Fluorometric and electrochemical dual-mode detection of toxic flavonoid rutin based on new nitrogen and sulfur co-doped carbon dots: Enhanced selectivity based on masking the interfering flavonoids with BSA complexation

Novel fluorescence-based and portable detection platforms using nitrogen-doped carbon dots for environmental monitoring of dichloran fungicide

A novel fluorescence sensor utilizing label-free nitrogen self-doped carbon dots (NCDs) was developed for the sensitive, selective, and rapid determination of dichloran fungicide, popularly used in agricultural and horticultural fields. The NCDs were prepared from maleic anhydride and diethylenetriamine via a one-step pyrolysis process. They demonstrated strong blue fluorescence emission with a quantum yield of 12 %. With the addition of dichloran, the fluorescence emission of NCDs was quenched, attributed to the inner filter effect and dynamic quenching. They demonstrated outstanding sensitivity to dichloran with a linear range between 1.0 and 50.0 µM and a remarkably low detection limit of 7.6 nM, the best reported date. The sensing process could be repeatedly and rapidly generated within 30 s. Additionally, the NCDs exhibited selectivity towards dichloran amidst interferences, including common metal ions, organic chemicals, and other fungicides. The detection of dichloran in carrots, grapes, and drinking water was successfully accomplished using NCDs, yielding satisfactory recovery results ranging between 95.1 and 108.7 %. Moreover, a paper-based sensor based on NCDs as sensing probes was demonstrated to observe the fluorescence quenching towards dichloran, with a detection limit of 4.24 µM. It also showed high efficacy in distinguishing and selectively detecting dichloran against interferences. Therefore, this work contributes to the development of efficient and portable detection platforms with applications in environmental monitoring and agricultural fields.

Uric acid detection via dual-mode mechanism with copper-coordinated nitrogen-doped carbon dots as peroxidase mimics

Monitoring disease-related biomarkers, such as uric acid in human body fluids, is essential for effective disease management and clinical diagnosis. In this study, copper-coordinated nitrogen-doped carbon dots (Cu@N-CDs) were synthesized via a simple hydrothermal method, achieving a remarkable photoluminescence quantum yield of 44.69%. The Cu@N-CDs emitted fluorescence at 460 nm upon excitation at 360 nm, making them highly suitable for sensitive biosensing applications. For uric acid detection, a Cu@N-CDs-based probe was developed and coupled with phenol (ph-OH) and 4-aminoantipyrine (AP-NH2). In the presence of hydrogen peroxide (H2O2), generated through the enzymatic breakdown of uric acid by uricase, ph-OH and AP-NH2 reacted to form a pink-colored compound. This compound quenched the fluorescence emission of Cu@N-CDs via an inner-filter effect, enabling fluorometric detection. Additionally, for colorimetric detection, the pink compound was quantified by measuring absorbance at 510 nm. The detection strategy utilized the peroxidase-mimetic activity of Cu@N-CDs, which was further enhanced by the presence of Cu. Under optimized conditions, the fluorometric method demonstrated a linear detection range of 0.01-700 μM, while the colorimetric method showed a range of 0.07-700 μM for uric acid. The developed approach proved highly effective in detecting uric acid in human blood serum and urine samples, yielding accurate results with acceptable recovery rates. This dual-mode detection method offers a reliable, sensitive, and cost-effective tool for monitoring uric acid levels, marking a significant advancement in clinical diagnostics and personalized healthcare.

Fabrication of hybrid nanocomposites for electrochemical evaluation of food-based preservative and bioactive targets of hydrogen peroxide and rutin in real fruit and drug samples

Development of a reliable tool to detect hydrogen peroxide (H2O2) and rutin in food-derived products and bioactive flavonoids is essential for food safety. Nevertheless, food/drug-based real samples are complex matrices that affect the sensor's specificity and sensitivity. For this purpose, we developed a simple electrochemical detection platform using covalent organic framework‑silver nanoparticles (COF-AgNPs). Based on spectral and electrochemical tests, COF-AgNPs displayed enhanced electroactive sites and facile electron transfer. For H2O2 and rutin, the designed sensor surface exhibited outstanding concentration linearity of 0.5 nM-1000 μM and 1 nM-900 μM, respectively, along with superior detection limits of 0.126 nM and 0.133 nM. Additionally, it demonstrated acceptable reproducibility and interference capability. In practical analysis, H2O2 and rutin were detected in milk, fruits, and drug samples with high recovery rates of 94.60-99.31 % (n = 3). Consequently, the designed sensor is ideal for screening targets for H2O2 and rutin in food sources and for food research.

Developing a switch "OFF-ON" fluorescent probe for detection of melamine based on doubly-protected red emissive copper nanoclusters mediated by Hg2+ ions

Melamine, often used as an adulterant in infants' formula due to its high protein content, can be harmful when ingested in large amounts, leading to the formation of cyanurate-melamine co-crystals in infants and potentially causing kidney damage. In this study, we introduce a fluorescent method for the selective and reliable detection of melamine in milk and infants' formula. The fluorescent probe comprises copper nanoclusters (Cu NCs) functionalized with thiosalicylic acid (TSA) and polyvinylpyrrolidone (PVP) as double-protecting ligands. Upon the addition of Hg2+, the fluorescence emission of TSA-PVP@Cu NCs is diminished due to static quenching. Subsequently, the fluorescence emission of the TSA-PVP@Cu NCs + Hg2+ probe is restored upon the introduction of melamine, facilitated by the coordination interaction between melamine and Hg2+ and the formation of a stable chelate between them. Under optimized conditions, the fluorescence emission was recorded initially for the TSA-PVP@Cu NCs + Hg2+ probe (F°) and after melamine addition (F). The (F/F°) ratio increased with rising melamine concentrations within the range of 0.025-65 µM. The detection limit, calculated using a signal-to-noise ratio of 3, was determined to be 8.0 nM. The TSA-PVP@Cu NCs + Hg2+ probe was successfully employed to detect melamine in milk and infants' formula, yielding acceptable recovery percentages and relative standard deviations. These results underscore the reliability and efficacy of the proposed probe for the fluorometric detection of melamine in real-world samples.

Fabrication of Highly Fluorescent Nitrogen and Phosphorus Dual-Doped Carbon Dots for Selective Sensing of Rutin

Based on nitrogen and phosphorus co-doped carbon dots (NP-CDs), a direct, quick, and selective sensing probe for fluorometric detection of rutin has been developed. Utilizing ethylene diamine tetra acetic acid (EDTA) as a carbon and nitrogen source and diammonium hydrogen phosphate (NH4)2HPO4 as a nitrogen and phosphorus source. The NP-CDs were synthesized in less than 3 min with a straightforward one-step microwave pyrolysis process with a high quantum yield (63.8%). After being excited at λ = 360 nm, the produced NP-CDs displayed a maximum bluish fluorescence at λem of 420 nm. Rutin quenched the fluorescence of the produced NP-CDs based on the inner filter effect and static quenching processes. Along with the International Council of Harmonization (ICH) requirements, the developed spectrofluorometric method was validated. The linearity range was 0.50-35.00 μg/mL of rutin. The developed NP-CDs were successfully employed to determine rutin concentrations in marketed tablets. The developed method is quick, simple, consistent, sensitive, and selective, and it does not require expensive chemicals or specialized instruments. This study paves the path for future application of NP-CD in pharmaceutical analysis.

Development of silver-doped carbon dots sensor derived from lignin for dual-mode fluorometric and spectrophotometric determination of valsartan in a bulk powder and a commercial product

Doping of carbon dots (CDs) with heteroatoms has garnered growing attention in recent years as a useful method of controlling their physicochemical properties. In this study, a new dual-mode sensor based on silver-doped CDs (AgCDs) derived from lignin was developed for fluorometric and spectrophotometric determination of valsartan (VAL). The analysis of AgCDs revealed a structure that closely resembled graphene oxide, with the successful doping of Ag. The mean particle size of AgCDs was 3.50 ± 0.89 nm and it exhibited a reasonable fluorescence quantum yield of 28.1 %. The emission at 612 nm of AgCDs is quenched by VAL after being excited at 275 nm due to a combination of dynamic and static quenching mechanisms. The enhancement in the absorbance of AgCDs upon the addition of the medication was measured at 275 nm. The most favorable circumstances for the dual-mode sensing were achieved with a pH of 8 and a volume of 0.10 mL of AgCDs. The measurements were conducted using fluorometry after 3 min at 10 °C, followed by spectrophotometry after 7 min at 20 °C. The fluorometric data indicated a linear response within the range of 2.0-50.0 μg/mL, while the spectrophotometric results showed a dynamic range of 5.0-100.0 μg/mL. The limits of detection (LODs) were 0.57 and 1.38 μg/mL for the fluorometric and spectrophotometric methods, respectively. The limits of quantification (LOQs) were 1.72 and 4.19 μg/mL for the fluorometric and spectrophotometric methods, respectively. The nano sensor efficiently assessed the presence of VAL in pharmaceutical tablets and produced a favorable outcome with the mean of recovery of 98.91 % and 99.76 % with relative standard deviation (RSD%) of 0.79 and 0.78 for the fluorometric and spectrophotometric methods, respectively.

A ratiometric fluorescence nanosensor for glutathione detection based on spatially confined dual-emission of α-lipoic acid-modified gold nanoclusters and silicon nanoparticles

The development of dual-emission ratiometric fluorescent probes with aggregation-induced emission enhancement (AIEE) overcomes the limitations of gold nanocluster (Au NC)-based probes, particularly their weak intrinsic fluorescence, in real-world applications. These AIEE probes also exhibit superior detection limits and enhanced sensitivity. A novel combination for the reliable fluorometric detection of glutathione (GSH) was proposed, utilizing aggregation-induced emission enhancement (AIEE) facilitated by electrostatic interaction and spatial confinement. The probe consists of a ratiometric combination of negatively charged α-lipoic acid-modified Au NCs (LA@Au NCs) and positively charged silicon nanoparticles (SiNPs). The addition of SiNPs causes aggregation of LA@Au NCs, enhancing the fluorescence of LA@Au NCs through the AIE effect under electrostatic interaction and spatial confinement. The addition of Cu2+ quenched the emission of LA@Au NCs as a result of charge transfer. The fluorescence emissions of LA@Au NCs were restored upon the addition of GSH due to the interaction between GSH and Cu2+. Simultaneously, the emission signal of SiNPs remains unchanged, serving as an internal reference signal during GSH measurement. It was found that the fluorescence ratio (F680/F465) is directly proportional to the concentration of GSH in the range of 0.05-100 μM, with a detection limit of 1.7 nM (S/N = 3). The proposed system was applied to detect GSH in real samples, including dietary supplements, human serum, and saliva samples. This work opens new avenues for constructing novel sensors based on AIEE for detecting biomolecules.

Biosensor Based on ZIF-67-HRP and MWCNTs Nanocomposite Modified Glass Carbon Electrode for the Detection of Luteolin in Vegetables

Luteolin has various pharmacological properties, including anti-inflammatory, antioxidant, and antitumor characteristics. Due to its potential value in drugs and functional foods, it is important to develop an efficient method for detecting luteolin. In this work, the poor selectivity of existing luteolin nonenzymatic sensors was solved by translating the enzyme-catalyzed reaction from bulk solution to the surface of a horseradish peroxidase (HRP) modified electrode through an electrocatalytic oxidation process. Here, we modified the surface of a glassy carbon electrode (GCE) with metal-organic frameworks (MOFs; ZIF-67 here, abbreviated as ZIF), functional nanomaterials, and HRP and finally covered it with Nafion (NF). In this case, luteolin acts as a hydrogen donor, and the electrode acts as a hydrogen acceptor; the oxidation reaction occurs on the electrode surface. The use of ZIF-67 ensured the conformational stability of HRP to ensure the selectivity and anti-interference property, and SDS-dispersed multiwalled carbon nanotubes (MWCNTs) enhanced the electrode conductivity. The use of NF avoids shedding of the electrode material during the testing process. A UV-vis spectrophotometer was used to study the selectivity of luteolin by HRP and the compatibility between HRP and ZIF. The materials were characterized and analyzed by scanning electron microscopy and transmission electron microscopy. Due to the synergistic effect of these nanomaterials, the linear range of NF/ZIF-HRP/MWCNTs-SDS/GCE was 1.0 × 10-2 to 6.0 μM, with detection limits of 25.3 nM (S/N = 3). The biosensor showed long-term stability and reproducibility, with a relative standard deviation of 4.2% for the peak current (n = 5). Finally, the biosensor was successfully used to detect luteolin in carrots, celery, and cauliflower.

Highly Sensitive and Selective Fluorescence and Smartphone-Based Sensor for Detection of Rutin Using Boron Nitrogen Co-doped Graphene Quantum Dots

This research explores the fluorescence properties and photostability of boron nitrogen co-doped graphene quantum dots (BN-GQDs), evaluating their effectiveness as sensors for rutin (RU). BN-GQDs are biocompatible and exhibit notable absorbance and fluorescence characteristics, making them suitable for sensing applications. The study utilized various analytical techniques to investigate the chemical composition, structure, morphology, optical attributes, elemental composition, and particle size of BN-GQDs. Techniques included X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The average particle size of the BN-GQDs was determined to be approximately 3.5 ± 0.3 nm. A clear correlation between the emission intensity ratio and RU concentration was identified across the range of 0.42 to 4.1 μM, featuring an impressively low detection limit (LOD) of 1.23 nM. The application of BN-GQDs as fluorescent probes has facilitated the development of a highly sensitive and selective RU detection method based on Förster resonance energy transfer (FRET) principles. This technique leverages emission at 465 nm. Density Functional Theory (DFT) analyses confirm that FRET is the primary mechanism behind fluorescence quenching, as indicated by the energy levels of the lowest unoccupied molecular orbitals (LUMOs) of BN-GQDs and RU. The method's effectiveness has been validated by measuring RU concentrations in human serum samples, showing a recovery range between 97.8% and 103.31%. Additionally, a smartphone-based detection method utilizing BN-GQDs has been successfully implemented, achieving a detection limit (LOD) of 49 nM.

A reliable and selective ratiometric sensing probe for fluorometric determination of P2O74- based on AIE of GSH@CuNCs-assisted by Al-N@CQDs

In this study, a novel composite material was developed for the ratiometric detection of pyrophosphate anion (P2O74-). This composite consisted of Al and nitrogen co-doped carbon dots (Al-N@CQDs) and glutathione-capped copper nanoclusters (GSH@CuNCs). The Al-N@CQDs component, with its high reserved coordination capacity of Al3+, induced the non-luminescent behavior of GSH@CuNCs, resulting in an aggregation-induced emission (AIE) effect. The hybrid material (Al-N@CQDs/GSH@CuNCs) exhibited dual-emission signals at 620 nm and 450 nm after integrating the two independent materials utilizing the AIE effect and the fluorescence resonance energy transfer (FRET) approach. This approach represents the first utilization of this composite for ratiometric detection. Nevertheless, upon the addition of P2O74-, the AIE and FRET processes were hindered due to the higher coordination interaction of Al3+ towards P2O74- compared to the amino/carboxyl groups on Al-N@CQDs. This successful interference of the AIE and FRET processes allowed for the effective estimation of P2O74-. The response ratio (F450/F620) increased with increasing the concentration of P2O74- in the range of 0.035-160 µM, with an impressive detection limit of 0.012 µM. This innovative approach of utilizing hybrid CQDs/thiolate-capped nanoclusters as a ratiometric fluorescent sensor for analytical applications introduces new possibilities in the field. The as-fabricated system was successfully applied to detect P2O74- in different real samples such as water, serum, and urine samples with acceptable results.

Multifunctional carbon dots originated from waste garlic peel for rapid sensing of heavy metals and fluorescent imaging of 2D and 3D spheroids cultured fibroblast cells

Here, we prepared sulfur and nitrogen self-doped carbon dots derived from garlic peel extract (GPSNCDs) using a hydrothermal method. The as-synthesized GPSNCDs were confirmed using Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analytical techniques indicate that the resulting GPSNCDs exhibit distinct emissive carbon-core with functionalities (owing to various ligands in the GPSNCDs). These functionalities are responsible for excellent hydrophilic and optical properties, including excitation-dependent emission and anti-photobleaching. Fluorescence intensities of GPSNCDs were quenched in the existence of Mn2+ and Fe3+ ions. This indicates that the GPSNCDs were sensitive to Fe3+ and Mn2+ ions with a limited range from 5 to 50 µM and showed lower recognition at ∼0.75 and 0.95 µM, respectively. In addition, the sensing results were generated in a short time (20 s). The cytotoxicity of GPSNCDs was tested to demonstrate that they are sufficiently safe to use for cellular imaging. The novel fluorescent GPSNCDs-based sensor can be used as a high-performance sensor for environmental monitoring. Further, GPSNCDs showed greater biocompatibility with normal fibroblast cells, and In Vitro fluorescent imaging of GPSNCDs revealed strong fluorescence signals in the two-dimensional (2D) and three-dimensional (3D) spheroids cultured fibroblast cells. The properties mentioned above demonstrate that the GPSNCDs can be applied to imaging normal cells without further modifications.

Selective detection of rutin at novel pyridinic-nitrogen-rich carbon dots derived from chicken feet biowaste: The role of bovine serum albumin during the assay

A simple fluorescence method is described for measuring rutin dependent on the nitogen-doped carbon dots (NCDs) prepared via simple pyrolysis method from chicken feet biowaste. The as-fabricated NCDs have unique advantages including cost-effectiveness and high quantum yield (42.9 %). The as-prepared NCDs explore an optimal emission band at 430 nm following exciting NCDs at 330 nm. Addition of rutin to blue-emissive NCDs quenched their fluorescence emission by inner-filtration effect (IFE) and static quenching. Under optimized conditions, the fluorescence responses increased as the rutin amount was raised from 100 to 1000 nmol/L with 5.3 nmol/L as a detection limit (S/N = 3). The probe selectivity was improved by adding bovine serum albumin (BSA), which binds other structurally-related compounds (other flavonoids). The as-synthesized NCDs exhibited some advantages towards rutin detection such as: lower LOD value, satisfactorily reproducibility, simplicity, rapidity, selectivity, and stability. The sensing probe was efficiently utilized for determining rutin in different real samples with acceptable results. The sensor offers an efficient biowaste-based approach for the determination of (bio) molecules.

Ratiometric fluorometric determination of sulfide using graphene quantum dots and self-assembled thiolate-capped gold nanoclusters triggered by aluminum

A ratiometric-based fluorescence emission system was proposed for the determination of sulfide. It consists of blue emissive graphene quantum dots (GQDs) and self-assembled thiolate-protected gold nanoclusters driven by aluminum ion (Al3+@GSH-AuNCs). The two types of fluorophores are combined to form a ratiometric emission probe. The orange emission of Al3+ @GSH-AuNCs at 624 nm was quenched in the presence of sulfide ion owing to the strong affinity between sulfide and Au(I), while the blue GQDs fluorescence at 470 nm remained unaffected. Interestingly, the Al3+@GSH-AuNCs and GQDs were excited under the same excitation wavelength (335 nm). The response ratios (F470/F624) are linearly proportional to the sulfide concentration within the linear range of 0.02-200 µM under the optimal settings, with a limit of detection (S/N = 3) of 0.0064 µM. The proposed emission probe was applied to detect sulfide ions in tap water and wastewater specimens, with recoveries ranging from 95.3% to 103.3% and RSD% ranging from 2.3% to 3.4%, supporting the proposed method's accuracy.

Colorimetric and fluorometric dual-mode determination of hypochlorite based on redox-mediated quenching

We have successfully created a dual-modal probe, labeled as of iron(ii)-ortho-phenanthroline/N, S@g-CDs, which combines both fluorometric and colorimetric techniques for the accurate and sensitive detection of hypochlorite (ClO-). The mechanism behind this probe involves the fluorescence quenching interaction between nitrogen and sulfur co-doped green emissive carbon dots (N, S@g-CDs) and the iron(ii)-ortho-phenanthroline chelate, utilizing both the inner filter effect and redox processes. As the concentration of ClO- increases, the iron(ii) undergo oxidation to iron(iii) as follows: Fe(ii) + 2HClO = Fe(iii) + Cl2O + H2O, leading to the restoration of N, S@g-CDs fluorescence. Simultaneously, the color of the system transitions gradually from red to colorless, enabling colorimetric measurements. In the fluorometric method with an excitation wavelength of 370 nm, the ClO- concentration exhibits a wide linear correlation with fluorescence intensity ranging from 0.07 to 220 μM. The detection limit achieved in this method is 0.02 μM (S/N = 3). In contrast, the colorimetric method exhibits a linear range of 1.12 to 200 μM, with a detection limit of 0.335 μM (S/N = 3). The proposed selective absorbance for this method is 510 nm. The probe has been effectively utilized for the detection of ClO- in various samples, including water and milk samples. This successful application showcases its potential for determining ClO- in complex matrices, highlighting its broad range of practical uses.

Electrochemistry of Flavonoids: A Comprehensive Review

Flavonoids represent a large group of aromatic amino acids that are extensively disseminated in plants. More than six thousand different flavonoids have been isolated and identified. They are important components of the human diet, presenting a broad spectrum of health benefits, including antibacterial, antiviral, antimicrobial, antineoplastic, anti-mutagenic, anti-inflammatory, anti-allergic, immunomodulatory, vasodilatory and cardioprotective properties. They are now considered indispensable compounds in the healthcare, food, pharmaceutical, cosmetic and biotechnology industries. All flavonoids are electroactive, and a relationship between their electron-transfer properties and radical-scavenging activity has been highlighted. This review seeks to provide a comprehensive overview concerning the electron-transfer reactions in flavonoids, from the point of view of their in-vitro antioxidant mode of action. Flavonoid redox behavior is related to the oxidation of the phenolic hydroxy groups present in their structures. The fundamental principles concerning the redox behavior of flavonoids will be described, and the phenol moiety oxidation pathways and the effect of substituents and experimental conditions on flavonoid electrochemical behavior will be discussed. The final sections will focus on the electroanalysis of flavonoids in natural products and their identification in highly complex matrixes, such as fruits, vegetables, beverages, food supplements, pharmaceutical compounds and human body fluids, relevant for food quality control, nutrition, and healthcare research.

Ratiometric sensing interface for glutathione determination based on electro-polymerized copper-coordinated molecularly imprinted layer supported on silver/porous carbon hybrid

A novel molecularly imprinted ratiometric-based sensor was designed for highly selective and ultrasensitive electrochemical detection of glutathione (GSH). The sensor consists of porous carbon co-doped with nitrogen and sulfur formed on the surface of graphite electrode (N, S@PC/GE). Silver nanoparticles (Ag) were grown on the surface of N, S@PC/GE to improve the conductivity/surface area of the sensor and represent an internal reference signal for ratiometric response. The monomer (pyrrole-4-carboxylic acid, Py-COOH) was electro-polymerized on the surface of Ag/N, S@PC/GE in the presence of Cu (II) to form Cu-MIP@Ag/N, S@PC/GE. Addition of GSH decreased the signal of Ag at 0.18 V (oxidation of Ag) due to coordination complexation, while the signal response at 0.83 V (oxidation of Ag-GSH complex) was increased. Under optimum conditions, the ratio response (I_GSH/I_Ag) was increased with increasing the concentration of GSH in the range of 0.01-500 nM with a detection limit (S/N = 3) of 0.003 nM. The electrochemical sensor exhibits many advantages including low LOD, high selectivity, good reproducibility, and satisfactory stability. The sensor was successfully applied to determine GSH in dietary supplements and human serum samples with recoveries % ranged from 97.4 to 101.8% and relative standard deviation % (RSD %) did not exceed 3.8%. This research paper introduces new information for the construction of molecular imprinted ratiometric-based electrochemical sensors for highly selective and sensitive detection of (bio) molecules.

Facile fabrication of boron and nitrogen co-doped carbon dots for "ON-OFF-ON" fluorescence sensing of Al3+ and F- ions in water samples

Water contamination with harmful ions has grown to be a significant environmental issue on a global scale. Therefore, the fabrication of simple, cost-effective, and reliable sensors is essential for identifying these ions. Herein, co-doping of carbon dots with new caffeine and H3BO3-derived boron (B) and nitrogen (N) was performed (BN@CDs). The as-prepared BN@CDs probe was used for the tandem fluorescence sensing of Al3+ and F- based on "ON-OFF-ON" switches. The BN@CDs nanoswitch has a high quantum yield of 44.8% with λexc. and λem. of 360 nm and 440 nm, respectively. The probe exhibited good stability with different pH, ionic-strengths, and irradiation times. The fluorescence emission of BN@CDs was decreased as the Al3+ concentration was increased with a linear range of 0.03-90 μM and a limit of detection (S/N = 3) equal to 9.0 nM. Addition of F- restored the BN@CDs emission as F- ions form a strong and stable complex with Al3+ ions [Al(OH)3F]-. Therefore, the ratio response (F/F°) was raised by raising the F- ion concentration to the range of 0.18-80 μM with a detection limit (S/N = 3) of 50.0 nM. The BN@CDs sensor exhibits some advantages over other reported methods in terms of simplicity, high quantum yield, and low detection limit. Importantly, the sensor was successfully applied to determine Al3+ and F- in various ecological water specimens with accepted results.

A new class of layered Bi2O2S nanopetals by one-pot supercritical-CO2 approach: A reliable electrocatalyst for analgesic bioflavonoid detection

Nanomaterials frequently draw a lot of interest in a variety of disciplines, including electrochemistry. Developing a reliable electrode modifier for the selective electrochemical detection of the analgesic bioflavonoid i.e., Rutinoside (RS) is a great challenge. Here in, we have explored the supercritical-CO₂ (SC-CO₂) mediated synthesis of bismuth oxysulfide (SC-BiOS) and reported it as a robust electrode modifier for the detection of RS. For a comparison study, the same preparation procedure was carried out in the conventional approach (C-BiS). The morphology, crystallography, optical, and elemental contribution analyses were characterized to understand the paradigm shift in the physicochemical properties between SC-BiOS and C-BiS. The results exposed the C-BiS had a nano-rod-like structure with a crystallite size of 11.57 nm; whereas the SC-BiOS had a nano-petal-like structure with a crystallite size of 9.03 nm. The B_2g mode in the optical analysis confirms the formation of bismuth oxysulfide by the SC-CO₂ method with the Pmnn space group. As an electrode modifier, the SC-BiOS achieved a higher effective surface area (0.074 cm²), higher electron transfer kinetics (0.13 cm s^-1), and lower charge transfer resistance (403 Ω) than C-BiS. Further, it provided a wide linear range of 0.1-610.5 μM L^-1 with a low detection and quantification limit of 9 and 30nM L^-1 and an appreciable sensitivity of 0.706 μA μM^-1 cm^-2. The selectivity, repeatability, and real-time application towards the environmental water sample with a recovery of 98.87% were anticipated for the SC-BiOS. This SC-BiOS unlocks a fresh avenue to construct a design for the family of electrode modifiers utilized in electrochemical applications.

Bifunctional ratiometric sensor based on highly fluorescent nitrogen and sulfur biomass-derived carbon nanodots fabricated from manufactured dairy product as a precursor

Novel biomass-derived carbon dots co-doped with nitrogen and sulfur were fabricated through facile and simple synthetic method from manufactured milk powder and methionine as precursors. The as-fabricated platform was used for ratiometric fluorescence sensing of Cu (II) and bisphosphonate drug risedronate sodium. The sensing platform is based on oxidation of o-phenylenediamine by Cu (II) to form 2, 3-diaminophenazine (oxidized product) with an emission peak at 557 nm. The resultant product quenched the fluorescence emission of as-fabricated carbon dots at 470 nm through Förster resonance energy transfer (FRET) and inner-filter effect (IFE). Upon addition of risedronate sodium, the formation of 2, 3-diaminophenazine was decreased as a result of Cu (II) chelation with risedronate sodium, recovering the fluorescence emission of carbon dots. The ratio of fluorescence at 470 nm and 557 nm was measured as a function of Cu (II) and risedronate sodium concentrations. The proposed sensing platform sensitively detected Cu (II) and risedronate sodium in the range of 0.01-55 μM and 5.02-883 µM with LODs (S/N = 3) of 0.003 μM and 1.48 µM, respectively. The sensing platform exhibited a good selectivity towards Cu (II) and risedronate sodium. The sensing system was used to determine Cu (II) and risedronate sodium in different sample matrices with recoveries % in the range of 99-103 % and 97.4-103.8 %, and RSDs % in the range of 1.5-3.0 % and 1.8-3.6 %, respectively.

Determination of trace amount of iron cations using electrochemical methods at N, S doped GQD modified electrode

In this work, nitrogen and sulfur co-doped graphene quantum dot-modified glassy carbon electrodes (N, S-GQD/GCE) were used for the recognition of iron cations in aqueous solutions. The dissolved cations are detected based on the faradaic reduction or oxidation current of Fe(III) and Fe(II) obtained at the N, S-GQD/GCE surface. Cyclic voltammetry (CV), square wave voltammetry (SWV), and hydrodynamic amperometry are used as suitable electrochemical techniques for studying electrochemical behavior and determination of Fe cations. Based on the obtained results, it is concluded that the presence of free electrons in the structure of N, S-GQD could facilitate electron transfer reaction between Fe(III) and electrode surface which with increased surface area results in increased sensitivity and lower limit of detection. By performing suitable experiments, the best condition for preparing the modified electrode and determining Fe(III) was selected. Under optimized conditions, the amperometric response is linear from 1 to 100 nM of Fe(III) with a detection limit of 0.23 nM. The validity of the method and applicability of the sensor is successfully tested by the determination of Fe(III) in drug and water real samples. This sensor opened a new platform based on doped nanoparticles for highly sensitive and selective detection of analytes.

Nitrogen and Sulfur Co-doped Carbon Dots as a Turn-Off Fluorescence Probe for the Detection of Cerium and Iron

Carbon dots has becoming one of the most promising fluorescence sensors to determine the trace level of heavy metals in environments because of their advantages in optical properties, response time, and convenient operation procedures. Herein, a novel nitrogen and sulfur co-doped carbon dots (NS-CDs) were prepared though microwave assisted approach using DL-malic acid and allyl thiourea for the first time. Due to the existence of nitrogen and sulfur, the as-prepared NS-CDs exhibited bright blue fluorescence at 430 nm upon 330 nm excitation, with a fluorescence quantum yield of 19.8%. The sensitivity study of NS-CDs against metal ions and organic molecules has approved that the fluorescence could be further quenched by Ce⁴⁺ and Fe³⁺ ions, with the same linear detection ranges varying from 10 to 90 µM. The limits of detection (LOD) were determined as low as 0.75 µM and 0.67 µM for Ce⁴⁺ and Fe³⁺ ions, respectively. The possible quenching mechanism is explained by inner filter effect and static quenching mechanism for Ce⁴⁺ ions, while the quenching effect caused by Fe³⁺ ions is attributed to the inner filter effect, static and dynamic quenching mechanisms. Additionally, the developed sensor was used for the detection of Ce⁴⁺ and Fe³⁺ ions in tap water with satisfactory recoveries. Finally, the designed NS-CDs sensor possesses good biocompatibility against MA104 cells, suggesting the sensor can be potentially applied to detect Ce⁴⁺ and Fe³⁺ ions in environment and biological systems.