A "Turn-On" thiol functionalized fluorescent carbon quantum dot based chemosensory system for arsenite detection

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Arsenic field test kits based on solid-phase fluorescence filter effect induced by silver nanoparticle formation

Millions of people worldwide are affected by naturally occurring arsenic in groundwater. The development of a low-cost, highly sensitive, portable assay for rapid field detection of arsenic in water is important to identify areas for safe wells and to help prioritize testing. Herein, a novel paper-based fluorescence assay was developed for the on-site analysis of arsenic, which was constructed by the solid-phase fluorescence filter effect (SPFFE) of AsH3-induced the generation of silver nanoparticles (AgNPs) toward carbon dots. The proposed SPFFE-based assay achieves a low arsenic detection limit of 0.36 μg/L due to the efficient reduction of Ag+ by AsH3 and the high molar extinction coefficient of AgNPs. In conjunction with a smartphone and an integrated sample processing and sensing platform, field-sensitive detection of arsenic could be achieved. The accuracy of the portable assay was validated by successfully analyzing surface and groundwater samples, with no significant difference from the results obtained through mass spectrometry. Compared to other methods for arsenic analysis, this developed system offers excellent sensitivity, portability, and low cost. It holds promising potential for on-site analysis of arsenic in groundwater to identify safe well locations and quickly obtain output from the global map of groundwater arsenic.

Alendronate-Functionalized Graphene Quantum Dots as an Effective Fluorescent Sensing Platform for Arsenic Ion Detection

Alendronate-functionalized graphene quantum dots (ALEN-GQDs) with a quantum yield of 57% were synthesized via a two-step route: preparation of graphene quantum dots (GQDs) by pyrolysis method using citric acid as the carbon source and post functionalization of GQDs via a hydrothermal method with alendronate sodium. After careful characterization of the obtained ALEN-GQDs, they were successfully employed as sensing materials with superior selectivity and sensitivity for the detection of nanomolar levels of arsenic ions (As(III)). According to the mechanistic investigation, arsenic ions can quench the fluorescence intensity of ALEN-GQDs through metal-ligand interaction between the As(III) ions and the surface functional groups of the fluorescent probe. This probe provided a rapid method to monitor As(III) with a wide detection range (44 nM-1.30 µM) and a low detection limit of 13 nM. Finally, to validate the applicability, this novel fluorescent probe was successfully applied for the quantitative determination of As(III) in rice and water samples.

Carbon Dots-Embedded Silica Tubes: An Excitation-Independent Yellow-Emitting Turn-On Probe for Simultaneous Detection and Removal of Inorganic Arsenic with In Vivo Tracking in Living Organisms

The environmental monitoring and remediation of highly toxic inorganic arsenic species in natural water are needed for the benefit of the ecosystem. Current studies on arsenic detection and removal often employ separate materials, which exhibit blue luminescence with fluorescence quenching, making them unsuitable for biological and environmental samples. In this study, carbon dot-embedded mesoporous silica tubes functionalized with melamine are synthesized to address these limitations and enable specific and turn-on probing of inorganic arsenic. The newly synthesized material demonstrates excitation-independent yellow luminescence and can effectively detect both As (III) and As (V) at low detection limits (11 × 10-9 m, 11.2 × 10-9 m), well below the prescribed threshold limits in drinking water. It also exhibits a high adsorption capacity (≈125, 159 mg g-1 ) with fast kinetics. The material's applicability in environmental samples is validated through the successful quantification of arsenic in real samples with satisfactory recoveries. Moreover, the material shows recyclability for reuse, as demonstrated by its arsenic adsorption and desorption for several cycles under basic conditions. Additionally, the material's capability for monitoring arsenic in a biological sample (Artemia salina) is demonstrated through fluorescence imaging. The encouraging outcomes underscore the material's potential use in monitoring and mitigating arsenic in aqueous systems.

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

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

Design of a Synthetic Strategy to Achieve Enhanced Fluorescent Carbon Dots with Sulfur and Nitrogen Codoping and Its Multifunctional Applications

Here, a rational strategy to achieve multifunctional N, S codoped carbon dots (N, S-CDs) is reported, aiming to improve the photoluminescence quantum yields (PLQYs) of the CDs. The synthesized N, S-CDs have excellent stability and emission properties independent of excitation wavelength. Through the introduction of S element doping, the fluorescence emission of CDs is red-shifted from 430 to 545 nm, and the corresponding PLQYs can be greatly enhanced from 11.2% to 65.1%. It is found that the doping of S elements causes an increase in the size of CDs and an elevated graphite N content, which may be the key factors to cause the redshift of fluorescence emission. Furthermore, the introduction of S element also serves to suppress the nonradiative transitions, which may be responsible for the elevated PLQYs. Besides, the synthesized N, S-CDs have certain solvent effect and can be applied to detect water content in organic solvents, and have strong sensitivity to alkaline environment. More importantly, the N, S-CDs can be used to achieve an "on-off-on" dual detection mode between Zr4+ and NO2 - . In addition, N, S-CDs combinedwith polyvinylpyrrolidone (PVP) can also be utilized as fluorescent inks for anti-counterfeiting applications.

Nanomaterials-based biosensor and their applications: A review

A sensor can be called ideal or perfect if it is enriched with certain characteristics viz., superior detections range, high sensitivity, selectivity, resolution, reproducibility, repeatability, and response time with good flow. Recently, biosensors made of nanoparticles (NPs) have gained very high popularity due to their excellent applications in nearly all the fields of science and technology. The use of NPs in the biosensor is usually done to fill the gap between the converter and the bioreceptor, which is at the nanoscale. Simultaneously the uses of NPs and electrochemical techniques have led to the emergence of biosensors with high sensitivity and decomposition power. This review summarizes the development of biosensors made of NPssuch as noble metal NPs and metal oxide NPs, nanowires (NWs), nanorods (NRs), carbon nanotubes (CNTs), quantum dots (QDs), and dendrimers and their recent advancement in biosensing technology with the expansion of nanotechnology.

Picomolar detection of As(III) ions by using hydrothermal synthesis of functionalized polymer dots as a highly selective fluorescence sensor

Arsenic is a toxic and ubiquitous metalloid that leads to a widespread health risk to human beings and other living organisms. In this paper, a novel water-soluble fluorescent probe based on functionalized polypyrrole dots (FPPyDots) was designed and applied to determine As(III) selectively and sensitively in aqueous media. FPPyDots probe was synthesized by using a hydrothermal method, via the facile chemical polymerization of pyrrole (Py) and cysteamine (Cys) and then functionalized with ditheritheritol (DTT). To investigate the chemical composition, morphology, and optical properties of the resultant fluorescence probe various characterization techniques including FTIR, EDC, TEM, Zeta potential, UV-vis, and fluorescence spectroscopies were used. The Stern-Volmer equation was used for calibration curves and show a negative deviation with the two linear concentration ranges of 270-2200 pM and 2.5-22.5 nM with an excellent limit of detection (LOD) of 110 pM. FPPyDots exhibit high selectivity to As(III) ions over various transition and heavy metal ions interferences. The performance of the probe has also been perused concerning the pH effect. Finally, to illustrate the applicability and reliability of the FPPyDots probe, the As(III) traces were identified in water real samples and compared with ICP-OES analysis.

Research Progress in Fluorescent Probes for Arsenic Species

Arsenic is a toxic non-metallic element that is widely found in nature. In addition, arsenic and arsenic compounds are included in the list of Group I carcinogens and toxic water pollutants. Therefore, rapid and efficient methods for detecting arsenic are necessary. In the past decade, a variety of small molecule fluorescent probes have been developed, which has been widely recognized for their rapidness, efficiency, convenience and sensitivity. With the development of new nanomaterials (AuNPs, CDs and QDs), organic molecules and biomolecules, the conventional detection of arsenic species based on fluorescence spectroscopy is gradually transforming from the laboratory to the portable kit. Therefore, in view of the current research status, this review introduces the research progress of both traditional and newly developed fluorescence spectrometry based on novel materials for arsenic detection, and discusses the potential of this technology in the rapid screening and field testing of water samples contaminated with arsenic. The review also discusses the problems that still exist in this field, as well as the expectations.

Affinity of carbon quantum dots anchored within metal organic framework matrix as enhancer of plant nourishment

Nano-fertilizers were ascribed to be significantly advantageous with minimizing the negative effects of requiring excessive contents in the soil and reducing the number of times for fertilization. Herein, the superior affinity of carbon quantum dots (CQDs) anchored within metal organic framework (Cu-BTC) matrix was investigated for the first time as a fertilizer for sunflower. CQDs were nucleated from alkali-hydrolyzed carboxymethyl cellulose (CMC) via the hydrothermal technique. The synthesized CQDs (6.8 ± 3.7 nm) were anchored within Cu-BTC (crystalline rod-like structure) matrix, to produce CQDs@Cu-BTC composite. The obtained CQDs and CQDs@Cu-BTC were applied as nutrients for the sunflower plant. The chlorophyll a and carotenoids contents were 0.465 & 0.497 and 0.350 & 0.364 mg/g after treatment with CQDs & CQDs@Cu-BTC, respectively. The shoot length of sunflower sample was increased after feeding with CQDs and CQDs@Cu-BTC to be 38.7 and 46.5 cm, respectively. The obtained results confirmed that, the synthesized CQDs@Cu-BTC showed superiority as nutrient material via enhancing the growth and physiological properties of sunflower and consequently could be used as fertilizer for plants instead of the commercial nutrient.

Carbon Dots: An Excellent Fluorescent Probe for Contaminant Sensing and Remediation

Pollution-induced degradation of the environment is a serious problem for both developing and developed countries. Existing remediation methods are restricted, necessitating the development of novel remediation technologies. Nanomaterials with unique characteristics have recently been developed for remediation. Quantum dots (QDs) are semiconductor nanoparticles (1-10 nm) with optical and electrical characteristics that differ from bigger particles owing to quantum mechanics, making them intriguing for sensing and remediation applications. Carbon dots (CDs) offer better characteristics than typical QDs, such as, CdSe QDs in terms of contaminant sensing and remediation. Non-toxicity, chemical inertness, photo-induced electron transfer, good biocompatibility, and adjustable photoluminescence behavior are all characteristics of CDs. CDs are frequently made from sustainable raw materials as they are cost-effective, environmentally compactable, and excellent in reducing waste generation. The goal of this review article is to briefly describe CDs fabrication methods, to deeply investigate the criteria and properties of CDs that make them suitable for sensing and remediation of contaminants, and also to highlight recent advances in their use in sensing and remediation of contaminants.

Using functionalized asphaltenes as effective adsorbents for the removal of chromium and lead metal ions from aqueous solution

For the first time, functionalized asphaltene has been designed, synthesized, and used for the removal of heavy metals from the water. Asphaltene was separated from the crude oil with the addition of n-alkanes. Asphaltene having a complex chemical structure including multilayered and clustered aromatic fused rings bearing aliphatic chains. Asphaltene also contains heteroatoms like N, S, and O atoms along with Ni and V as prominent trace metals. On functionalization of asphaltene with nitric acid, the aliphatic chains and some of the naphthenic rings broke down and developed -COOH, -CO, C-O, and other oxygen functional groups which are playing key roles as surface-active agents in the removal of the heavy metals via chemisorption. The study was conducted using different parameters such as dose, time, pH, and concentration. The adsorption efficiency for this material at pH 4 is excellent for the removal of chromium and lead. The Langmuir, Freundlich and Temkin adsorption isotherm models as well as Lagergren pseudo second-order kinetic model were investigated. The positive enthalpies ΔHs confirm that the adsorption process is endothermic and the negative free energies ΔGs confirm the spontaneity of the process. The good efficiency of the adsorption implies the efficacy in the removal of the heavy metal ions, as well as the good efficiency in desorption, which implies the excellent recovery of the adsorbent. The effective reusability of this adsorbent makes it applicable for industrial water treatment from contaminants.

Synthesis, Purification, and Characterization of Carbon Dots from Non-Activated and Activated Pyrolytic Carbon Black

In this work, carbon dots were created from activated and non-activated pyrolytic carbon black obtained from waste tires, which were then chemically oxidized with HNO3. The effects caused to the carbon dot properties were analyzed in detail through characterization techniques such as ion chromatography; UV-visible, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy; ζ potential; transmission electron microscopy (TEM); and spectrofluorometry. The presence of functional groups on the surface of all carbon dots was revealed by UV-visible, FTIR, XPS, and Raman spectra. The higher oxidation degrees of carbon dots from activated precursors compared to those from nonactivated precursors resulted in differences in photoluminescence (PL) properties such as bathochromic shift, lower intensity, and excitation-dependent behavior. The results demonstrate that the use of an activating agent in the recovery of pyrolytic carbon black resulted in carbon dots with different PL properties. In addition, a dialysis methodology is proposed to overcome purification obstacles, finding that 360 h were required to obtain pure carbon dots synthesized by a chemical oxidation method.

Recent Advancements in the Technologies Detecting Food Spoiling Agents

To match the current life-style, there is a huge demand and market for the processed food whose manufacturing requires multiple steps. The mounting demand increases the pressure on the producers and the regulatory bodies to provide sensitive, facile, and cost-effective methods to safeguard consumers' health. In the multistep process of food processing, there are several chances that the food-spoiling microbes or contaminants could enter the supply chain. In this contest, there is a dire necessity to comprehend, implement, and monitor the levels of contaminants by utilizing various available methods, such as single-cell droplet microfluidic system, DNA biosensor, nanobiosensor, smartphone-based biosensor, aptasensor, and DNA microarray-based methods. The current review focuses on the advancements in these methods for the detection of food-borne contaminants and pathogens.

A Chelation-enhanced Fluorescence Assay using Thiourea Capped Carbonaceous Fluorescent Nanoparticles for As (III) Detection in Water Samples

Herein, we designed a sensitive and selective "Turn-On" fluorescence nanosensor using water-soluble carbonaceous fluorescent nanomaterials (CFNs) functionalized with thiourea (CFNs-Thiourea) for efficient detection of trace concentrations of arsenic (III) in aqueous samples. The CFNs and CFNs-Thiourea were characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and fourier transformed infrared spectroscopy (FTIR). The emission peak intensity of proposed nanosensor at 425 nm was gradually enhanced on arsenite addition in a wide detection range (3.3-828.5 µg L^-1) attributed to the binding of arsenite species with sulfur groups of CFNs-Thiourea. The limit of detection (LOD) was 0.48 µg L^-1 being much lower than the World Health Organization (WHO) recommended threshold value of 10 µg L^-1. Furthermore, the as-prepared CFNs-Thiourea exhibited a superb selectivity for As (III) compared to various cations and anions, such as; NO₃^-, NO₂^-, F^-, Ni²⁺, Fe³⁺, Cu²⁺, Ca²⁺, Mg²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Pb²⁺, F^-, Cl^-, Mn²⁺, Cr³⁺, Co²⁺, Cd²⁺, Bi³⁺, Al³⁺ and As (V) at 100 folds concentration of As (III). The turn on fluorescence nanosensor was successfully exploited for quantification of arsenic in spiked water samples with acceptable efficiencies.

Fluorescein Based Fluorescence Sensors for the Selective Sensing of Various Analytes

Fluorescein molecules are extensively used to develop fluorescent probes for various analytes due to their excellent photophysical properties and the spirocyclic structure. The main structural modification of fluorescein occurs at the carboxyl group where different groups can be easily introduced to produce the spirolactam structure which is non-fluorescent. The spirolactam ring opening accounts for the fluorescence and the dual sensing of analytes using fluorescent sensors is still a topic of high interest. There is an increase in the number of dual sensors developed in the past five years and quite a good number of fluorescein derivatives were also reported based on reversible mechanisms. This review analyses environmentally and biologically important cations such as Cu2+, Hg2+, Fe3+, Pd2+, Zn2+, Cd2+, and Mg2+; anions (F-, OCl-) and small molecules (thiols, CO and H2S). Structural modifications, binding mechanisms, different strategies and a comparative study for selected cations, anions and molecules are outlined in the article.

Graphene/fluorescein dye-based sensor for detecting As(III) in drinking water

A complex of reduced graphene oxide (rGO) and fluorescein (FL) dye nanoparticles of size between 50 and 100 nm has been prepared and its sensing performance for detection of As(III) in drinking water has been reported. When As(III) binds to the rGO-FL nanoparticles the relative quenching of fluorescence was increased with increase in As(III) concentration thus provide two linear calibration ranges (0-4.0 mmol L-1 and 4.0-10 mmol L-1). The fluorescence quenching mechanism was investigated by using time-resolved fluorescence spectroscopy and molecular modeling. The detection limit of this sensor has been determined as equal to 0.96 µg L-1 which is about 10 times lower than the WHO stipulated standard for As(III) in drinking water (10 µg L-1). The analytical performance and potential application of the nanosensor was compared to commercial field kits used in arsenic monitoring. The sensor proposed in this study is fast, sensitive and accurate for detection of As(III) in drinking water and environmental samples.

Anthranilic Acid Schiff Base as a Fluorescent Probe for the Detection of Arsenite and Selenite: A Detailed Investigation of Analytical Parameters and Mechanism for Interaction

The exploration of an anthranilic acid based Schiff base SB as a "Turn-ON" fluorescent probe for the detection of highly toxic selenite (Se^IV) and arsenite (As^III) species in an aqueous medium is described. The selectivity of SB towards Se^IV and As^III in the presence of other ions was investigated by some spectrofluorimetric and ¹H NMR spectroscopic experiments. The studies revealed the interaction between SB and As^III via the deprotonation of phenolic -OH, which enhanced the conjugation in phenolate ion and in turn enhanced the emission response. The SB has analytical prospects for the quantification of As^III and Se^IV with good sensitivity (LODs; 5.15 ppb for Se^IV and 3.12 ppb for As^III calculated by S/N = 3σ/K). Furthermore, it can be used to evaluate real and synthetic samples for the presence of Se^IV and As^III species as well as the fabrication of on-spot recognition devices (in the form of silica gels SB@SiO₂ and silica coated TLC aluminium strips SB@SiO₂@Al).

Nano-Enabled sensors for detection of arsenic in water

The elevated cases of arsenic contamination reported across the globe have made its early detection and remediation an active area of research. Although, the World Health Organisation has set the maximum provisional value for arsenic in drinking water at 10 parts per billion, yet concentrations as high as 5000 parts per billion are still reported. In human beings, chronic arsenic exposure can culminate into lethal diseases such as cancer. Thus, there is a need for urgent emergence of efficient and reliable detection system. This paper offers an overview of the state-of-art knowledge on current arsenic detection mechanisms. The central agenda of this paper is to develop an understanding into the nano-enabled methods for arsenic detection with an emphasis on strategic fabrication of nanostructures and the modulation of nanomaterial chemistry in order to strengthen the knowledge into novel nano-enabled solutions for arsenic contamination. Towards the end prospects for arsenic detection in water are also prompted.

Carbon dots-MnO2 nanocomposites for As(III) detection in groundwater with high sensitivity and selectivity

As(iii) pollution has caused increasing concern due to its significant impact in environmental safety and human health. Carbon dots (CDs)-MnO2 nanocomposites were prepared and characterized for As(iii) detection. The intense blue fluorescence of CDs can be greatly quenched by functionalization with MnO2 nanosheets due to the existence of the fluorescence resonance energy transfer (FRET) effect. CDs-MnO2 nanocomposites were then used as a fluorescence sensor for As(iii) detection with high detection sensitivity and selectivity. The redox reaction between As(iii) and MnO2 nanosheets can induce the decomposition of MnO2 and termination of the FRET process. Then the blue fluorescence originating from CDs can be recovered. The detection limit of CDs-MnO2 nanocomposites toward As(iii) was calculated to be 16.8 nM (1.40 ppb) in a linear concentration range of 0-200 nM. CDs-MnO2 nanocomposites were also found to possess highly selective ability toward As(iii) detection. In addition, the spiked and recovery test also confirmed the practicality and reliability of CDs-MnO2 nanocomposites toward As(iii) detection in real water samples, such as groundwater etc. Our research has provided a reliable tool and strategy for visual detection of As(iii) with outstanding sensing ability.

Paper-based microfluidic aptasensors

For in-situ disease markers detection, point-of-care (POC) diagnosis has great advantages in speed and cost compared with traditional techniques. The rapid diagnosis, prognosis, and surveillance of diseases can significantly reduce disease-related mortality and trauma. Therefore, increasing attention has been paid to the POC diagnosis devices due to their excellent diagnosis speed and portability. Over the past ten years, paper-based microfluidic aptasensors have emerged as a class of critical POC diagnosis devices and various aptasensors have been proposed to detect various disease markers. However, most aptasensors need further improvement before they can actually enter the market and be widely used. There is thus an urgent need to sort out the key points of preparing the aptasensors and the direction that needs to be invested in. This review summarizes the representative articles in the development of paper-based microfluidic aptasensors. These works can be divided into paper-based optical aptasensors and paper-based electrochemical aptasensors according to their output signals. Significant focus is applied to these works according to the following three parts: (1) The ingenious design of device structure; (2) Application and synthesis of nanomaterial; (3) The detection principle of the proposed aptasensor. This is a detailed and comprehensive review of paper-based microfluidic aptasensors. The accomplishments and shortcomings of the current aptasensors are outlined, the development direction and the future prospective are given. It is hoped that the research in this review can provide a reference for further development of more advanced, more effective paper-based microfluidic aptasensors for POC disease markers diagnosis.

Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH 3 -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg2+ are better than to other metal ions (Ag+, Al3+, Ba2+, Cd2+, Co3+, Cu2+, Cr3+, Fe3+, Ga2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+). According to the standard curve diagram, the detection limits of CH 3 -R6G and CN-R6G were determined to be 1.34 × 10-8 and 1.56 × 10-8 M, respectively. Reaction of the probes with Hg2+ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH 3 -R6G and CN-R6G have been successfully used for imaging Hg2+ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg2+ in vivo.

Carbon Dots for Forensic Applications: A Critical Review

Owing to their superior fluorescence performance, inexpensive synthesis and nontoxic nature, carbon dots (C-dots) are systematically explored in a variety of applications; in this review, we outline and critically discuss recent trends with respect to their potential exploitation in criminal investigation, forensic toxicology and anti-counterfeit interventions. Capitalising on their colour-tuneable behaviour (in the sense that they adopt different colours with respect to the incident radiation), C-dot-based compositions are ideal for the visual enhancement of latent fingerprints, affording improved contrast against multicoloured and patterned backgrounds. As highly sensitive and highly selective optical nanoprobes, C-dots show excellent analytical performance in detecting biological compounds, drugs, explosives, heavy metals and poisonous reactants. In addition, benefiting from their versatile structural and chemical composition, C-dots can be incorporated into ink and polymeric formulations capable of functioning as a new generation of cost-effective barcodes and security nanotags for object authentication and anti-counterfeit applications. Translating these encouraging research outcomes into real-life innovations with significant social and economic impact requires an open, multidisciplinary approach and a close synergy between materials scientists, biologists, forensic investigators and digital engineers.

Copper nanoclusters @ nitrogen-doped carbon quantum dots-based ratiometric fluorescence probe for lead (II) ions detection in porphyra

A novel ratiometric fluorescence probe was proposed for detecting lead (II) ions (Pb²⁺) in porphyra, the approach was based on copper nanoclusters and nitrogen-doped carbon quantum dots (CuNCs-CNQDs). In this probe, the CuNCs delivered the response signal, the fluorescence of which was enhanced by Pb²⁺ due to the aggregation-induced emission enhancement (AIEE) between Pb²⁺ and CuNCs. The CNQDs provided the self-calibration signal, whose fluorescence remained almost unchanged in coexistence with Pb²⁺. According to the change of fluorescence intensity ratio between the fluorophores, CuNCs-CNQDs nanohybrid was used as ratiometric probes for the sensitive detection of Pb²⁺ in the range of 0.010-2.5 mg L^-1, with a detection limit of 0.0031 mg L^-1. Finally, the probe was successfully applied to detect Pb²⁺ in porphyra with relative standard deviations (RSDs) lower than 5%. This study provides a straightforward, stable, and sensitive approach for detecting Pb²⁺ in porphyra.

Atomically dispersed Eu(III) sites in natural deep eutectic solvents based fluorescent probe efficient identification of Fe3+ and Cu2+ in wastewater

Heavy metal ions in wastewater have brought serious environmental pollution. To improve the detection efficiency, it is important to find useful fluorescent probes. The emerging green natural deep eutectic solvents (NADESs) offer attractive option for "green" detection for its good biocompatibility, easy preparation, and high sensitivity. In this study, a multi-functionalized fluorescent probe with atomically dispersed EuCl₃·6H₂O in amino acid-based NADESs (l-Glutamic acid/Glycerol, l-Glu/Gly) was synthesized by metal-ligand coordination interactions with a mass ratio of 15:1. Combined with the NADESs and rare earth metal, the l-Glu/Gly/EuCl₃·6H₂O could form the amino site and Eu²⁺ site fluorescent centers. Under the excitation wavelength of 370 nm, it had dual emission peaks at 425 nm and 470 nm with efficient resonance energy transfer. The stable optoelectronic properties of l-Glu/Gly/EuCl₃·6H₂O under external factors, such as mass ratio (13,1 to 18:1), temperature (30-50 °C), pH (1 to 14) and storage time ( >42 days), approved l-Glu/Gly/EuCl₃·6H₂O an excellent fluorescence probe. In the application of water-quality monitoring, Fe³⁺ and Cu²⁺ could react with l-Glu/Gly/EuCl₃·6H₂O in different reactive patterns. The blue fluorescence was quenched by Fe³⁺ and enhanced by Cu²⁺, thus metal ions could be distinguished with high sensitivity. The detective process was determined and the fluorescent mechanism was also proposed. l-Glu/Gly/EuCl₃·6H₂O fluorescent probe was demonstrated to be an efficient fluorescent probe for metal detection avoiding the hydrothermal process, and the cumbersome of ilter, dialysis, freeze drying.

A novel and sensitive ratiometric fluorescence assay for carbendazim based on N-doped carbon quantum dots and gold nanocluster nanohybrid

A novel fluorescence "turn on" ratiometric fluorescent sensor was employed to determine carbendazim. The sensing process was achieved through the strong fluorescence resonance energy transfer (FRET) between nitrogen doped carbon quantum dots (N-CQDs) and gold nanocluster (AuNCs). The photoluminescence intensity of N-CQDs can be deactivated by AuNCs through FRET effect and recovered by the addition of carbendazim. The ratiometric detection of carbendazim is achieved by recording the photoluminescence and second-order Rayleigh scattering (SRS) signal of N-CQDs/AuNCs system. With the introduction of carbendazim to the sensing platform resulted in the photoluminescence and SRS signal of N-CQDS/AuNCs enhancing. UV-vis absorption, Zeta potential and fluorescence lifetime analyses indicate that the fluorescence turn on process can be attributed to the aggregation of AuNCs breaks the FRET process and increases SRS intensity. N-CQDs/AuNCs probe present a good sensitivity and selectivity for carbendazim detection, with two linear response ranges (1-100 μM, 150-1000 μM), low detection limit of 0.83 μM and 37.25 μM. Furthermore, real sample analyses indicate that the as-presented sensor has potentials in carbendazim determination in real sample analyses.

4-aminoantipyrine modified carbon dots and their analytical applications through response surface methodology

A sensitive and selective nanoprobe for detection of hypochlorite (OCl^-) based on 4-aminoantipyrine (AAP) modified carbon dots (CDs-AAP) has been prepared. The CDs-AAP exhibit an emission peak at 484 nm when the excitation wavelength is 370 nm, accompanying 36 nm red shift compare with the pristine CDs. The addition of OCl^- lead to the AAP on the surface of CDs experience a process of hydrazide hydrolysis and double bond addition, causing the singlet and triplet electrons of the excited state more closer in energy (ie, the energy difference between the two is reduced), eventually quenching the fluorescence of CDs due to heavy atomic effects. Central composite design (CCD) and response surface method (RSM) were used to optimize the detection variables of pH, incubation time and temperature. The designed model study indicated that the optimum detection conditions was pH 7.0, temperature 30 °C and incubation time 20 min, respectively. Under optimal conditions, the fluorescent intensity of the nanoprobe linearly responded to the OCl^- concentration from 3 μM to 36 μM and the limit of detection was 40 nM. The proposed nanoprobe was successfully used to the detection of OCl^- in tap water and pool water, and the recovery were in the range of 94% - 103%. In addition, the nanoprobe was also applied in imaging of VMSCs cells and labeling E.coli.

A new CQDs/f-MWCNTs/GO nanocomposite electrode for arsenic (10−12M) quantification in bore-well water and industrial effluents

Strategic combination ofCQDs/f-MWCNTs/GO/GCE for pico-molar arsenic sensing.

Green synthesis, biomedical and biotechnological applications of carbon and graphene quantum dots. A review

Carbon and graphene quantum dots are prepared using top-down and bottom-up methods. Sustainable synthesis of quantum dots has several advantages such as the use of low-cost and non-toxic raw materials, simple operations, expeditious reactions, renewable resources and straightforward post-processing steps. These nanomaterials are promising for clinical and biomedical sciences, especially in bioimaging, diagnosis, bioanalytical assays and biosensors. Here we review green methods for the fabrication of quantum dots, and biomedical and biotechnological applications.

Development of ultrasensitive and As(iii)-selective upconverting (NaYF4:Yb3+,Er3+) platform

Solid-phase, LRET-based NaYF₄:Yb³⁺,Er³⁺ platform for the ultrasensitive (1 nM) detection of arsenic.

Nanomaterial-based aptamer sensors for arsenic detection

Arsenic (As) is a highly toxic contaminant in the environment and a serious carcinogen for the human being. The toxicity of arsenic significantly threatens environmental and human health. The effective removing technology for arsenic remains challenging, and one of the reasons is due to the lack of powerful detection method in the complex environmental matrix. There is thus an urgent need to develop novel analytical methods for arsenic, preferably with the potential for the field-testing. To combat arsenic pollution and maintain a healthy environment and eco-system, many analytical methods have been developed for arsenic detection in various samples. Among these strategies, biosensors hold great promise for rapid detection of arsenic, in particular, nanomaterials-based aptamer sensors have attracted significant attention due to their simplicity, high sensitivity and rapidness. In this paper, we reviewed the recent development and applications of aptamer sensors (aptasensors) based-on nanomaterial for arsenic detection, in particular with emphasis on the works using optical and electrochemical technologies. We also discussed the recent novel technology in aptasensors development for arsenic detection, including nucleic acid amplification for signal enhancement and device integration for the portability of arsenic sensors. We are hoping this review could inspire further researches in developing novel nanotechnologies based aptasensors for possible on-site detection of arsenic.

A convenient and universal platform for sensing environmental nitro-aromatic explosives based on amphiphilic carbon dots

2,4,6-trinitrophenol (TNP) is environmentally deleterious substance that has been of pressing societal concern. Therefore, developing a convenient and reliable platforms for its fast and efficient detection is of paramount importance from security point of view. Herein, amphiphilic fluorescent carbon dots (CDs) were prepared by a simple solvothermal method. CDs exhibit high selectivity and sensitivity on TNP in the polar and apolar solvent and even natural water samples. Moreover, the simple and portable indicator paper can be prepared conveniently and used for sensing TNP visually with high sensitivity and fast response. Research findings obtained from this study would assist in the development of portable devices for the on-site and real-time detection of environmental hazards.

Review of Carbon and Graphene Quantum Dots for Sensing

Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluorescent, photoluminescent, chemiluminescent, and electrochemiluminescent properties are what gives them potential in sensing. In this Review, we summarize the basic knowledge on CQDs and GQDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into CQDs- and GQD-based nanomaterials in sensing. With regard to the latter, the authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilize the virtues of these nanomaterials to give us new or better sensors that could not be achieved in other ways.

New carbon dots based on glycerol and urea and its application in the determination of tetracycline in urine samples

The current study proposes a fast one-pot microwave assisted synthesis of new carbon dots (CDs) based on glycerol and urea. The novel carbon nanoparticles (GUCDs) have been appropriately characterized and exhibited good luminescent properties with a quantum yield of about 9.8%. Interestingly, the GUCDs are able to selectively interact with tetracycline class antibiotics, which produce a decrease in the native fluorescence of the CDs. On the base of these features, a new analytical method has been developed for the determination of tetracycline. The proposed method has shown satisfactory analytical parameters, such as good linearity range -between 0.5 and 25 μM (R² = 0.999₇)- and an acceptable detection limit (165 nM). Moreover, the new method has been successfully applied for tetracycline determination in urine samples with good recoveries (94.7-103%) and precision (4.6 RSD%).

Highly stable and selective measurement of Fe3+ ions under environmentally relevant conditions via an excitation-based multiwavelength method using N, S-doped carbon dots

Fast and accurate detection of Fe³⁺ under relevant natural conditions is important in environmental monitoring. In this study, an improved and simplified fluorescence method based on the multiwavelength luminescence in the visible region and the avoidance of the self-quenching property of N, S-doped carbon dots (NSC-Dots) was developed for the first time to determine Fe³⁺ concentration under varied environmental conditions. This method can simultaneously save time and provide accurate information. The as-prepared NSC-Dots exhibit two stable excitation peaks from 200 nm to 450 nm at a fixed emission wavelength (λ_em = 450 nm). A standard equation (R² = 0.995) can be derived by measuring the quenching degree of the two peaks and referring to Stern-Volmer theory. Thus, Fe³⁺ concentration was accurately determined. The interference of the environmentally relevant concentrations of other metal ions, humic acid, and pH on Fe³⁺ measurement was tested. Results showed that the standard equation can be used to accurately determine Fe³⁺ concentration within the range of the 95% prediction band. The fast and facile multiwavelength method may facilitate the real-time monitoring of Fe³⁺ concentration in complex water environments.

Bio-inspired ultrasensitive colorimetric detection of methyl isothiocyanate on nylon-6 nanofibrous membrane: A comparison of biological thiol reactivities

Living organisms, including human beings, rapidly show skin color changes after chemical poisonings, a result of toxicological or detoxification reactions caused by biological thiol compounds. On the other side, quick and portable detection of highly-volatile toxicants is an urgent need for improving human safety and personal protection, especially real-time monitoring of fumigants at low level for protection of farm workers and residents from overexposure of fumigants, vaporous pesticides. Here, we designed a rapid and portable detection method for methyl isothiocyanate (MITC) vapor by mimicking detoxification reactions of biological thiols in human bodies with MITC. The detection reaction was implemented on a nylon-6 nanofibrous membrane with ultrahigh surface areas to show color signals with the addition of Ellman's reagent. The reactivities of glutathione, N-acetyl-L-cysteine, L-homocysteine, cysteamine, and thioglycolic acid toward MITC were experimentally explored and theoretically discussed. The detection sensitivity is tunable in different biological thiol systems, which broadens the sensor applications in detection of trace amount of MITC in ambient environment and improves the protection of human safety. The new sensor system reduced the sensor operation time to 15 min and achieved the detection limit of 99 ppb, much lower than its permissible exposure limit (220 ppb).

CdSe/ZnS quantum dots coated with carboxy-PEG and modified with the terbium(III) complex of guanosine 5'-monophosphate as a fluorescent nanoprobe for ratiometric determination of arsenate via its inhibition of acid phosphatase activity

A ratiometric fluorometric method is described for the determination of arsenate via its inhibitory effect on the activity of the enzyme acid phosphatase. A nanoprobe was designed that consists of CdSe/ZnS quantum dots (QDs) coated with the terbium(III) complex of guanosine monophosphate (Tb-GMP). The nanoprobe was synthesized from carboxylated QDs, Tb(III) and GMP via binding of Tb(III) by both the carboxy and the phosphate groups. The nanoprobe, under single-wavelength excitation (at 280 nm), displays dual (red and green) emission, with peaks at around 652 nm from the QDs, and at 547 nm from the Tb-GMP coordination polymers. It is shown to be a viable nanoprobe for fluorometric determination of As(V) detection through it inhibitory action on the activity of acid phosphatase (ACP). The enzyme destroys the Tb-GMP structure via hydrolysis of GMP, and hence the fluorescence of the Tb-GMP complex is quenched. In contrast, the fluorescence of the CdSe/ZnS QDs remains inert to ACP. It therefore can serve as an internal reference signal. In the presence of arsenate (an analog of phosphate), the activity of ACP is inhibited due to competitive binding. Thus, hydrolysis of GMP is prevented. These findings were used to design a ratiometric fluorometric method for the quantification of As(V). The ratio of fluorescences at 547 and 652 nm increases linearly in the 0.5 to 200 ppb As(V) concentation range, and the limit of detection is 0.39 ppb. Under a UV lamp, the probe shows distinguishable color from green to red on increasing the concentration of As(V). Graphical abstract Schematic illustration of CdSe/ZnS quantum dot coated with carboxy-PEG and modified with the terbium(III)-GMP complex as a fluorescent nanoprobe for ratiometric determination of arsenate via its inhibition of ACP activity.

Label-free gold nanorod-based plasmonic sensing of arsenic(iii) in contaminated water

An efficient label-free strategy for arsenic(iii) sensing in water through the suppression of iron(iii)-catalyzed oxidative shortening of gold nanorods.

Hydrothermal synthesis of N-doped carbon dots from an ethanolamine–ionic liquid gel to construct label-free multifunctional fluorescent probes for Hg2+, Cu2+ and S2O32−

N-Doped carbon dots were synthesized and used to construct multifunctional fluorescent probes for Hg²⁺, Cu²⁺ and S₂O₃²⁻.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

Biomass-derived nitrogen-doped carbon quantum dots: highly selective fluorescent probe for detecting Fe3+ ions and tetracyclines

Nitrogen-doped carbon quantum dots (N-CQDs) were successfully synthesized using rice residue and glycine as carbon and nitrogen sources by one-step hydrothermal method. High quantum yield (23.48%) originated from the effective combination of nitrogen with various functional groups (CO, NH, CN, COOH and COC). The N-CQDs showed a fluorescence with the wavelength varied from 420 to 500 nm and the maximum emission wavelength being at 440 nm. N-CQDs have been importantly applied as probe to detect Fe³⁺ and tetracycline (TCs) antibiotics with remarkable performance. Using the linear relationship between fluorescence intensity and Fe³⁺ concentration, the N-CQDs could be employed as a simple, efficient sensor for ultrasensitive Fe³⁺ detection ranging from 3.32 to 32.26 µM, with a limit of detection (LOD) of 0.7462 µM. The N-CQDs showed the applicability to detect TCs. The detection limits of tetracycline, terramycin and chlortetracycline were 0.2367, 0.3739 and 0.2791 µM, respectively. The results of TC by fluorescence method in real water samples were in good agreement with standard Ultraviolet-visible (UV-vis) method. The N-CQDs have various potential applications including sensitive and selective detection of Fe³⁺ and TCs, and cellular imaging with low cytotoxicity, good biocompatibility and high permeability.