A review of the identification and detection of heavy metal ions in the environment by voltammetry

Electrochemical real-time sensor for the detection of Pb(II) ions based on Ti3C2Tx MXene

Lead ions are especially harmful to human health, causing significant developmental and behavioral abnormalities even at small concentrations. In real-life samples, lead ions are present in mixtures with other metal ions, creating a challenge to detect it selectively at low quantities. To address these challenges, we prepared an electrochemical sensor based on delaminated Ti3C2Tx MXene, which can selectively detect low concentrations of Pb2+ in a solution containing other common metal ions. Cyclic voltammetry was applied as an electrochemical detection method. The proposed reaction mechanism involves a reversible transition between Pb2+ ions and PbO at the MXene-based layer. The sensitivity of the sensor towards Pb2+ ions and a limit of detection were determined. The sensor, as prepared, had a linear response range within 0.15-1.0 μM, with a sensitivity of 26.7 μA/μM and LOD value of 48.7 nM, which meets the requirements set by the World Health Organization.

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 μM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Preparation of pyridoxine-based polyurethane modified sensors and their use in simultaneous determination of Cu(II) - Co(II) ions

In this study, pyridoxine-based polyurethane-modified electrodes were prepared to simultaneously and sensitively measure copper (Cu(II)) and cobalt (Co(II)) ions in complex matrix samples. For the production of the electrodes, firstly, the synthesis of pyridoxine-based polyurethane structures was carried out. In these syntheses, the polymer structure was diversified by using different isocyanates. Polyethyleneglycol-200 (PEG), pyridoxine (B6), and β-cyclodextrin (β-CD) groups were used as the source of polyol. The synthesized polyurethane structures were characterized by different instrumental techniques and used in gold electrode surface modification. Modified sensor surfaces were examined by scanning electron microscopy and atomic force microscopy techniques. The prepared modified sensors were used for the simultaneous detection of Cu(II) and Co(II) ions using the differential pulse voltammetry technique. The limit of detection (LOD), limit of quantitation (LOQ), and R2 values for Cu(II) ions were calculated as 8.81 μM, 29.4 μM, and 0.993, respectively. LOD, LOQ, and R2 values for Co(II) ions were calculated as 9.84 μM, 32.8 μM, and 0.9935, respectively. For repeatability, the relative standard deviation (RSD %) of the prepared simultaneous sensors was determined as 1.54 and 1.71 for Cu(II) and Co(II), respectively. As a result, Cu(II) and Co(II) ions were measured independently and simultaneously with high sensitivity. According to these results, it is predicted that pyridoxine-based polyurethane-modified sensors may be suitable for the simultaneous detection of Cu(II) and Co(II) in medical, food, and agricultural samples.

Emerging insights into the application of metal-organic framework (MOF)-based materials for electrochemical heavy metal ion detection

Heavy metal ions are one of the main sources of water pollution, which has become a major global problem. Given the growing need for heavy metal ion detection, electrochemical sensor stands out for its high sensitivity and efficiency. Metal-organic frameworks (MOFs) have garnered much interest as electrode modifiers for electrochemical detection of heavy metal ions owing to their significant specific surface area, tailored pore size, and catalytic activity. This review summarizes the progress of MOF-based materials, including pristine MOFs and MOF composites, in the electrochemical detection of various heavy metal ions. The synthetic methods of pristine MOFs, the detection mechanisms of heavy metal ions and the modification strategies of MOFs are introduced. Besides, the diverse applications of MOF-based materials in detecting both single and multiple heavy metal ions are presented. Furthermore, we present the current challenges and prospects for MOF-based materials in electrochemical heavy metal ion detection.

Synthesis of ZIF-8/chitosan composites for Cu2+ removal from water

In this work, a kind of novel Chitosan (Cs)-doped zeolite imidazole framework (ZIF-8@Cs) with a larger surface area and a smaller pore size was synthesised via a facial solvothermal approach and applied to remove Cu2+ from mine wastewater. Compared to nondoped ZIF-8, ZIF-8@Cs exhibited a stronger adsorption performance and removal efficiency. The reason was that ZIF-8@Cs doped by the Cs could suppress the aggregation and increase the monodispersity of ZIF-8. Using the high-performance ZIF-8@Cs, as a novel adsorbent, was successfully developed for the efficient removal of Cu2+ from mine wastewater. Various parameters, such as contact time, initial Cu2+ concentration, adsorbent dosage, and pH, were investigated. The results showed that a removal efficiency of 85% was obtained at 4 h contact time for a Cu2+ concentration of 30 mg/L at the optimum pH of 6.0. Equilibrium data were analysed using different isothermal models and kinetic models, analytic results indicated that the capture of Cu2+ by ZIF-8@Cs could favourably comply with the pseudo-first-order kinetic model and Langmuir isotherm model. The single-layer adsorption of Cu2+ on ZIF-8@Cs was dominated by diffusional mass transfer. Additionally, the results of the thermodynamic analysis indicated that the adsorption of Cu2+ by ZIF-8/Cs was a spontaneous, exothermic, and ordered process. Overall, the results reported herein indicated that ZIF-8/Cs with high adsorption efficiency are very attractive and imply a potential practical application for the removal of potentially toxic elements in wastewater.

Kinetics, Thermodynamics, and Mechanistic Studies of Arsenic Removal Utilizing Natural Soil as Adsorbent

The contamination of water sources with the heavy metal contaminant arsenic (As) causes substantial risks to humans, animals, and other living organisms. Therefore, the introduction of methods for the removal of As is important. The present study aimed to investigate the adsorption model and mechanism of As removal utilizing natural soil adsorbents. The batch adsorption technique was used to analyze the impacts of various parameters such as contact time, initial As concentration, pH, and temperature. Adsorption mechanisms were studied through adsorption kinetic, isotherm, and thermodynamic models. The batch adsorption study findings indicate that the optimal conditions for maximum As removal were achieved by application of 2.2 g of adsorbents in 50 μg/L of As solution for 60 min of contact time at a pH of 5.5 ± 0.5 and a temperature of 40 °C. The highest removal efficiency was achieved when red soil was employed as the adsorbent. The kinetic, isotherm, and thermodynamic models revealed that As adsorption was a chemisorptive, nonspontaneous, and endothermic process.

Hydrogen-bond organic-framework-based electrochemical sensor for highly sensitive determination of trace cadmium ions in environmental and e-cigarette samples

BACKGROUND

The heavy metal ion Cd2+ is acutely toxic, and excessive concentrations can have adverse effects on human production and life, and even lead to significant public health risks and environmental impacts. There are several mature non-electrochemical methods for heavy metal detection, but these methods are characterized by high cost, which makes it difficult to be applied to the field for timely detection. Therefore, it is necessary to prepare a new electrochemical sensor that is environmentally friendly and capable of detecting Cd2+ in the environment quickly, easily and sensitively.

RESULTS

In this study, hydrogen-bonded organic frameworks (HOFs) were synthesized by a simple hydrothermal reaction. The prepared materials consisted of only C, N and O and had a thin lamellar structure. The HOFs were integrated into a novel electrochemical sensor to achieve accurate detection of Cd2+ ions in real aqueous environments by square wave anodic dissolution voltammetry. The sensor has a wide linear range and a detection limit as low as 0.13 μg/L. Several real water samples, such as tap water, lake water, and e-cigarette digest, were analyzed to simulate the working environment of the sensor, and the results showed that the recoveries of Cd2+ ranged from 95.75 % to 101.2 %.

SIGNIFICANCE

We pioneered the detection of heavy metal ions Cd2+ in e-cigarette digestate samples with the innovative use of HOFs as the sensor material, which demonstrated the potential application in electrochemical sensing with extremely low background current value and high sensitivity, providing new ideas for environmental monitoring and public health control.

Nanoporous Gold-Modified Screen-Printed Electrodes for the Simultaneous Determination of Pb2+ and Cu2+ in Water

In this study, nanoporous gold (NPG) was deposited on a screen-printed carbon electrode (SPCE) by the dynamic hydrogen bubble template (DHBT) method to prepare an electrochemical sensor for the simultaneous determination of Pb2+ and Cu2+ by square wave anodic stripping voltammetry (SWASV). The electrodeposition potential and electrodeposition time for NPG/SPCE preparation were investigated thoroughly. Scanning electron microscopy (SEM) and energy-dispersive X-ray diffraction (EDX) analysis confirmed successful fabrication of the NPG-modified electrode. Electrochemical characterization exhibits its superior electron transfer ability compared with bare and nanogold-modified electrodes. After a comprehensive optimization, Pb2+ and Cu2+ were simultaneously determined with linear range of 1-100 μg/L for Pb2+ and 10-100 μg/L for Cu2+, respectively. The limits of detection were determined to be 0.4 μg/L and 5.4 μg/L for Pb2+ and Cu2+, respectively. This method offers a broad linear detection range, a low detection limit, and good reliability for heavy metal determination in drinking water. These results suggest that NPG/SPCE holds great promise in environmental and food applications.

In situ deposition of bismuth on pre-anodized screen-printed electrode for sensitive determination of Cd2+ in water and rice with a portable device

Electrochemical detection is favorable for the rapid and sensitive determination of heavy metal cadmium. However, the detection sensitivity needs to be further improved, and a portable, low-cost device is needed for on-site detection. Herein, an in-situ bismuth modified pre-anodized screen-printed carbon electrode (SPCE) was developed for Cd2+ determination by square wave anodic stripping voltammetry (SWASV). The in-situ bismuth modification enhances the enrichment of Cd2+, and together with pre-anodization improve the electron transfer rate of electrode, thus enhancing the detection sensitivity. The electrode modification method combines pre-anodization and in-situ bismuth deposition, which is very easy and effective. Furthermore, a self-made PSoC Stat potentiostat coupled with a stirring device was fabricated for portable and low-cost electrochemical detection. After comprehensive optimization, the developed method can reach a testing time of 3 min, a detection limit of 3.55 μg/L, a linear range of 5-100 μg/L, and a recovery rate of 91.7-107.1% in water and rice samples for Cd2+ determination. Therefore, our method holds great promise for the rapid, sensitive and on-site determination of Cd2+ in food samples.

Sensing with Molecularly Imprinted Membranes on Two-Dimensional Solid-Supported Substrates

Molecularly imprinted membranes (MIMs) have been a focal research interest since 1990, representing a breakthrough in the integration of target molecules into membrane structures for cutting-edge sensing applications. This paper traces the developmental history of MIMs, elucidating the diverse methodologies employed in their preparation and characterization on two-dimensional solid-supported substrates. We then explore the principles and diverse applications of MIMs, particularly in the context of emerging technologies encompassing electrochemistry, surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), and the quartz crystal microbalance (QCM). Furthermore, we shed light on the unique features of ion-sensitive field-effect transistor (ISFET) biosensors that rely on MIMs, with the notable advancements and challenges of point-of-care biochemical sensors highlighted. By providing a comprehensive overview of the latest innovations and future trajectories, this paper aims to inspire further exploration and progress in the field of MIM-driven sensing technologies.

Generating robust aptamers for food analysis by sequence-based configuration optimization

Advanced analytical techniques are emerging in the food industry. Aptamer-based biosensors achieve rapid and highly selective analysis, thus drawing particular attention. Aptamers are oligonucleotide probes screened via in vitro Systematic Evolution of Ligands by EXponential Enrichment (SELEX), which can bind with their specific targets by folding into three-dimensional configurations and accept various modifications to be incorporated into biosensors, showing great potential in food analysis. Unfortunately, aptamers obtained by SELEX may not possess satisfactory affinity. Post-SELEX strategies were proposed to optimize aptamers' configuration and enhance the binding affinity, with specificity confirmed. Sequence-based optimization strategies exhibit great advantages in simple operation, good generalization, low cost, etc. This review summarizes the latest study (2015-2023) on generating robust aptamers for food targets by sequence-based configuration optimization, as well as the generated aptamers and aptasensors, with an expectation to provide inspirations for developing aptamer and aptasensors with high performance for food analysis and to safeguard food quality and safety.

Simultaneous Determination of Chemical Oxygen Demand, Total Nitrogen, Ammonia, and Phosphate in Surface Water Based on a Multielectrode System

A technique for monitoring chemical oxygen demand (COD), total nitrogen (TN), ammonia (N-NH4), and phosphate (P-PO4) in surface water with a targeted signal multielectrode system (Cu, Ir, Rh, Co(OH)2, and Zr(OH)4 electrodes) is proposed for the first time. Each water quality index is specifically detected by at least two electrodes with distinct selectivity sensing mechanisms. Cyclic voltammetry and electrochemical impedance measurements are employed for multidimensional signal acquisition, complemented by normalization and Least Absolute Shrinkage and Selection Operator (LASSO) for principal feature extraction and dimension reduction. Multiple linear regression (MLR), partial least-squares (PLS), and eXtreme Gradient Boosting (XGBoost) were employed to evaluate the established prediction model. The precisions of the multielectrode system are ±10%/±5 ppm of COD, ±10%/±0.2 ppm of TN, ±5%/±0.1 ppm of N-NH4, and ±5%/±0.01 ppm of P-PO4. The analysis time of the multielectrode system is reduced from hours to minutes compared with traditional analysis, without any sample pretreatment, facilitating continuous online monitoring in the field. The developed multielectrode system offers a feasible strategy for online in situ monitoring of surface water quality.

Effect of Temperature on the Removal of Interferences in the Voltammetric Procedure for the Determination of Cr(VI)

The aim of this paper was to investigate the effect of temperature on the removal efficiency of surfactant-induced interferences. Surfactants were removed as a result of mixing with XAD-7 resin. The study was carried out using the example of Cr(VI) determination by adsorption stripping voltammetry (AdSV). Measurements were carried out using a solution containing Cr(VI), acetate buffer (pH = 6.2), DTPA, KNO3, and different surfactants. Ten mL of the solution was mixed with 0.5 g of XAD-7 resin at different temperatures for 5 min prior to voltammetric measurement. The effect of the mixing temperature of the sample with the resin on the voltammetric Cr(VI) signal in the presence of different surfactants was studied in the range from 20 to 60 °C. The proposed method of removing interference from surfactants by mixing the sample with the XAD-7 resin at 60 °C was used for the determination of trace amounts of Cr(VI) in river water containing non-ionic, anionic, cationic surfactants, and biosurfactants.

Bismuth Film along with dsDNA-Modified Electrode Surfaces as Promising (bio)Sensors in the Analysis of Heavy Metals in Soils

Heavy metals constitute pollutants that are particularly common in air, water, and soil. They are present in both urban and rural environments, on land, and in marine ecosystems, where they cause serious environmental problems since they do not degrade easily, remain almost unchanged for long periods, and bioaccumulate. The detection and especially the quantification of metals require a systematic process. Regular monitoring is necessary because of seasonal variations in metal levels. Consequently, there is a significant need for rapid and low-cost metal determination methods. In this study, we compare and analytically validate absorption spectrometry with a sensitive voltammetric method, which uses a bismuth film-plated electrode surface and applies stripping voltammetry. Atomic absorption spectroscopy (AAS) represents a well-established analytical technique, while the applicability of anodic stripping voltammetry (ASV) in complicated sample matrices such as soil samples is currently unknown. This sample-handling challenge is investigated in the present study. The results show that the AAS and ASV methods were satisfactorily correlated and showed that the metal concentration in soils was lower than the limit values but with an increasing trend. Therefore, continuous monitoring of metal levels in the urban complex of a city is necessary and a matter of great importance. The limits of detection of cadmium (Cd) were lower when using the stripping voltammetry (SWASV) graphite furnace technique compared with those obtained with AAS when using the graphite furnace. However, when using flame atomic absorption spectroscopy (flame-AAS), the measurements tended to overestimate the concentration of Cd compared with the values found using SWASV. This highlights the differences in sensitivity and accuracy between these analytical methods for detecting Cd. The SWASV method has the advantage of being cheaper and faster, enabling the simultaneous determination of heavy elements across the range of concentrations that these elements can occur in Mediterranean soils. Additionally, a dsDNA biosensor is suggested for the discrimination of Cu(I) along with Cu(II) based on the oxidation peak of guanine, and adenine residues can be applied in the redox speciation analysis of copper in soil, which represents an issue of great importance.

Underground Ink: Printed Electronics Enabling Electrochemical Sensing in Soil

Improving agricultural production relies on the decisions and actions of farmers and land managers, highlighting the importance of efficient soil monitoring techniques for better resource management and reduced environmental impacts. Despite considerable advancements in soil sensors, their traditional bulky counterparts cause difficulty in widespread adoption and large-scale deployment. Printed electronics emerge as a promising technology, offering flexibility in device design, cost-effectiveness for mass production, and a compact footprint suitable for versatile deployment platforms. This review overviews how printed sensors are used in monitoring soil parameters through electrochemical sensing mechanisms, enabling direct measurement of nutrients, moisture content, pH value, and others. Notably, printed sensors address scalability and cost concerns in fabrication, making them suitable for deployment across large crop fields. Additionally, seamlessly integrating printed sensors with printed antenna units or traditional integrated circuits can facilitate comprehensive functionality for real-time data collection and communication. This real-time information empowers informed decision-making, optimizes resource management, and enhances crop yield. This review aims to provide a comprehensive overview of recent work related to printed electrochemical soil sensors, ultimately providing insight into future research directions that can enable widespread adoption of precision agriculture technologies.

Electrochemical sensors modified with iron oxide nanoparticles/nanocomposites for voltammetric detection of Pb (II) in water: A review

Permissible limits of Pb2+ in drinking water are being reduced from 10 μgL-1 to 5 μgL-1, which calls for rapid, and highly reliable detection techniques. Electrochemical sensors have garnered attention in detection of heavy metal ions in environmental samples due to their ease of operation, low cost, and rapid detection responses. Selectivity, sensitivity and detection capabilities of these sensors, can be enhanced by modifying their working electrodes (WEs) with iron oxide nanoparticles (IONPs) and/or their composites. Therefore, this review is an in-depth analysis of the deployment of IONPs/nanocomposites in modification of electrochemical sensors for detection of Pb2+ in drinking water over the past decade. From the analyzed studies (n = 23), the optimal solution pH, deposition potential, and deposition time ranged between 3 and 5.6, -0.7 to -1.4 V vs Ag/AgCl, and 100-400 s, respectively. Majority of the studies employed square wave anodic stripping voltammetry (n = 16), in 0.1 M acetate buffer solution (n = 19) for detection of Pb2+. Limits of detection obtained (2.5 x 10-9 - 4.5 μg/L) were below the permissible levels which indicated good sensitivities of the modified electrodes. Despite the great performance of these modified electrodes, the primary source of IONPs has always been commercial iron-based salts in addition to the use of so many materials as modifying agents of these IONPs. This may limit reproducibility and sustainability of the WEs due to lengthy and costly preparation protocols. Steel and/or iron industrial wastes can be alternatively employed in generation of IONPs for modification of electrochemical sensors. Additionally, biomass-based activated carbons enriched with surface functional groups are also used in modification of bare IONPs, and subsequently bare electrodes. However, these two areas still need to be fully explored.

A simple, fast and inexpensive approach to quantify low concentrations of iron in biodiesel by voltammetry after extraction induced by microemulsion breaking

An alternative approach to assay iron (Fe) in biodiesel by differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) is presented herein. The sample treatment involved a simple, rapid, but effective extraction of Fe from biodiesel into an aqueous phase after microemulsion (ME) breaking. Then, Fe was determined as the complex Fe(III)-PAN (1-(2-pyridylazo)-2-naphthol) on a glassy carbon electrode (GCE) in the presence of bismuth (Bi(III)). The extraction induced by microemulsion breaking (EIMB) was achieved by adding 0.80 mL of ultrapure water into a water-in-oil ME containing 7.00 mL biodiesel, 2.70 mL n-propanol and 0.30 mL of 0.25 mol L-1 HNO3 solution. No deliberate addition of surfactant was necessary to form and maintain the ME. The EIMB resulted in a 1.30 mL lower aqueous phase extract (APhEx) and an upper oily phase. DP voltammograms were recorded with a portable potentiostat, showing the potentiality of carrying out the determination out of a central laboratory. Another feature was the non-necessity of deaerating the solution to eliminate the dissolved O2. The limits of detection (LOD) and quantification (LOQ) were 1.7 μg L-1 (140 mg kg-1) and 5.5 μg L-1 (455 mg kg-1), respectively. The accuracy of the method was evaluated by recovery assays of spiked samples, by analyzing a standard reference material and by comparisons with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS).

Study on the affinity sites of cadmium's binding to ligands by thermodynamics and nuclear magnetic resonance spectroscopy

The affinity sites of cadmium (Cd(II)) when binding to cysteine (Cys) and glutathione (GSH) were studied via thermodynamics and nuclear magnetic resonance (NMR) spectroscopy methods. The results showed that the Cd(II) binding sites of Cys and GSH were -SH (exothermic), -NH2 (endothermic) and -COOH (endothermic). The thermodynamic behaviour of Cd(II) binding to Cys/GSH in boric acid and HEPES buffers differed, with the former being mainly endothermic and the latter mainly exothermic. It could be inferred that, in the boric acid system, the main binding site of Cd(II) with Cys and GSH is changed from -SH in HEPES to -COOH and -NH2 in boric acid. This was confirmed by the results of NMR experiments of Cd(II) with Cys/GSH. 1D 1H-NMR experiments showed that, after the combination of Cd(II) and Cys, the changes in the chemical shifts and peak strengths of protons near the -SH group for the reaction in HEPES were greater than when boric acid buffer was used. Changes in the chemical shift and peak strength of the -NH2 protons due to the binding of Cd(II) to GSH were evident in the boric acid buffer but not in HEPES. The screening of functional monomers is very important in the process of preparation of cadmium ion-imprinted materials. This research provides important theoretical and experimental guidance for the screening of functional monomers.

Recent Advancements and Future Prospects in NBD-Based Fluorescent Chemosensors: Design Strategy, Sensing Mechanism, and Biological Applications

In recent years, the field of Supramolecular Chemistry has witnessed tremendous progress owing to the development of versatile optical sensors for the detection of harmful biological analytes. Nitrobenzoxadiazole (NBD) is one such scaffold that has been exploited as fluorescent probes for selective recognition of harmful analytes and their optical imaging in various cell lines including HeLa, PC3, A549, SMMC-7721, MDA-MB-231, HepG2, MFC-7, etc. The NBD-derived molecular probes are majorly synthesized from the chloro derivative of NBD via nucleophilic aromatic substitution. This general NBD moiety ligation method to nucleophiles has been leveraged to develop various derivatives for sensing analytes. NBD-derived probes are extensively used as optical sensors because of remarkable properties like excellent stability, large Stoke's shift, high efficiency and stability, visible excitation, easy use, low cost, and high quantum yield. This article reviewed NBD-based probes for the years 2017-2023 according to the sensing of analyte(s), including cations, anions, thiols, and small molecules like hydrogen sulfide. The sensing mechanism, designing of the probe, plausible binding mechanism, and biological application of chemosensors are summarized. The real-time application of optical sensors has been discussed by various methods, such as paper strips, molecular logic gates, smartphone detection, development of test kits, etc. This article will update the researchers with the in vivo and in vitro biological applicability of NBD-based molecular probes and challenges the research fraternity to design, propose, and develop better chemosensors in the future possessing commercial utility.

The Impact of Ar or N2 Atmosphere on the Structure of Bi-Fe-Carbon Xerogel Based Composites as Electrode Material for Detection of Pb2+ and H2O2

In this study, bismuth- and iron-embedded carbon xerogels (XG) were obtained using a modified resorcinol formaldehyde sol-gel synthesis method followed by additional enrichment with iron content. Pyrolysis treatment was performed at elevated temperatures under Ar or N2 atmosphere to obtain nanocomposites with different reduction yields (XGAr or XGN). The interest was focused on investigating the extent to which changes in the pyrolysis atmosphere of these nanocomposites impact the structure, morphology, and electrical properties of the material and consequently affect the electroanalytical performance. The structural and morphological particularities derived from X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) measurements revealed the formation of the nanocomposite phases, mostly metal/oxide components. The achieved performances for the two modified electrodes based on XG treated under Ar or N2 atmosphere clearly differ, as evidenced by the electroanalytical parameters determined from the detection of heavy metal cations (Pb2+) or the use of the square wave voltammetry (SWV) technique, biomarkers (H2O2), or amperometry. By correlating the differences obtained from electroanalytical measurements with those derived from morphological, structural, and surface data, a few utmost important aspects were identified. Pyrolysis under Ar atmosphere favors a significant increase in the α-Fe2O3 amount and H2O2 detection performance (sensitivity of 0.9 A/M and limit of detection of 0.17 μM) in comparison with pyrolysis under N2 (sensitivity of 0.5 A/M and limit of detection of 0.36 μM), while pyrolysis under N2 atmosphere leads to an increase in the metallic Bi amount and Pb2+ detection performance (sensitivity of 8.44 × 103 A/M and limit of detection of 33.05 pM) in comparison with pyrolysis under Ar (sensitivity of 6.47·103 A/M and limit of detection of 46.37 pM).

Phenothiazine-based fluorescent probes for the detection of hydrazine in environment and living cells

As an important chemical raw material, hydrazine brings convenience to people's lives and provides opportunities for human development. However, the misuse or leakage of hydrazine has brought pollution to the environment, including water, soil and living organisms. At the same time, hydrazine poses a potential threat to human health as a carcinogen. Despite the enormous challenges, it is crucial to develop an effective method to detect hydrazine in environmental samples. In this work, we have synthesized a series of probes based on phenothiazine fluorophore by the introduction of different substituents and developed a novel probe for the detection of hydrazine. The probe is capable of detecting hydrazine in aqueous solutions with high sensitivity and selectivity, and can be easily fabricated into paper test strips for use in in situ samples. In addition, the probe is effective in detecting hydrazine in water, soil, cells, and zebrafish, providing an excellent tool for detecting hydrazine in the environment.

Exploitation of environmental DNA (eDNA) for ecotoxicological research: A critical review on eDNA metabarcoding in assessing marine pollution

The rise in worldwide population has led to a noticeable spike in the production, consumption, and transportation of energy and food, contributing to elevated environmental pollution. Marine pollution is a significant global environmental issue with ongoing challenges, including plastic waste, oil spills, chemical pollutants, and nutrient runoff, threatening marine ecosystems, biodiversity, and human health. Pollution detection and assessment are crucial to understanding the state of marine ecosystems. Conventional approaches to pollution evaluation usually represent laborious and prolonged physical and chemical assessments, constraining their efficacy and expansion. The latest advances in environmental DNA (eDNA) are valuable methods for the detection and surveillance of pollution in the environment, offering enhanced sensibility, efficacy, and involvement. Molecular approaches allow genetic information extraction from natural resources like water, soil, or air. The application of eDNA enables an expanded evaluation of the environmental condition by detecting both identified and unidentified organisms and contaminants. eDNA methods are valuable for assessing community compositions, providing indirect insights into the intensity and quality of marine pollution through their effects on ecological communities. While eDNA itself is not direct evidence of pollution, its analysis offers a sensitive tool for monitoring changes in biodiversity, serving as an indicator of environmental health and allowing for the indirect estimation of the impact and extent of marine pollution on ecosystems. This review explores the potential of eDNA metabarcoding techniques for detecting and identifying marine pollutants. This review also provides evidence for the efficacy of eDNA assessment in identifying a diverse array of marine pollution caused by oil spills, harmful algal blooms, heavy metals, ballast water, and microplastics. In this report, scientists can expand their knowledge and incorporate eDNA methodologies into ecotoxicological research.

A Review on Recent Trends and Future Developments in Electrochemical Sensing

Electrochemical methods and devices have ignited prodigious interest for sensing and monitoring. The greatest challenge for science is far from meeting the expectations of consumers. Electrodes made of two-dimensional (2D) materials such as graphene, metal-organic frameworks, MXene, and transition metal dichalcogenides as well as alternative electrochemical sensing methods offer potential to improve selectivity, sensitivity, detection limit, and response time. Moreover, these advancements have accelerated the development of wearable and point-of-care electrochemical sensors, opening new possibilities and pathways for their applications. This Review presents a critical discussion of the recent developments and trends in electrochemical sensing.

Field determination and ecological health risk assessment of trace metals in typical mariculture area of China

Field determination of dissolved trace metals (Cu, Pb and Cd) by using automated electrochemical system had been done in three typical mariculture areas of Yellow Sea (YS), East China Sea (ECS) and South China Sea (SCS) in China. Higher concentrations of Cu and Pb were found in ECS while the Cd concentration showed a decreasing trend from north to south of China. The metal distribution and ecological health risk assessments were also conducted. Cu and Pb in the YS and Cu in SCS were moderately contaminated. ECS had considerable Cu contamination and very high Pb contamination. Compared with other coastal areas, mariculture affected the concentration and spatial distribution of trace metals, but it was not a necessarily dominant factor. Overall, the results contribute to the further development of field and on-board metal detection technology and lay a foundation for the realization of field ecological health risk assessments of mariculture waters.

Screen-Printed Sensors Modified with Nafion and Mesoporous Carbon for Electrochemical Detection of Lead in Blood

Lead (Pb) has long been acknowledged as a systemic toxicant, with pronounced health impacts observed even at low exposure levels, particularly in children. Adverse effects include diminished cognitive function, altered behavior, and developmental delays. Consequently, it is imperative to conduct regular monitoring of Blood Lead Levels (BLLs). In this work, we report on an electrochemical sensor based on screen-printed carbon electrode (SPCE) coated with Nafion and mesoporous carbon (MC). The sensor system uses simple sample preparation (acidification and dilution of whole blood), minimal sample volume (a few blood drops, 200 μl), and swift time-to-results (1 h). A limit of quantitation (LOQ) of 0.3 μg dL-1 Pb was achieved in whole blood. To demonstrate the practical utility of our sensor system, we evaluated its performance in the analysis of blood samples collected from children (n = 25). Comparative analysis with the laboratory-based gold standard method of inductively coupled plasma mass spectrometry (ICP-MS) demonstrated approximately 77% accuracy and 94% precision. We anticipate that our approach will serve as a valuable tool for more frequent BLL monitoring, particularly in communities where access to laboratory testing is impractical or expensive.

Regenerable and Highly Stable Two-Dimensional Imine-Based Covalent Organic Framework for Simultaneous Rapid Detection and Adsorption of Cu2+ Ions

The development of efficient fluorescent probes and adsorbents for detecting and removing Cu2+, which pose potential environmental and health risks, is a highly active area of research. However, achieving simultaneously improved fluorescence detection efficiency and enhanced adsorption capacity in a single porous probe remains a significant challenge. In this study, we successfully synthesized a two-dimensional imine-based TAP-COF using 2,4,6-triformylphloroglucinol and tri(4-aminophenyl)amine as raw materials. TAP-COF exhibited excellent properties, including a large specific surface area of 685.65 m2·g-1, exceptional thermal stability (>440 °C), chemical stability, temporal stability, and recyclability. Fluorescence testing revealed that TAP-COF exhibited remarkable specificity and high sensitivity for detecting Cu2+. The fluorescence mechanism, in which the excited state intramolecular proton transfer was impeded by the interaction of Cu2+ with C═O and C-N bonds on TAP-COF upon the addition of Cu2+, was further elucidated through experimental and theoretical methods. Furthermore, the adsorption capacity of TAP-COF toward Cu2+ was investigated, confirming the excellence of TAP-COF as a fluorescent probe and adsorbent for the specific detection and removal of Cu2+. This work holds significant implications for improving environmental and human health concerns associated with Cu2+ contamination.

Recent Developments in Colorimetric and Fluorometric Detection Methods of Trivalent Metal Cations (Al3+, Fe3+ and Cr3+) Using Schiff Base Probes: At a Glance

This review basically concerned with the application of different Schiff bases (SB) based fluorimetric (turn-off and turn-on) and colorimetric chemosensors for the detection of heavy metal cations particularly Al(III), Fe(III), and Cr(III) ions. Chemosensors based on Schiff bases have exhibited outstanding performance in the detection of different metal cations due to their facile and in-expensive synthesis, and their excellent coordination ability with almost all metal cations and stabilize them in different oxidation states. Moreover, Schiff bases have also been used as antifungal, anticancer, analgesic, anti-inflammatory, antibacterial, antiviral, antioxidant, and antimalarial etc. The Schiff base also can be used as an intermediate for the formation of various heterocyclic compounds. In this review, we have focused on the research work performed on the development of chemosensors (colorimetric and fluorometric) for rapid detection of trivalent metal cations particularly Al(III), Fe(III), and Cr(III) ions using Schiff base as a ligand during 2020-2022.

Label free electrochemical sensors for Pb(II) detection based on hemicellulose extracted from Opuntia Ficus Indica cactus

We aim to develop an electrochemical sensor for a divalent metal ion (lead II), a highly toxic water contaminant. We explore a sensor formed with a hemicellulose polysaccharide extracted from the Opuntia Ficus Indica cactus associated with agarose as a sensitive layer deposited on a gold electrode. This sensor combines the functional groups of hemicellulose that could form a complex with metal ions and agarose with gelling properties to form a stable membrane. The sensor demonstrated a loading ability of Pb2+, with higher affinity compared to other metal ions such as Hg2+, Ni2+, and Cu2+, thanks to the chemical structure of hemicellulose. The detection was measured by square wave voltammetry based on a well-defined redox peak of the metal ions. The sensor shows high sensitivity towards Pb2+ with a detection limit of 1.3 fM. The application in river and sea water using the standard addition method for lead detection was studied.

Photo-assisted "co-movement catalysis": CoFe2O4/CNS heterojunction based portable electrochemical sensor for simultaneous detection of Pb2+ and Cd2+ in natural water

Heavy metal ions (HMIs) seriously threaten human health even under trace conditions. Therefore, accurate, efficient and simultaneous detection of multiple HMIs is of great significance. Here, a strategy of "co-movement catalysis" based on photo-assisted electrochemical catalysis is proposed by constructing a flexible electrochemical sensor with CoFe2O4/CNS heterojunction-modified nickel foam as the working electrode for simultaneous detection of HMIs. Regarding photo-assisted catalysis, CoFe2O4/CNS nanocomposites formed a p-n type heterojunction, effectively separating photo-generated electron-hole pairs and reducing photo-generated carriers' recombination rate, leading to the catalytic reaction of photogenerated electrons and holes with HMIs and atoms to improve the efficiency of preconcentration and stripping, further amplifying the electrochemical signal. Regarding electrochemical catalysis, the CoFe2O4 spinel contains variable valence transition metal ions Fe2+/Fe3+ and Co2+/Co3+, which can reduce and oxidize HMIs circularly, further enhancing the sensor's sensitivity. The portable sensor based on "co-movement catalysis" exhibited sensitive detection performance. The linear range is 0.100-10.0 μM for Pb2+ and 1.00-10.0 μM for Cd2+, with the detection limit of 0.0310 μM for Pb2+ and 0.219 μM for Cd2+, respectively. The recovery rate of the sensor to natural water samples is between 96% and 105%, which proves its development potential in environmental monitoring.

In-situ growth of porous rod-like tungsten oxide for electrochemical determination of cupric ion

Preconcentration can effectively enhance the detection performance of electrodes in the electrochemical detection of heavy metal ions, but it also presents challenges for real-time monitoring. Several attempts have been made to optimize preconcentration by improving the adsorption capacity or detection mechanism of the electrode. The valence transfer of tungsten oxide between W5+/W6+ can participate in the reduction between the electrode material and heavy metal ions, playing a role in preconcentration to some extent. Therefore, we developed a WO3/SSM electrochemical sensor for the detection of Cu(II) that utilizes the valence variation property of WO3. The crystallinity and microstructure of the WO3/SSM electrode can be regulated by controlling the deposition parameters, and we prepared three types of WO3/SSM with different morphologies to identify the influence of the electrochemical effective surface area. The proposed electrode shows high performance as a Cu(II) sensor under short preconcentration time (60 s), with an excellent sensitivity of 14.113 μA μM-1 cm-2 for 0.1-10.0 μM and 4.7356 μA μM-1 cm-2 for 10.0-20.0 μM. Overall, the combined effect of morphology and valence transfers shortens the preconcentration time and optimizes preconcentration while ensuring excellent electrode performance. This WO3/SSM electrode is expected to drive great advances in the application of tungsten oxide in the electrochemical detection of heavy metal ions.

Immobilization-free electrochemical homogeneous aptasensor for highly sensitive detection of carcinoembryonic antigen by dual amplification strategy

Electrochemical aptasensor has been widely studied, while its practical application is limited by the unavoidable variations of aptamer loading densities and low signal amplification efficiency. To overcome these restrictions, an immobilization-free and label-free electrochemical homogeneous aptasensor was constructed for carcinoembryonic antigen (CEA) assay by combining RecJ_f exonuclease-mediated target cycling strategy and rolling circle amplification technology. In this system, the pre-immobilization of aptamers or other relevant signal elements on the electrode substrate is no longer necessary, thus the electrochemical homogeneous aptasensor shows good versatility on different transducers. Moreover, the whole recognition and signal amplification process are activated instantaneously by a non-professional operation of the solution mixture. This strategy can not only increase the stability (95.1% after 30 days of storage) and reproducibility (2.12% among five independent electrodes), but also further improve the sensitivity (detection limit of fg mL^-1 level) due to the free target recognition and dual signal amplification in the homogeneous solution phase. The proposed immobilization-free electrochemical homogeneous aptasensors on different electrode substrates both achieve satisfactory results in actual sample tests, which has the potential for commercial applications and the establishment of other target platforms in the future.

Modification of electrodes with polymer nanocomposites: Application to the simultaneous determination of Zn(II), Cd(II), and Cu(II) in water samples

Currently, there is a need for fast and sensitive analytical methods for monitoring metals in water due to the progressive increase in the presence of metal ions in the environment. These metals reach the environment mainly from industrial activity and heavy metals are non-biodegradable. The present work evaluates different polymeric nanocomposites to carry out the simultaneous electrochemical determination of Cu, Cd, and Zn in water samples. Screen-printed carbon electrodes (SPCE) were modified with the nanocomposites, which were obtained by a mixture of graphene, graphite oxide, and polymers, such as polyethyleneimide, gelatin, and chitosan. These polymers have amino groups in their matrix, giving the nanocomposite the ability to retain divalent cations. However, the availability of these groups plays a fundamental role in the retention of these metals. The modified SPCEs were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrode that presented the best performance was selected to determine the concentration of metal ions in water samples by square-wave anodic stripping voltammetry. The obtained detection limits were 0.23 μg L^-1, 0.53 μg L^-1, and 1.52 μg L^-1 for Zn(II), Cd(II), and Cu(II), respectively, with a lineal range of 0.1-50 μg L^-1. The obtained results made it possible to conclude that the method developed using the SPCE modified with the polymeric nanocomposite presented adequate LODs, reasonable sensitivity, selectivity, and reproducibility. Besides, this platform is an excellent tool for developing devices to simultaneously determine heavy metals in environmental samples.

Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 μg L-1 and 0.6 μg L-1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals.

Microfluidic Devices for Heavy Metal Ions Detection: A Review

The contamination of air, water and soil by heavy metal ions is one of the most serious problems plaguing the environment. These metal ions are characterized by a low biodegradability and high chemical stability and can affect humans and animals, causing severe diseases. In addition to the typical analysis methods, i.e., liquid chromatography (LC) or spectrometric methods (i.e., atomic absorption spectroscopy, AAS), there is a need for the development of inexpensive, easy-to-use, sensitive and portable devices for the detection of heavy metal ions at the point of interest. To this direction, microfluidic and lab-on-chip (LOC) devices fabricated with novel materials and scalable microfabrication methods have been proposed as a promising approach to realize such systems. This review focuses on the recent advances of such devices used for the detection of the most important toxic metal ions, namely, lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd) and chromium (Cr) ions. Particular emphasis is given to the materials, the fabrication methods and the detection methods proposed for the realization of such devices in order to provide a complete overview of the existing technology advances as well as the limitations and the challenges that should be addressed in order to improve the commercial uptake of microfluidic and LOC devices in environmental monitoring applications.

New Prospects in the Electroanalysis of Heavy Metal Ions (Cd, Pb, Zn, Cu): Development and Application of Novel Electrode Surfaces

The detection of toxic heavy metal ions, especially cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu), is a global problem due to ongoing pollution incidents and continuous anthropogenic and industrial activities. Therefore, it is important to develop effective detection techniques to determine the levels of pollution from heavy metal ions in various media. Electrochemical techniques, more specifically voltammetry, due to its properties, is a promising method for the simultaneous detection of heavy metal ions. This review examines the current trends related to electrode formation and analysis techniques used. In addition, there is a reference to advanced detection methods based on the nanoparticles that have been developed so far, as well as formation with bismuth and the emerging technique of screen-printed electrodes. Finally, the advantages of using these methods are highlighted, while a discussion is presented on the benefits arising from nanotechnology, as it gives researchers new ideas for integrating these technologies into devices that can be used anywhere at any time. Reference is also made to the speciation of metals and how it affects their toxicity, as it is an important subject of research.

Simple colorimetric copper(II) sensor - Spectral characterization and possible applications

New o-hydroxyazocompound L bearing pyrrole residue was obtained in the simple synthetic protocol. The structure of L was confirmed and analyzed by X-ray diffraction. It was found that new chemosensor can be successfully used as copper(II) selective spectrophotometric regent in solution and can be also applied for the preparation of sensing materials generating selective color signal upon interaction with copper(II). Selective colorimetric response towards copper(II) is manifested by a distinct color change from yellow to pink. Proposed systems were effectively used for copper(II) determination at concentration level 10^-8 M in model and real samples of water.

A sensitive electrochemical sensor based on 3D porous melamine-doped rGO/MXene composite aerogel for the detection of heavy metal ions in the environment

Herein, we developed a unique screen-printed carbon electrode (SPCE) with three-dimensional melamine-doped graphene oxide/MXene composite aerogel (3D MGMA) modification, which is used for the simultaneous and sensitive detection of three metal ions (Zn²⁺, Cd²⁺, and Pb²⁺) in the environment. A self-assembly method was used to fabricate 3D MXene aerogels based on MXene, graphene oxide (GO), and melamine. Notably, the network-like 3D structure combining 2D MXene and rGO sheets can provide a high ratio of surface area and enriched functional clusters, which are beneficial for improving the electrical conductivity and promoting the uptake of heavy metal ions. In the linear range of 3-900 μg L^-1, the constructed innovative sensing platform can sensitively detect Zn²⁺, Cd²⁺, and Pb²⁺ simultaneously, with detection limits of 0.48 μg L^-1,0.45 μg L^-1 and 0.29 μg L^-1 respectively. This work reflects precision and reliability in the detection of three water samples (tap water, Minzhu lake and Yangtze River) and four cereal samples (sorghum, rice, wheat and corn), proposing a novel strategy for monitoring heavy metal ions in the natural environment.

The Role of Silver Nanoparticles in Electrochemical Sensors for Aquatic Environmental Analysis

With rapidly increasing environmental pollution, there is an urgent need for the development of fast, low-cost, and effective sensing devices for the detection of various organic and inorganic substances. Silver nanoparticles (AgNPs) are well known for their superior optoelectronic and physicochemical properties, and have, therefore, attracted a great deal of interest in the sensor arena. The introduction of AgNPs onto the surface of two-dimensional (2D) structures, incorporation into conductive polymers, or within three-dimensional (3D) nanohybrid architectures is a common strategy to fabricate novel platforms with improved chemical and physical properties for analyte sensing. In the first section of this review, the main wet chemical reduction approaches for the successful synthesis of functional AgNPs for electrochemical sensing applications are discussed. Then, a brief section on the sensing principles of voltammetric and amperometric sensors is given. The current utilization of silver nanoparticles and silver-based composite nanomaterials for the fabrication of voltammetric and amperometric sensors as novel platforms for the detection of environmental pollutants in water matrices is summarized. Finally, the current challenges and future directions for the nanosilver-based electrochemical sensing of environmental pollutants are outlined.

Functionalization of Screen-Printed Electrodes with Grape Stalk Waste Extract-Assisted Synthesized Silver and Gold Nanoparticles: Perspectives of Electrocatalytically Enhanced Determination of Uranyl Ion and Other Heavy Metals Ions

Recently, nanotechnology and nanoparticles (NPs) such as AgNPs and AuNPs have become important in analytical chemistry due to their great potential to improve the performance of electrochemical sensors. In this work, Ag and Au nanoparticles have been synthesized using a green route in which a grape stalk waste extract is used as a reducing agent to obtain metallic nanoparticles. These NPs were used to customize the surface of commercial screen-printed electrodes (SPCNFEs). The spin-coating method was used to modify commercial SPCNFEs under a nitrogen atmosphere. The resulting electrodes were used in a determination study of Cd(II), Pb(II), and U(VI) with differential pulse anodic stripping voltammetry (DPASV). The customized green AgNPs and AuNPs electrodes presented higher sensitivity and electroanalytical performance than the non-modified SPCNFE. The results showed that the best analytical parameters were obtained with the green, silver nanoparticle SPCNFEs, with a LOD of 0.12 μg L^-1 for Pb(II), which is a lower value compared to the most restrictive regulation guidelines. Additionally, the U(VI) ion was successfully determined using the developed G-AgNPs-SPCNFE in spiked tap water, showing comparable results with the ICP-MS technique.

Novel sensor array distinguishes heavy metal ions based on multiple fluorescence channels from dendritic mesoporous silica nanoparticles

In this work, we demonstrated a sensor array with multiple fluorescence channels using dendritic mesoporous silica nanoparticles embedded with three quantum dots for the determination of four heavy metal ions (Hg²⁺, Cu²⁺, Cr³⁺, and Ag⁺). Carboxyl-modified CdTe QDs with three different fluorescence emission wavelengths were loaded onto a dendritic mesoporous supporter by an amidation reaction. The fluorescence sensor array exhibited excellent analytical performance for discrimination and semi-quantification of heavy metal ions from a single test, which simplified detection procedures. The four heavy metal ions exhibited different degrees of quenching of the fluorescence emission intensities of the three quantum dots and resulted in a variant data matrix for linear discriminant analysis. Under optimized conditions, the fluorescence sensor array discriminated the four heavy metal ions in a concentration range of 0.05-5 μmol/L, and semi-quantified Hg²⁺, Cu²⁺, Cr³⁺, and Ag⁺ with a limit of detection of 2.51 nmol/L, 5.15 nmol/L, 3.81 nmol/L, and 5.74 nmol/L, respectively. The fluorescence sensor array integrated the sensing units into a single nanoparticle instead of the complex multiple detection steps used in traditional sensor arrays, providing an alternative strategy for constructing a single-well sensing platform. Furthermore, the fluorescence sensor array showed great practical potential for distinguishing heavy metal ions in raw water and crayfish samples.

Low-pressure ultraviolet-H2O2 photolysis for restoring the anodic stripping voltammetry signal: a new strategy for the detection of heavy metal ions in complex organic matter

A new strategy based on low-pressure ultraviolet (LPUV)-H₂O₂ advanced oxidation photolysis for the quantitative determination of organic heavy metal ions (HMIs) in soil was proposed for the efficient, low-cost, accurate, and green detection of Pb(II) and Cd(II) in soil extracts by breaking the complexation of HMIs and organic matters, consequently restoring the ASV signals of target HMIs. The key parameters of the proposed LPUV-H₂O₂ photolysis system for the restoration of stripping responses were optimized; the conversion of organic matter to inorganic matter during the photolysis was investigated by total organic carbon (TOC); the degradation kinetics of humic acid sodium (HAS) was measured by UV-vis spectroscopy (UV); the pathway of HAS converted to small molecule organics during degradation was observed by fluorescence spectroscopy (FS); additionally, Fourier transform infrared spectroscopy (FTIR) was used to study the complexation between HAS and HMIs. The results showed that the stripping signals of target HMIs in the simulated soil samples can be restored to nearly 100% with a good repeatability, and the restoration ratio of the stripping signal fluctuated within 10%. And the feasibility of the proposed method for the accurate detection of HMIs in the real soil samples was verified; the results showed that 93.7% of Cd(II) and 92.5% of Pb(II) in real soil extracts were detectable.

Microbial fuel cell: A green eco-friendly agent for tannery wastewater treatment and simultaneous bioelectricity/power generation

This review paper emphasised on the origin of hexavalent chromium toxicity in tannery wastewater and its remediation using novel Microbial Fuel Cell (MFC) technology, including electroactive bacteria, which are known as exoelectrogens, to simultaneously treat wastewater and its action in the production of bioenergy and the mechanism of Cr⁶⁺ reduction. Also, there are various parameters like electrode, pH, mode of operation, time of operation, and type of exchange membrane used for promising results shown in enhancing MFC production and remediation of Cr⁶⁺. Destructive anthropological activities, such as leather making and electroplating industries are key sources of hexavalent chromium contamination in aquatic repositories. When Cr⁶⁺ enters the food chain and enters the human body, it has the potential to cause cancer. MFC is a green innovation that generates energy economically through the reduction of toxic Cr⁶⁺ to less toxic Cr³⁺. The organic substrates utilized at the anode of MFC act as electrons (e^-) donors. This review also highlighted the utilization of cheap substrates to make MFCs more economically suitable and the energy production at minimum cost.

Simultaneous Quantitation of Lead and Cadmium on an EDTA-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Cadmium (Cd) and lead (Pb) are classified as category one toxicants. The provisional guideline values, according to the World Health Organization (WHO), for Cd and Pb are 3 and 10 ppb, respectively. An easy, quick, and cheap analytical technique is in demand for the determination of these toxic heavy metals in water. Hence, a novel electrochemical sensing platform is developed by modifying the glassy carbon electrode with ethylenediaminetetraacetic acid (EDTA)-functionalized reduced graphene oxide (ErGO) for the low-cost simultaneous quantitation of toxic heavy-metal ions, lead and cadmium, in real water samples. EDTA is grafted to the surface of graphene oxide, via amine linkage, and the oxygen functionality is reduced by a green agent, tyrosine. Various physical and electrochemical characterizations of the as-prepared electrocatalytic material were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), ζ-potential, ultraviolet diffuse reflectance spectroscopy (UV-DRS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. The glassy carbon electrode (GCE) is modified with ErGO by a simple drop-casting method for simultaneous metal-ion quantitation by differential pulse voltammetry (DPV). EDTA functionalization of graphene oxide and its further reduction using the green agent enhance the stability and sensitivity of the electrode substrate. The limits of detection for cadmium and lead ions calculated for ErGO/GCE are 1.02 and 2.52 ppb, while the limits of quantification for lead and cadmium ions are 3.41 and 8.4 ppb, and their sensitivities are 0.8 and 0.6 nA/ppb, respectively. Real river water contains 200.2 ± 0.38 ppb of Pb²⁺ ions (mean ± stdev, n = 3) by the DPV technique, which is validated by ICP-OES analysis.

Carbon Nanomaterials-Based Electrochemical Sensors for Heavy Metal Detection

Heavy metals are commonly found in a wide range of environmental settings metals, but the potential toxicity associated with heavy metal exposure represents a major threat to global public health. It is thus vital that approaches to efficiently, reliably, and effectively detecting heavy metals in a range of sample types be established. Carbon nanomaterials offer many advantageous properties that make them well-suited to the design of sensitive, selective, easy-to-operate electrochemical biosensors ideal for detecting heavy metal ions. The present review offers an overview of recent progress in the development of carbon nanomaterial-based electrochemical sensors used to detect heavy metals. In addition to providing a detailed discussion of certain carbon nanomaterials such as carbon nanotubes, graphene, carbon fibers, carbon quantum dots, carbon nanospheres, mesoporous carbon, and Graphdiyne, we survey the challenges and future directions for this field. Overall, the studies discussed herein suggest that the further development of carbon nanomaterial-modified electrochemical sensors will support the integration of increasingly advanced sensor platforms to aid in detecting heavy metals in foods, environmental samples, and other settings, thereby benefitting human health and society as a whole.