 ℃, ultraviolet radiation time, sodium chloride solutione and pH. The FA@CuNCs displayed blue fluorescence under the excitation wavelength of 361 nm, and the fluorescence quantum yield was 7.45 %. As a result of the inner filter effect, the alizarin red could significantly weaken the blue fluorescence of FA@CuNCs. Thus, the as-prepared FA@CuNCs could be utilized as fluorescence nanosensors for the trace determination of alizarin red. This platform suggested an excellent linear range for alizarin red varying from 0.5 to 200 μM with a fitting coefficient of 0.9955. The detection limit was calculated to be 0.064 μM in the light of the 3b/k (b and k refer to the standard deviation and slope of fitted curve, respectively). Furthermore, the as-developed FA@CuNCs could be used to detect the alizarin red in real samples and for the sensing of temperature.

Progress and obstacles in employing carbon quantum dots for sustainable wastewater treatment

We explored the potential of carbon quantum dots (CQDs) as novel materials for wastewater treatment and their role towards environmental sustainability. The advantages of CQDs over other carbon-based materials, when synthesized using the same precursor material and for the same contaminant are discussed, enabling future researchers to choose the appropriate material. CQDs have demonstrated exceptional adaptability in various wastewater treatment, acting as efficient adsorbents for contaminants, exhibiting excellent photocatalytic properties for degradation of organic pollutants, and functioning as highly sensitive sensors for water quality monitoring. We found that bottom-up approach has better control over particle size (resulting CQDs: 1-4 nm), whereas top-down synthesis approach (resulting CQDs: 2-10 nm) have more potential for large scale applications and tunability. Transmission electron microscopy (TEM) remains the most expensive characterization technique, which provides the best resolution of the CQD's surface. The study emphasizes on the environmental impact and safety considerations pertaining to CQDs by emphasizing the need for thorough toxicity evaluation, and necessary environmental precautions. The study also identifies the lacunae pertaining to critical challenges in practical implementation of CQDs, such as scalability, competition of co-existing contaminants, and stability. Finally, future research directions are proposed, advocating green synthesis approaches, tailored surface functionalization, and, lowering the overall cost for analysis, synthesis and application of CQDs.

Facile Green Gamma Irradiation of Water Hyacinth Derived-Fluorescent Carbon Dots Functionalized Thiol Moiety for Metal Ion Detection

Fluorescent sensor-based carbon dots (CDs) have significantly developed for sensing metal ions because of their great physical and optical properties, including tunable fluorescence emission, high fluorescence quantum yield, high sensitivity, non-toxicity, and biocompatibility. In this research, a green synthetic approach via simple gamma irradiation for the carbon dot synthesis from water hyacinth was developed since water hyacinth has been classified as an invasive aquatic plant containing cellulose, hemicellulose, and lignin. The thiol moiety (SH) was further functionalized on the surface functional groups of CDs as the "turn-off" fluorescent sensor for metal ion detection. Fluorescence emission displayed a red shift from 451 to 548 nm when excited between 240 and 500 nm. The quantum yield of CDs-SH was elucidated to be 13%, with strong blue fluorescence emission under ultraviolet irridiation (365 nm), high photostability and no photobleaching. The limit of detection was determined at micromolar levels for Hg2+, Cu2+, and Fe3+. CDs-SH could be a real-time monitoring sensor for Hg2+ and Cu2+ as fluorescence quenching was observed within 2 min. Furthermore, paper test-strip based CDs-SH could be applied to detect these metal ions.

Visible Light Enhancement of Biocarbon Quantum-Dot-Decorated TiO2 for Naphthalene Removal

In this study, carbon-quantum-dot (CQD)-decorated TiO2 was prepared using an ultrasonic doping method and applied in the photocatalytic degradation of naphthalene under sunlight irradiation. The CQDs were synthesized from a typical macroalgae via diluted sulfuric acid pretreatment and hydrothermal synthesis using an optimal design, i.e., 3 wt% and 200 °C, respectively. The CQD/TiO2 composite remarkably enhanced the photocatalytic activity. The degradation of naphthalene under a visible light environment indicated that there is a synergistic mechanism between the CQDs and TiO2, in which the generation of reactive oxygen species is significantly triggered; in addition, the N that originated from the macroalgae accelerated the photocatalytic efficiency. Kinetic analysis showed that the photocatalytic behavior of the CQD/TiO2 composite followed a pseudo-first-order equation. Consequently, our combined experimental approach not only provides a facile pretreatment process for bio-CQDs synthesis, but also delivers a suitable TiO2 photocatalyst for the visible environment along with critical insights into the development of harmful macroalgae resources.

Turn-Off Fluorescence Sensor for the Detection of Ferric Ion in Water Using Green Synthesized Wrightia coccinea Carbon Quantum Dot

The current study report that the production of carbon quantum dots from Wrightia coccinea (WC) leaves using an eco-friendly, one-pot process. The structural, morphological, and optical characteristics of the CDs made from W. coccinea leaves by hydrothermal treatment at 200 °C for six hours were assessed using a variety of spectroscopic and electron microscopy techniques. The average size of CD was found to be approximately 5 nm using transmission electron microscopy (TEM) and the quantum yield of the produced CD was 15.6%. The synthesized CDs demonstrated extraordinary sensing capacity with a detection limit of 0.511 µM for ferric ion detection. The impact of varying pH levels on the fluorescence behavior of CD was thoroughly investigated. The maximum fluorescence intensity was examined at pH 3. Therefore, to detect Fe3+ ions as best as possible, the pH of the entire solution was adjusted to a value of 3. Furthermore, the pH-dependent fluorescence feature of CDs can be exploited by pH-sensitive fluorescence sensors. In the future, this might provide an added advantage for pH-based fluorescence sensor applications.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Yellow-emitting carbon dots as fluorescent sensors for the rapid determination of curcumin

The non-standard use of curcumin could cause some adverse drug reactions, such as diarrhea, nausea and skin allergies. Thus, the curcumin determination was fundamental to disease treatment and prevention. Herein, a facile and efficient fluorescent probe was developed based on carbon dots, which was prepared through hydrothermal method (o-phenylenediamine and N-isopropylacrylamide as the reaction raw materials). Characteristics of the as-fabricated carbon dots (NCDs) were studied through some analysis techniques, such as UV-vis absorption spectroscopy, transmission electron microscopy, Fourier transform infrared instrument, X-ray photoelectron spectroscopy and fluorescence spectrophotometer. Fluorescence quenching phenomenon could be observed after addition of curcumin. This as-prepared fluorescent probe displayed a significant response for the determination of curcumin with a satisfactorily lower detection limit of 0.017 μM and a considerable linear range of 0.5-50 μM compared to reported literatures. Because of the preeminent repeatability and anti-jamming capability, the as-developed CDs suggested mighty potentiality for actual applications of curcumin detection in real samples and temperature sensing.

Lavandula multifida as a novel eco-friendly fluorescent-blue material for mercury ions sensing in seawater at femto-molar concentration

In this paper, we present a novel fluorescent material based on the herbal tea of Lavandula multifida (Lm). The fluorescence properties of Lm aqueous extract were analyzed under various excitation wavelengths in the range of 290-450 nm. The Lm herbal infusion was found to be highly fluorescent, with an emission maximum at 450 nm under excitation at 390 nm. Consequently, it was exploited to develop a fluorescence method for detecting metal ions. Results obtained upon the addition of Hg2+, Na+, K+, Ca2+, Mg2+, Pb2+, Cd2+, Cu2+, Ni2+, Bi3+, Mn2+, Fe3+ and Co2+ ions showed that the fluorescence intensity of the Lm aqueous extract decreased strongly with the presence of mercury ions. A solid-state fluorescent sensor, based on Lm embedded into a Nafion membrane and deposited on a transparent polyethylene terephthalate (PET) sheet, has also been developed for the effective detection of Hg2+ ions. The Lm-Nafion-PET sensor exhibited good stability, high repeatability, and reproducibility. Furthermore, the Lm-Nafion/PET sensor demonstrated remarkable sensitivity to Hg2+ in sea water, with a limit of detection of 0.25 fM. To our knowledge, this is the first study which reports Lavandula multifida plant for making a novel eco-friendly fluorescent solid-state sensor for the detection of mercury ions at femto-molar concentrations in seawater.

Carbon nanoprobe derived from Nyctanthes arbor-tristis flower: Unveiling the surface defect-derived fluorescence

Dual Emissive (green and blue) Carbon dots (C-Dots) aka g-CD and b-CD were synthesized using flowers of Nyctanthes arbortristis as the sole precursor via hydrothermal method without the aid of any external passivating agent. In the present report, the effect of time and temperature on the hydrothermal reaction was evaluated in order to modulate the surface defects that could lead to dual emissions. To gauge the nature, size, morphology, and optoelectronic characteristics, the C-Dots were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and Fluorescence spectroscopy. The fluorescence studies of both the Carbon Dots revealed their excitation-dependent emission characteristics with the bathochromic shift. Furthermore, both g-CD and b-CD could effectively be utilized as efficient fluorescent probes for the selective and sensitive detection of Fe3+. These fluorescent nanoprobes could selectively detect Fe3+ over a wide range of concentrations (3 µM to 100 µM) with limit of detection (LOD) as low as 0.06 µM and 0.70 µM respectively. These tuneable Carbon Dots having wider solubilities would open a new avenue as Nanosensors for real-time applications.

Gold nanoparticles embedded Fe-BTC (AuNPs@Fe-BTC) metal-organic framework as a fluorescence sensor for the selective detection of As(III) in contaminated waters

In this article, a new off-mode fluorescent platform based on the metal-organic framework (MOF) is introduced as a highly selective and rapid chemical sensor for the detection of As(III) in water and wastewater samples. A typical Fe-BTC (BTC = 1,3,5-benzenetricarboxylate or trimesic acid) MOF was used as a porous template for loading gold nanoparticles (AuNPs@Fe-BTC MOF). The physicochemical properties of AuNPs@Fe-BTC MOF were characterized by Fourier-transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EAX), element mapping (MAP) and X-ray diffraction (XRD) analysis. This sensing method for As(III) ions is based on the fact that the fluorescence intensity of AuNPs@Fe-BTC MOF sensor decreases in proportion to the increase in As(III) concentration. The main effective factors on the performance of the sensor signal such as MOF dosage, sonication time, pH and reaction time were optimized. Under optimized conditions, the calibration graph was linear in the concentration range of 0.5-380 ng mL-1 of As(III) and the limit of detection was 0.2 ng mL-1. The proposed method was successfully validated by addition/recovery experiments by the determination of As(III) in four river water and two wastewater effluent samples.

One Pot Hydrothermal Synthesis and Application of Bright-yellow-emissive Carbon Quantum Dots in Hg2+ Detection

Carbon quantum dots (CQD) have drawn great interest worldwide for their extensive application as sensors due to their extraordinary physical and chemical characteristics, good biocompatibility, and high fluorescence in nature. Here, we demonstrate a technique for detecting mercury (Hg2+) ion using a fluorescent CQD probe. Ecology is concerned about the accumulation of heavy metal ions in water samples due to their harmful effects on human health. Sensitive identification and removal of metal ions from water samples are required to reduce heavy metals' risk. To find out Mercury in the water sample, carbon quantum dots were used and synthesized by 5-dimethyl amino methyl furfuryl alcohol and o-phenylene diamine through the hydrothermal technique. The synthesized CQD shows yellow emission when exposed to UV irradiation. Mercury ion was used to quench carbon quantum dots, and it was found that the detection limit was 5.2 nM with a linear range of 15-100 µM. The synthesized carbon quantum dots were demonstrated to efficiently detect Mercury ions in real water samples.

Progress on the luminescence mechanism and application of carbon quantum dots based on biomass synthesis

With the continuous development of carbon-based materials, a variety of new materials have emerged one after another. Carbon Quantum Dots (CQDs) have succeeded in standing out from the crowd of new materials due to their better optical properties in biomedicine, ion detection, anti-counterfeiting materials and photocatalysis. In recent years, through the continuous exploration of CQDs, research scholars have found that the organic substances or heavy metals contained in traditional ones can cause irreversible harm to people and the environment. Therefore, the application of traditional CQDs in future studies will be gradually limited. Among various new materials, biomass raw materials have the merits of good biocompatibility, lower toxicity and green and environmental protection, which largely overcome the defects of traditional materials and have attracted many scholars to focus on the research and development of various biomass CQDs. This paper summarises the optical properties, fluorescence mechanisms, synthetic methods, functionalisation modulation of biomass CQDs and their relevant research progress in the fields of ion detection, bioimaging, biomedicine, biosensing, solar cells, anti-counterfeit materials, photocatalysis and capacitors. Finally, the paper concludes with some discussion of the challenges and prospects of this exciting and promising field of application.

Nanostructures for prevention, diagnosis, and treatment of viral respiratory infections: from influenza virus to SARS-CoV-2 variants

Viruses are a major cause of mortality and socio-economic downfall despite the plethora of biopharmaceuticals designed for their eradication. Conventional antiviral therapies are often ineffective. Live-attenuated vaccines can pose a safety risk due to the possibility of pathogen reversion, whereas inactivated viral vaccines and subunit vaccines do not generate robust and sustained immune responses. Recent studies have demonstrated the potential of strategies that combine nanotechnology concepts with the diagnosis, prevention, and treatment of viral infectious diseases. The present review provides a comprehensive introduction to the different strains of viruses involved in respiratory diseases and presents an overview of recent advances in the diagnosis and treatment of viral infections based on nanotechnology concepts and applications. Discussions in diagnostic/therapeutic nanotechnology-based approaches will be focused on H1N1 influenza, respiratory syncytial virus, human parainfluenza virus type 3 infections, as well as COVID-19 infections caused by the SARS-CoV-2 virus Delta variant and new emerging Omicron variant.

Preparation of carbon quantum dots from ionic liquid modified biomass for the detection of Fe3+ and Pd2+ in environmental water

A new type of green carbon quantum dots (ILB-CQDs) was prepared by hydrothermal method using ionic liquid as a modifier and grape skin as carbon source, and was obtained from hydrogen-bonded lattice structure ionic liquid preparation, which makes the CQDs in a ring-like stable structure with a stability period of more than 90 day. There is also the catalytic effect of the ionic liquid on cellulose, which makes the prepared CQDs show good advantages, such as uniform particle size, high quantum yield (26.7%), and very good fluorescence performance. This is a smart material for the selective detection of Fe³⁺ and Pd²⁺. It has a detection limit of 0.001 nM for Fe³⁺ and 0.23 µM for Pd²⁺ in pure water. It has a detection limit of 3.2 nmol/L for Fe³⁺ and 0.36 µmol/L for Pd²⁺ in actual water, both of which meet the requirements of WHO drinking water standards. And there is to achieve more than 90% of water restoration effect.

Colorimetric and Fluorescent Sensing of Copper Ions in Water through o-Phenylenediamine-Derived Carbon Dots

Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using a simple one-step hydrothermal method starting from o-phenylenediamine (OPD) and ammonium sulfide. The prepared NSCDs presented a selective dual optical response to Cu(II) in water through the arising of an absorption band at 660 nm and simultaneous fluorescence enhancement at 564 nm. The first effect was attributed to formation of cuprammonium complexes through coordination with amino functional groups of NSCDs. Alternatively, fluorescence enhancement can be explained by the oxidation of residual OPD bound to NSCDs. Both absorbance and fluorescence showed a linear increase with an increase of Cu(II) concentration in the range 1-100 µM, with the lowest detection limit of 100 nM and 1 µM, respectively. NSCDs were successfully incorporated in a hydrogel agarose matrix for easier handling and application to sensing. The formation of cuprammonium complexes was strongly hampered in an agarose matrix while oxidation of OPD was still effective. As a result, color variations could be perceived both under white light and UV light for concentrations as low as 10 µM. Since these color changes were similarly perceived in tap and lake water samples, the present method could be a promising candidate for simple, cost-effective visual monitoring of copper onsite.

Reversible detection of Hg(II) in pure water based on thymine modified nitrogen, sulfur co-doped carbon dots combined with antidote

Conventional Hg²⁺ visual sensors are unsustainable, hindering their practical application for improved water quality and health. In order to address this challenge, herein, N, S co-doped carbon nanodots (NS-CDs) were prepared and well characterized, presented the fluorescent monitoring for Hg²⁺ over other metal ions with the limit of detection (LOD) of 0.47 µM. Next, the CDs were successfully modified by thymine without any fluorescence labelling (referred to as T-NS-CDs). The sensitivity to Hg²⁺ cloud be noticeable enhanced due to the formation of T-Hg²⁺-T specific base pairs. Accordingly, the LOD was calculated with values as low as 1.56 nM. Furthermore, Hg²⁺ could be released and complexed with antidote (meso-2,3-dimercaptosuccinic acid) (DMSA-Hg²⁺), being the responsible for the reversible interconversion between T-Hg²⁺-T and DMSA-Hg²⁺. Interestingly, the proposed sensing system also applies to the fluorescent sensing for Hg²⁺ in tap water with satisfactory recoveries (96.97 %-101.38 %, RSD < 2 %). Thus, by simply combination of elemental doping and surface functionalization, the surface state and functionalities of CDs could be tailorable, endowing the fluorometric sensing towards Hg²⁺ in environmental system.

The Consequences of Water Interactions with Nitrogen-Containing Carbonaceous Quantum Dots-The Mechanistic Studies

Despite the importance of quantum dots in a wide range of biological, chemical, and physical processes, the structure of the molecular layers surrounding their surface in solution remains unknown. Thus, knowledge about the interaction mechanism of Nitrogen enriched Carbonaceous Quantum Dots' (N-CQDs) surface with water-their natural environment-is highly desirable. A diffusive and Stern layer over the N-CQDs, characterized in situ, reveals the presence of anionic water clusters [OH(H₂O)_n]^-. Their existence explains new observations: (i) the unexpectedly low adsorption enthalpy (ΔH_ads) in a pressure range below 0.1 p/p_s, and ΔH_ads being as high as 190 kJ/mol at 0.11 p/p_s; (ii) the presence of a "conductive window" isolating nature-at p/p_s below 0.45-connected to the formation of smaller clusters and increasing conductivity above 0.45 p/p_s, (iii) Stern layer stability; and (iv) superhydrophilic properties of the tested material. These observables are the consequences of H₂O dissociative adsorption on N-containing basic centers. The additional direct application of surfaces formed by N-CQDs spraying is the possibility of creating antistatic, antifogging, bio-friendly coatings.

Recent advances in green carbon dots (2015-2022): synthesis, metal ion sensing, and biological applications

Carbon dots (CDs) show extensive potential in various fields such as sensing, bioimaging, catalysis, medicine, optoelectronics, and drug delivery due to their unique properties, that is, low cytotoxicity, cytocompatibility, water-solubility, multicolor wavelength tuned emission, photo-stability, easy modification, strong chemical inertness, etc. This review article especially focuses on the recent advancement (2015-2022) in the green synthesis of CDs, their application in metal ions sensing and microbial bioimaging, detection, and viability studies as well as their applications in pathogenic control and plant growth promotion.

Green synthesis of carbon quantum dots and their environmental applications

Green synthesis of scalable, high-quality, fluorescent carbon quantum dots (CQDs) from natural biomass remains attractive due to their outstanding environmental application. CQDs are an emerging class of zero-dimensional carbon nanomaterials (<10 nm) that have recently attracted much attention due to their strong optical properties, biocompatibility, nontoxicity, uniform particle size, high photostability, low-cost synthesis, and highly tunable photoluminescence. The unique properties of CQDs possess a broad range of prospective applications in a number of fields such as metal ions detection, photocatalysis, sensing, medical diagnosis, bioimaging, and drug delivery. CQD nanostructures are synthesized using various techniques such as hydrothermal method, laser ablation, microwave irradiation, electrochemical oxidation, reflux method, and ultrasonication. However, this type of fabrication approach requires several chemical reactions including oxidation, carbonization, and pyrolysis. Green synthesis of CQDs has several advantages such as the use of low-cost and non-toxic raw materials, renewable resources, simple operations, and being environment-friendly. This review article will discuss the physicochemical properties of CQDs techniques used in the production of CQDs, and the stability of CQDs along with their applications in wastewater treatment and biomedical fields.

Ultrasensitive detection of mercury(II) in aqueous solutions via the spontaneous precipitation of CsPbBr3 crystallites

Mercury(II) is one of the most toxic ions and has the lowest allowed concentration in water. Lowering the detection limits of Hg²⁺ based on fluorescence methods is challenging compared to the detection of other heavy metal ions. Co-precipitation of the CsPbBr₃ precursor and mercury ions in aqueous solutions was developed for the ultra-trace level detection of Hg²⁺. It was found that the formed CsPbBr₃ crystals with sizes in the range of nanometers to micrometers exhibited strong fluorescence in the solid state free of water, and the incorporation of Hg²⁺ in the crystals would cause fluorescence quenching. Therefore, the decrease in fluorescence intensity could be used to quantitatively detect Hg²⁺. A microwell array was designed by dispersing the sample solution with the perovskite probe and evaporating water for 3 min to form solid fluorescent crystals, leading to the incorporation of Hg²⁺ in the crystals. This evaporation-induced co-precipitation strategy successfully solved the problem of the instability of perovskite materials in water. The concentration of Hg²⁺ can be obtained according to the decrease in the fluorescence intensity, which is caused by the replacement of Pb²⁺ by Hg²⁺ in the crystals during the crystallization process. The CsPbBr₃ crystallites can be used to detect ultra-trace levels of Hg²⁺ simply and quickly, with a linear range of 5-100 nM and limit of detection (LOD) as low as 0.1 nM. More importantly, no organic molecules are required to prepare crystals since the micron-sized crystals have obvious fluorescence. This method demonstrates great promise in detecting low concentrations of Hg²⁺ in aqueous solutions.

Carbon dots from eco-friendly precursors for optical sensing application: an up-to-date review

Abstract

Carbon dots (CDs) are zero-dimensional quasi-spherical nanoparticles endowed with excellent advantages including good luminescence features, photostability, low cytotoxicity, remarkable aqueous solubility, favourable biocompatibility, low risk to environment and great flexibility in surface modification. Fluorescent CDs that can selectively respond to specific inorganic/organic target molecules in environmental and biological samples are of prime significance amongst the new generation intelligent sensors due to the critical involvement of different ions/molecular species in not only human health, but also in environment processes. In this context, preparation of CDs from bioprecursors has immense significance due to the involvement of green principles, inexpensive, clean, nontoxic, easily accessible, renewable and large-scale production can be realized. This article aims at exploring different types of green raw materials including plant biomass, animal products, food items and waste materials as carbon sources for the synthesis of both undoped and doped CDs. The emphasis is given on different synthetic approaches adopted for improving the quantum yield without any chemical modification, the characterization techniques, mechanistic origin of photoluminescence and fluorescence response mechanisms involved in the sensing action towards various analytes. The significant benefits and limitations of CDs obtained from eco-friendly precursors through green approaches are summarized. Various challenges and the future prospects of these carbonaceous nanomaterials as sensors are also discussed.

Graphical abstract

Double-signal quantification of amoxicillin based on interaction with 4-aminoantipyrine at copper and nitrogen co-doped carbon quantum dots as an artificial nanozyme

An one-pot hydrothermal method was developed for synthesis of carbon quantum dots co-doped with copper and nitrogen (Cu, N@CQDs). The synthesized Cu, N@CQDs has unique advantages such as high fluorescence quantum yield (39.1%) and high catalytic activity. Oxidative coupling of amoxicillin (AMX) with 4-aminoantipyrine (4-NH₂-APE) in the presence of H₂O₂ as an oxidant to produce pink quinoneimine chromogen was carried out with the aid of Cu, N@CQDs as a peroxidase-like catalyst. This system was used for the colorimetric and fluorometric assays of AMX with reliable results. Colorimetric method is based on the measurement of a pink-colored product at λ_max = 505 nm while the fluorometric assay is based on the quenching of the fluorescence emission of Cu, N@CQDs at 440 nm after excitation at 370 nm. For the colorimetric method, the absorption intensity linearly increased over the concentration range 4.3-110.0 µM with LOD (S/N = 3) of 1.3 µM. For the fluorometric method, the emission intensity of Cu, N@CQDs linearly decreased upon addition of AMX in the concentration range 0.2-120.0 µM with a limit of detection (LOD, S/N = 3) of 0.06 µM. The proposed system was applied to the determination of AMX in different real samples such as pharmaceutical capsules, human serum, milk, and conduit water samples with recoveries in the range 95.8-104.1% and relative standard deviation (RSD %) less than 4.1%.

One-Step Green Synthesis of Water-Soluble Fluorescent Carbon Dots and Its Application in the Detection of Cu2

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu²⁺ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu²⁺ ions, with a low detection limit of 0.005 μg/mL; this was largely ascribed to Cu²⁺ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu²⁺ metal ions in wastewater.

A novel fluorescent nano carbon quantum dots derived from Lactarius hatsudake for high selective vitamin B12 detection

BACKGROUND (OBJECTIVE)

A large edible fungus Lactarius hatsudake (Lh) was used as carbon source to produce fluorescent carbon dots (CDs) with high quantum yield and high photostability by one-step hydrothermal method.

METHODS

The structure and optical properties of Lh-CDs were characterized by XRD, XPS, FTIR, and UV-Vis, and the stability of Lh-CDs was studied. The maximum excitation wavelength and emission wavelength of Lh-CDs were 324 and 408 nm, respectively, and the average fluorescence lifetime was 2.29 ns.

RESULTS

The linear range is 0∼20 μM (R2=0.9972) with detection limit of 36.9 nM.

HIGHLIGHTS

At the same time, the mechanism of fluorescence quenching was internal filtration effect.

CONCLUSION

It showed that Lh-CDS had good selectivity, high sensitivity, and good anti-interference ability to VB12, which provided a new detection method for VB12.

Nanodrug Transmembrane Transport Research Based on Fluorescence Correlation Spectroscopy

Although conventional fluorescence intensity imaging can be used to qualitatively study the drug toxicity of nanodrug carrier systems at the single-cell level, it has limitations for studying nanodrug transport across membranes. Fluorescence correlation spectroscopy (FCS) can provide quantitative information on nanodrug concentration and diffusion in a small area of the cell membrane; thus, it is an ideal tool for studying drug transport across the membrane. In this paper, the FCS method was used to measure the diffusion coefficients and concentrations of carbon dots (CDs), doxorubicin (DOX) and CDs-DOX composites in living cells (COS7 and U₂OS) for the first time. The drug concentration and diffusion coefficient in living cells determined by FCS measurements indicated that the CDs-DOX composite distinctively improved the transmembrane efficiency and rate of drug molecules, in accordance with the conclusions drawn from the fluorescence imaging results. Furthermore, the effects of pH values and ATP concentrations on drug transport across the membrane were also studied. Compared with free DOX under acidic conditions, the CDs-DOX complex has higher cellular uptake and better transmembrane efficacy in U₂OS cells. Additionally, high concentrations of ATP will cause negative changes in cell membrane permeability, which will hinder the transmembrane transport of CDs and DOX and delay the rapid diffusion of CDs-DOX. The results of this study show that the FCS method can be utilized as a powerful tool for studying the expansion and transport of nanodrugs in living cells, and might provide a new drug exploitation strategy for cancer treatment in vivo.

Cuttlefish ink-based N and S co-doped carbon quantum dots as a fluorescent sensor for highly sensitive and selective para-nitrophenol detection

Para-nitrophenol (PNP) is an important raw material for organic synthesis and its extensive use has produced a series of environmental problems. Here, we develop a highly sensitive and selective fluorescent detection method for PNP with cuttlefish ink-based carbon quantum dots (CQDs). The cuttlefish ink, which is rich in eumelanin, is utilized as the only precursor to synthesize the CQDs via a one-step hydrothermal method. The resultant CQDs were co-doped with nitrogen and sulfur and exhibited excellent fluorescence properties. Two optimal emissions can be observed at the excitation/emission wavelengths of 320/385 nm and 390/465 nm, respectively. In the presence of PNP, the two emissions are remarkably quenched. PNP can be measured in the linear detection concentration range of 1.25-50 μM (Em = 385 nm and R² = 0.9884) or 1.25-27.5 μM (Em = 465 nm and R² = 0.9818) with a detection limit of 0.05 μM. Significantly, it is found that a much wider linear detection range of 0.05-125 μM with a lower detection limit of 0.039 μM (3σ/k) can be achieved when log(I_{385 nm} + I_{465 nm}) was utilized to quantify PNP. The investigations of the sensing mechanism suggested that the inner filter effect and photoinduced electron transfer of PNP and N,S-CQDs leads to fluorescence quenching. The sensing method is successfully applied for PNP detection in real water samples with satisfactory recoveries (91.18-103.14%). A new sustainable waste-prevention strategy of cuttlefish ink and a feasible alternative to PNP detection methods is provided in this article.

Green synthesis of carbon dots and their applications

Carbon dots (CDs) are nanoparticles with tunable physicochemical and optical properties. Their resistance to photobleaching and relatively low toxicity render them attractive alternatives to fluorescent dyes and heavy metal-based quantum dots in the fields of bioimaging, sensing, catalysis, solar cells, and light-emitting diodes, among others. Moreover, they have garnered considerable attention as they lend themselves to green synthesis methods. Increasingly, one-pot syntheses comprising exclusively of renewable raw materials or renewable refined compounds are gaining favor over traditional approaches that rely on harsh chemicals and energy intensive conditions. The field of green CD synthesis is developing rapidly; however, challenges persist in ensuring the consistency of their properties (e.g., fluorescence quantum yield) relative to conventional preparation methods. This has mostly limited their use to sensing and bioimaging, leaving opportunities for development in optoelectronic applications. Herein, we discuss the most common green CD synthesis and purification methods reported in the literature and the renewable precursors used. The physical, chemical, and optical properties of the resulting green-synthesized CDs are critically reviewed, followed by a detailed description of their applications in sensing, bioimaging, biomedicine, inks, and catalysis. We conclude with an outlook on the future of green CD synthesis. Future research efforts should address the broad knowledge gap between CDs synthesized from renewable versus non-renewable precursors, focusing on discrepancies in their physical, chemical, and optical properties. The development of cost effective, safe, and sustainable green CDs with tunable properties will broaden their implementation in largely untapped applications, which include drug delivery, photovoltaics, catalysis, and more.

A review of the green carbon dot synthesis literature outlining the various precursors used, synthesis and purification methods employed, the resulting physicochemical properties of the carbon dots, and their applications.

Synthesis, Characterization and Ecotoxicity Evaluation of Biochar-Derived Carbon Dots from Spruce Tree, Purple Moor-Grass and African Oil Palm

Biochar-derived C-Dots from Picea, Molinia caerulea and Elaeis guineensis were synthesized through a hydrothermal process, and their physicochemical and optical characteristics and environmental effects were compared. These C-Dots were characterized by techniques such as Attenuated Total Reflection–Fourier Transform Infrared (ATR-FTIR), UV-Vis spectrophotometry, fluorescence spectroscopy, dynamic light scattering (DLS), Z potential, and High-Resolution Transmission Electronical Microscopy (HR-TEM). The ecotoxicity tests were performed using the Microtox™ test, making this study one of the few that use this method. The C-Dots from Molinia caerulea showed the best quantum yield (QY) of 8.39% and moderate ecotoxicity, while Elaeis guineensis has the lowest QY (2.31%) but with zero toxicity. Furthermore, the C-Dots from Picea presents good optical properties but showed high toxicity and limits its use. Finally, all C-Dots showed functional groups that could be biofunctionalized with biomolecules, especially C-Dots from Molinia caerulea and Elaeis guineensis show potential for use in the development of optical biosensors.

Green Route for the Synthesis of Fluorescent Carbon Nanoparticles from Circassian Seeds for Fe(III) Ion Detection

A facile and green strategy was carried out for the preparation of fluorescent carbon nanoparticles (CNp) using non-toxic circassian seeds as carbon precursor (CNp, named ACNp). The surface of amorphous ACNp is latched with different surface moieties such as hydroxyl, carbonyl, ether and amino groups and it is confirmed by FTIR and XPS. These functionalities provide high solubility and stability to ACNp in aqueous medium. The surface of ACNp is highly negatively charged due to the presence of oxygen rich functional groups and it is confirmed by zeta potential. A reasonably good quantum yield (QY) of 5.1% is obtained for ACNp compared to other CNp derived from bioprecursors without any surface passivation. Circassian seeds are self sufficient for the synthesis of N doped CNp. The excitation dependent fluorescence property of ACNp is invariant under ionic and thermal environments. They exhibit good selectivity towards Fe³⁺ ions via static quenching mechanism with detection limit of 32.7 µM.

An Overview of the Recent Developments in Carbon Quantum Dots—Promising Nanomaterials for Metal Ion Detection and (Bio)Molecule Sensing

The fluorescent carbon quantum dots (CQDs) represent an emerging subset of carbonaceous nanomaterials, recently becoming a powerful tool for biosensing, bioimaging, and drug and gene delivery. In general, carbon dots are defined as zero-dimensional (0D), spherical-like nanoparticles with <10 nm in size. Their unique chemical, optical, and electronic properties make CQDs versatile materials for a wide spectrum of applications, mainly for the sensing and biomedical purposes. Due to their good biocompatibility, water solubility, and relatively facile modification, these novel materials have attracted tremendous interest in recent years, which is especially important for nanotechnology and nanoscience expertise. The preparation of the biomass-derived CQDs has attracted growing interest recently due to their low-cost, renewable, and green biomass resources, presenting also the variability of possible modification for the enhancement of CQDs’ properties. This review is primarily focused on the recent developments in carbon dots and their application in the sensing of different chemical species within the last five years. Furthermore, special emphasis has been made regarding the green approaches for obtaining CQDs and nanomaterial characterization toward better understanding the mechanisms of photoluminescent behavior and sensing performance. In addition, some of the challenges and future outlooks in CQDs research have been briefly outlined.

Natural source of carbon dots from part of a plant and its applications: a review

Carbon dots (CDs) are carbon nanoparticles with a size of less than 10 nm, and are synthesized from various sources; they have been of great interest to scientists worldwide due to their unique optical, electrical, and chemical properties. Sources of carbon are inexpensive and can be classified as a renewable natural resources. Many researchers use CDs because of their low toxicity, better water solubility, high biocompatibility, and stable photoluminescence. The simple methods for producing CDs are hydrothermal and use inexpensive equipment, have low energy consumption, simple manipulation, and one-step preparation. Since the discovery of CDs, researchers have used them in various applications such as sensing, bioimaging, drug delivery, and catalysis. In this review, CDs synthesized from natural resources such as samples from herbs, roots, leaves, flowers, and fruit and some applications are described. This review provides a summary of carbon dots that is expected to provide further information for development of new CDs.

On-off-on nanosensors of carbon quantum dots derived from coal tar pitch for the detection of Cu2+, Fe3+, and L-ascorbic acid

Novel nitrogen-doped carbon quantum dots (N-CQDs) were synthesized by a chemical oxidation method using medium-low temperature coal tar pitch as the raw material. Such quantum dots were developed as a highly sensitive fluorescent "on-off-on" switch sensor for the selective and simultaneous sensing of Cu²⁺ and Fe³⁺. The as-prepared N-CQDs, which emit blue light, were characterized by TEM images, FT-IR spectra, Raman spectroscopy, XPS analysis, fluorescence spectra, and UV-vis absorption spectra. The results showed that the N-CQDs exhibit outstanding optical properties and high optical stability within the pH range of 4-10, with a quantum yield of approximately 7%. Additionally, the material performed as an "on-off" sensor which can be dramatically extinguished by Cu²⁺ and Fe³⁺. A linear relationship between Cu²⁺ and Fe³⁺ ion concentration and fluorescence intensity was observed in the range from 0 to 50 μM. The limits of detection of the fluorescent sensor toward Cu²⁺ and Fe³⁺ were 0.16 μM and 0.173 μM, respectively. The Fe³⁺-quenched N-CQDs were restored after adding L-ascorbic acid, due to the redox reaction between Fe³⁺ and L-ascorbic acid, which resulted in the detachment of Fe³⁺ from the surface of the N-CQDs. The linear range for the detection of L-ascorbic acid was 0-28 μM. Therefore, the amount of L-ascorbic acid can be measured by using the sensing system consisting of Fe³⁺ and N-CQDs. In consequence, N-CQDs are considered an important material for the detection of Cu²⁺ and Fe³⁺ in water samples or L-ascorbic acid in drugs.

A review on analytical methods with special reference to electroanalytical methods for the determination of some anticancer drugs in pharmaceutical and biological samples

It is widely accepted that cancer, the second leading cause of death, is a morbidity with big impacts on the global health. In the last few years, chemo-therapeutic treatment continually induces alone most lengthy consequents, which is extremely harmful for the physiological and psychological health of the patients. In the present research, we discuss the recent techniques for employed for extraction, and quantitative determination of such compounds in pharmaceutical, and biological specimens. In the frame of this information, this review aims to provide basic principles of chromatography, spectroscopy, and electroanalytical methods for the analysis of anticancer drugs published in the last three years. The review also describes the recent developments regarding enhancing the limit of detection (LOD), the linear dynamic range, and so forth. The results show that the LOD for the chromatographic techniques with the UV detector was obtained equaled over the range 2.0 ng mL^-1-0.2 μg mL^-1, whereas the LOD values for analysis by chromatographic technique with the mass spectrometry (MS) detector was found between 10.0 pg mL^-1-0.002 μg mL^-1. The biological fluids could be directly injected to capillary electrophoresis (CE) in cases where the medicine concentration is at the contents greater than mg L^-1 or g L^-1. Additionally, electrochemical detection of the anticancer drugs has been mainly conducted by the voltammetry techniques with diverse modified electrodes, and lower LODs were estimated between 3.0 ng mL^-1-0.3 μg mL^-1. It is safe to say that the analyses of anticancer drugs can be achieved by employing a plethora of techniques such as electroanalytical, spectroscopy, and chromatography techniques.

Fluorescence quenching mechanism and the application of green carbon nanodots in the detection of heavy metal ions: a review

This review article highlights the quenching mechanism and applications of green CNDs for the detection of metal ions.

Sensor and Bioimaging Studies Based on Carbon Quantum Dots: The Green Chemistry Approach

Since carbon quantum dots have high photoluminescent efficiency, it has been a desired material in sensor and bioimaging applications. In recent years, the green chemistry approach has been preferred and the production of quantum dots has been reported in many studies using different precursors from natural, abundant, or waste sources. Hydrothermal, chemical oxidation, microwave supported, ultrasonic, solvothermal, pyrolysis, laser etching, solid-state, plasma, and electrochemical methods have been reported in the literature. In this review article, green chemistry strategies for carbon quantum dot synthesis is summarized and compared with conventional methods using methodologic and statistical data. Furthermore, a detailed discussion on sensor and bioimaging applications of carbon quantum dots produced with green synthesis approaches are presented with a special focus on the last decade.

Plant Part-Derived Carbon Dots for Biosensing

Carbon dots (CDs) are a new cluster of carbon atoms with particle size less than 10 nm. CDs also exhibit interesting fluorescence (FL) properties. CDs are attractive because of their fascinating characteristics including low toxicity, good water solubility, and tremendous biocompatibility. Recently, CDs have been investigated as biosensors for numerous target analytes. Meanwhile, the utilization of cheap and renewable natural resources not only fulfills the pressing requirement for the large-scale synthesis of CDs but also encourages the establishment of sustainable applications. The preparation of CDs using natural resources, i.e., plants, offers several advantages as it is inexpensive, eco-friendly, and highly available in the surroundings. Plant parts are readily available natural resources as the starting materials to produce CDs with different characteristics and attractive applications. Several review articles are now available covering the synthesis, properties, and applications of CDs. However, there is no specific and focused review literature discussing plant part-derived CDs for biosensing applications. To handle this gap, we provide a review of the progress of CDs derived from various plant parts with their synthesis methods, optical properties, and biosensing applications in the last five years. We highlight the synthesis methods and then give an overview of their optical properties and applications as biosensors for various biomolecules and molecules in biological samples. Finally, we discuss some future perspectives for plant part-derived CDs for better material development and applications.

A review of carbon quantum dots and their applications in wastewater treatment

Carbon quantum dots (CQDs) are a fascinating class of carbon nanoparticles with sizes around 10 nm. The unique properties of CQDs are low toxicity, chemical inertness, excellent biocompatibility, photo-induced electron transfer and highly tunable photoluminescence behaviour. Sustainable raw materials are commonly used for the fabrication of CQDs because they are cost-effective, eco-friendly and effective to minimise waste production. CQDs can be fabricated using laser ablation, microwave irradiation, hydrothermal reaction, electrochemical oxidation, reflux method and ultrasonication. These methods undergo several chemical reactions such as oxidation, carbonisation, pyrolysis and polymerisation processes to produce CQDs. Due to small particle sizes of CQDs, they possess strong tunable fluorescent properties and highly photo-luminescent emissions. It also contains oxygen-based functional groups and highly desired properties as semiconductor nanoparticles. Therefore, CQDs are promising nanomaterials for photo-catalysis, ions sensing, biological imaging, heavy metal detection, adsorption treatment, supercapacitor, membrane fabrication and water pollution treatment. This review paper will discuss the physical and chemical properties of CQDs, raw materials and methods used in the fabrication of CQDs, the stability of CQDs as well as their potential applications in wastewater treatment and biomedical field.