Electrochemical sensing of heavy metal ions with inorganic, organic and bio-materials

Flexible electronics for heavy metal ion detection in water: a comprehensive review

Flexible electronics offer a versatile, rapid, cost-effective and portable solution to monitor water contamination, which poses serious threat to the environment and human health. This review paper presents a comprehensive exploration of the versatile platforms of flexible electronics in the context of heavy metal ion detection in water systems. The review overviews of the fundamental principles of heavy metal ion detection, surveys the state-of-the-art materials and fabrication techniques for flexible sensors, analyses key performance metrics and limitations, and discusses future opportunities and challenges. By highlighting recent advances in nanomaterials, polymers, wireless integration, and sustainability, this review aims to serve as an essential resource for researchers, engineers, and policy makers seeking to address the critical challenge of heavy metal contamination in water resources. The versatile promise of flexible electronics is thoroughly elucidated to inspire continued innovation in this emerging technology arena.

Electrochemical Sensors for Heavy Metal Ion Detection in Aqueous Medium: A Systematic Review

Heavy metal ions (HMIs) are very harmful to the ecosystem when they are present in excess of the recommended limits. They are carcinogenic in nature and can cause serious health issues. So, it is important to detect the metal ions quickly and accurately. The metal ions arsenic (As3+), cadmium (Cd2+), chromium (Cr3+), lead (Pb2+), and mercury (Hg2+) are considered to be very toxic among other metal ions. Standard analytical methods like atomic absorption spectroscopy, atomic fluorescence spectroscopy, and X-ray fluorescence spectroscopy are used to detect HMIs. But these methods necessitate highly technical equipment and lengthy procedures with skilled personnel. So, electrochemical sensing methods are considered to be more advantageous because of their quick analysis with precision and simplicity to operate. They can detect a wide range of heavy metals providing real-time monitoring and are cost-effective and enable multiparametric detection. Various sensing applications necessitate severe regulation regarding the modification of electrode surfaces. Numerous nanomaterials such as graphene, carbon nanotubes, and metal nanoparticles have been extensively explored as interface materials in electrode modifiers. These nanoparticles offer excellent electrical conductivity, distinctive catalytic properties, and high surface area resulting in enhanced electrochemical performance. This review examines different HMI detection methods in an aqueous medium by an electrochemical sensing approach and studies the recent developments in interface materials for altering the electrodes.

Mg/S@g-C3N4 nanosheets: A promising fluorescence sensor for selective Cu2+ detection in water

This work describes the development of a novel fluorescence sensor based on magnesium/S@g-C3N4 nanosheets for selective detection of copper (Cu2+) ions in water. Mg/S@g-C3N4 nanosheets were prepared by the polycondensation technique and investigated by X-ray diffraction (XRD), ATR-FTIR spectroscopy, scanning electron microscopy (SEM), surface area (BET), and UV-Vis optical absorption measurements. XRD and ATR-FTIR analysis showed the characteristic peaks for S@g-C3N4. The broad full width at half maximum (0.056 radians) implies a smaller crystallite size, representing smaller Mg/S@g-C3N4 sheets. SEM micrograph showed non-exfoliated nanosheets with flake-like structures. The EDS mapping confirmed the presence of magnesium, carbon, nitrogen, and sulfur throughout the nanosheets. The Mg/S@g-C3N4 nanosheets possess a high surface area of 40 m2/g and mesopores within the nanosheets, with a size of 1.57 nm. The band gap of the Mg/S@g-C3N4 nanosheet was estimated to be 3.0 eV. The sensor exhibits a strong quenching response towards Cu2+ ions, with a decrease in fluorescence intensity as the concentration of Cu2+ increased from 1 μM to 20 μM. The Stern-Volmer quenching constant (KSV) showed a relatively high value of 185053 M-1. The estimated value of LOD by the Mg/S@g-C3N4 sensor for Cu2+ was 16.2 nM. The sensor offered high sensitivity and selectivity for Cu2+ detection over other heavy metals.

Cytosine-Rich Oligonucleotide and Electrochemically Reduced Graphene Oxide Nanocomposite for Ultrasensitive Electrochemical Ag+ Sensing

Silver ions (Ag+) are crucial in various fields, but pose environmental and health risks at high concentrations. This study presents a straightforward approach for the ultra-trace detection of Ag+, utilizing a composite of a cytosine-rich oligonucleotide (CRO) and an electrochemically reduced graphene oxide (ERGO). Initially, ERGO was synthesized on a glassy carbon electrode (GCE) through the reduction of graphene oxide (GO) via cyclic voltammetry. A methylene blue-tagged CRO (MB-CRO) was then anchored to the ERGO surface through π-π interactions, resulting in the formation of an MB-CRO-modified ERGO electrode (MB-CRO/ERGO-GCE). The interaction with Ag+ ions induced the formation of silver-mediated C-Ag+-C coordination, prompting the MB-CRO to adopt a hairpin structure. This conformational change led to the desorption of the MB-CRO from the ERGO-GCE, causing a variation in the redox current of the methylene blue associated with the MB-CRO. Electrochemical assays revealed that the sensor exhibits extraordinary sensitivity to Ag+ ions, with a linear detection range from 1 femtomolar (fM) to 100 nanomolars (nM) and a detection limit of 0.83 fM. Moreover, the sensor demonstrated high selectivity for Ag+ ions and several other benefits, including stability, reproducibility, and straightforward fabrication and operational procedures. Additionally, real sample analyses were performed using the modified electrode to detect Ag+ in tap and pond water samples, yielding satisfactory recovery rates.

Trace detection of cadmium (II) ions based on an excessively tilted fiber grating

Cadmium (Cd2+) ion is one of the most crucial industrial pollutants that cause serious harm to the human body. We proposed and experimentally demonstrated a highly sensitive Cd2+ sensor based on hydrogel coated excessively tilted fiber grating. The hydrogel with the functional monomer of the allyl thiourea can specifically bind to Cd2+, and hence forming a complex. The grating excites high order cladding modes, and ensures a sufficient interaction between the light and hydrogel binding to Cd2+, providing highly sensitive monitoring. The results show that the sensor can detect 0-160 pM Cd2+ in aqueous solution. The maximum sensitivity is 10600 nm/µM, and the minimum detection concentration is 20 pM (about 0.004 ppb), which is much less than that of the international standard (3 ppb). The proposed sensor exhibits high sensitivity, ultra-low detection limit, specificity, and a compact structure, offering potential as a tool for Cd2+ detection in aqueous solution.

Simultaneous Electrochemical Detection of Cu2+ and Zn2+ in Pig Farm Wastewater

In recent years, the rapid development of pig farming has led to a large quantity of heavy metal-polluted wastewater. Thus, it was desirable to develop a simple heavy metal detection method for fast monitoring of the wastewater from the pig farms. Therefore, there was an urgent need to develop a simple method for rapidly detecting heavy metal ions in pig farm wastewater. Herein, a simple electrochemical method for simultaneous detection of Cu2+ and Zn2+ was developed and applied to pig farm wastewater. With a glassy carbon electrode and anodic stripping voltammetry, simultaneous detection of Cu2+ and Zn2+ in water was achieved without the need for complicated electrode modification. Furthermore, it was found that the addition of Cd2+ can enhance the response current of the electrode to Zn2+, which increased the signal by eight times. After systematic optimization, the limit of detection (LOD) of 9.3 μg/L for Cu2+ and 45.3 μg/L for Zn2+ was obtained. Finally, it was successfully applied for the quantification of Cu2+ and Zn2+ with high accuracy in pig farm wastewater. This work provided a new and simple solution for fast monitoring of the wastewater from pig farms and demonstrated the potential of electrochemical measurement for application in modern animal husbandry.

The Synthesis of FeS and Investigation on Electrochemical Sensing Toward Neuroprotector

Background Electrochemical sensing is a versatile field that uses electrochemistry concepts to detect and measure various substances. It finds applications in clinical diagnostics and environmental monitoring. Scientists are currently working on creating reliable electrochemical sensing devices that can accurately detect ascorbic acid. Iron sulfide (FeS) has emerged as a promising material for these sensors due to its excellent electrical conductivity, catalytic activity, and stability.  Materials and methods The FeS nanoparticles were synthesized through the hydrothermal method of synthesis. The glassy carbon electrode (GCE) with a surface area of 0.071 cm2 was modified with FeS before the working electrode was mechanically polished with 1 µm, 0.3 µm, and 0.05 µm alumina pastes for mirror finishing. Then it was subjected to ultrasonication in double distilled water for a few minutes to clean the surface of GCE. The FeS suspension was prepared by dispersing 5 mg of FeS in 10 mL of ethanol during 20 minutes of ultrasonic agitation then the GCE was coated with 10 μL of the suspension by drop coating method and dried in air. Results In this study, FeS nanoparticles were synthesized by the hydrothermal method of synthesis, and it was tested for their electrochemical sensing properties by various tests. Based on the field emission-scanning electron microscope (FE-SEM) analysis, scan rate effect test, cyclic voltammetric test, X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) spectroscopy analysis done and results obtained, it was seen that the synthesized FeS nanoparticles are highly pure and have a crystalline structure. FeS has an even morphology. The synthesized particles also showed highly sensitive and specific sensing toward ascorbic acid when compared to unmodified 10.1 µA electrodes with a sensing value of 12.51 μA, thereby fulfilling the aim of this study. Conclusion Based on the outcomes of the diverse tests carried out, it is evident that the sample displayed a high crystalline nature as indicated by the XRD test. Additionally, the sample exhibited a uniform morphology, exceptional stability, and remarkable sensitivity. The developed FeS-based electrochemical sensor was found to be exceptionally pure and showed excellent performance, showcasing both high sensitivity and selectivity toward ascorbic acid.

A comprehensive review on enzyme-based biosensors: Advanced analysis and emerging applications in nanomaterial-enzyme linkage

Biosensors with nanomaterials and enzymes detect and quantify specific targets in samples, converting recognition into measurable signals. The study explores the intrinsic synergy between these elements for detecting and quantifying particular targets in biological and environmental samples, with results demonstrated through bibliometric analysis and a comprehensive review of enzyme-based biosensors. Using WoS, 57,331 articles were analyzed and refined to 880. Key journals, countries, institutions, and relevant authors were identified. The main areas highlighted the multidisciplinary nature of the field, and critical keywords identified five thematic clusters, revealing the primary nanoparticles used (CNTs, graphene, AuNPs), major application fields, basic application themes, and niche topics such as sensitive detection, peroxidase activity, and quantum dot utilization. The biosensor overview covered nanomaterials and their primary applications, addressing recent advances and inherent challenges. Patent analysis emphasized the U.S. leadership in the industrial sector, contrasting with China's academic prominence. Future studies should focus on enhancing biosensor portability and analysis speed, with challenges encompassing efficient integration with recent technologies and improving stability and reproducibility in the nanomaterial-enzyme interaction.

Copper-zinc nanoparticle-decorated nitrogen-doped carbon composite for electrochemical determination of triclosan

A new sensor based on copper-zinc bimetal embedded and nitrogen-doped carbon-based composites (CuZn@NC) was prepared for triclosan (TCS) detection by pyrolyzing the precursor of Cu-Zn binuclear metal-organic framework (MOF). The performance for detecting TCS was evaluated using linear scanning voltammetry (LSV) and differential pulse voltammetry (DPV), and the proton and electron numbers during TCS oxidation have been proved to be one-to-one. The results indicated that CuZn@NC can present a satisfactory analysis performance for TCS detection. Under the optimized conditions, the linear response range was 0.2-600 µM and the detection limit was 47.9 nM. The sensor presented good stability (signal current dropped only 2.5% after 21 days) and good anti-interference of inorganic salts and small molecular organic acids. The good recovery (97.5-104.1%) for detecting spiked TCS in commercial products (toothpaste and hand sanitizer) suggested its potential for routine determination of TCS in real samples.

Nanomaterials based sensors for analysis of food safety

The freshnessof the food is a major issue because spoiled food lacks critical nutrients for growth and could be harmful to human health if consumed directly. Nanomaterials are captivating due to their unique properties like large surface area, high selectivity, small dimension, great biocompatibility and conductivity, real-time onsite analysis, etc. which give them an advantage over conventional evaluation techniques. Despite these advantages of nanomaterials used in food safety and their preservation, food products can still get affected by various environmental factors (like pH, temperature, etc.), making the use of time-temperature indicators more condescending. This review is a comprehensive study on food safety, its causes, the responsible analytes, their remedies by various nanomaterials, the development of various nanosensors, and the various challenges faced in maintaining food safety standards to reduce the risk of contaminants.

Organic Electronics in Biosensing: A Promising Frontier for Medical and Environmental Applications

The promising field of organic electronics has ushered in a new era of biosensing technology, thus offering a promising frontier for applications in both medical diagnostics and environmental monitoring. This review paper provides a comprehensive overview of organic electronics' remarkable progress and potential in biosensing applications. It explores the multifaceted aspects of organic materials and devices, thereby highlighting their unique advantages, such as flexibility, biocompatibility, and low-cost fabrication. The paper delves into the diverse range of biosensors enabled by organic electronics, including electrochemical, optical, piezoelectric, and thermal sensors, thus showcasing their versatility in detecting biomolecules, pathogens, and environmental pollutants. Furthermore, integrating organic biosensors into wearable devices and the Internet of Things (IoT) ecosystem is discussed, wherein they offer real-time, remote, and personalized monitoring solutions. The review also addresses the current challenges and future prospects of organic biosensing, thus emphasizing the potential for breakthroughs in personalized medicine, environmental sustainability, and the advancement of human health and well-being.

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.

Hybrid Nanoparticle/DNAzyme Electrochemical Biosensor for the Detection of Divalent Heavy Metal Ions and Cr3

A hybrid noble nanoparticle/DNAzyme electrochemical biosensor is proposed for the detection of Pb2+, Cd2+, and Cr3+. The sensor takes advantage of a well-studied material that is known for its selective interaction with heavy metal ions (i.e., DNAzymes), which is combined with metallic nanoparticles. The double-helix structure of DNAzymes is known to dissociate into smaller fragments in the presence of specific heavy metal ions; this results in a measurable change in device resistance due to the collapse of conductive inter-nanoparticle DNAzyme bridging. The paper discusses the effect of DNAzyme anchoring groups (i.e., thiol and amino functionalization groups) on device performance and reports on the successful detection of all three target ions in concentrations that are well below their maximum permitted levels in tap water. While the use of DNAzymes for the detection of lead in particular and, to some extent, cadmium has been studied extensively, this is one of the few reports on the successful detection of chromium (III) via a sensor incorporating DNAzymes. The sensor showed great potential for its future integration in autonomous and remote sensing systems due to its low power characteristics, simple and cost-effective fabrication, and easy automation and measurement.

Multiple fluorescence polymer dots-based differential array sensors for highly efficient heavy metal ions detection

Water pollution caused by harmful heavy metal ions (HMIs) can significantly impact aquatic ecosystems and pose a high risk to human health. In this work, equipped with ultra-high fluorescence brightness, efficient energy transfer, and environmentally friendly performance, polymer dots (Pdots) were employed to construct a pattern recognition fluorescent HMIs detection platform. A single-channel unary Pdots differential sensing array was first developed to identify multiple HMIs with 100% classification accuracy. Then an "all-in-one" multiple Förster resonance energy transfer (FRET) Pdots differential sensing platform was constructed to discriminate HMIs in the artificial polluted water samples and actual water samples, exhibiting high classification accuracy in distinguishing HMIs. The proposed strategy leverages the compounded cumulative differential variation of diverse sensing channels for analytes, which is anticipated to find extensive applications in other fields for detection purposes.

Application of Co3O4 nanocrystal/rGO for simultaneous electrochemical detection of cadmium and lead in environmental waters

Sensing of cadmium (Cd) and lead (Pb) in environmental samples is crucial for identifying potential health risks associated with exposure to these heavy metals as well as understanding the extent of heavy metal contamination in different environments and its impact on the ecosystem. The present study elucidates the development of a novel electrochemical sensor that can detect Cd (II) and Pb (II) ions simultaneously. This sensor is fabricated using reduced graphene oxide (rGO) and cobalt oxide nanocrystals (Co₃O₄ nanocrystals/rGO). The characterization of Co₃O₄ nanocrystals/rGO was done by using various analytical techniques. The incorporation of cobalt oxide nanocrystals with intense absorption properties results in an amplification of the electrochemical current generated on the surface of the sensor by heavy metals. This, when coupled with the unique properties of the GO layer, enables the identification of trace levels of Cd (II) and Pb (II) in the surrounding environment. The electrochemical testing parameters were meticulously optimized to obtain high sensitivity and selectivity. The Co₃O₄ nanocrystals/rGO sensor exhibited exceptional performance in detecting Cd (II) and Pb (II) within a concentration range of 0.1-450 ppb. Notably, the limits of detection (LOD) for Pb (II) and Cd (II) were found to be highly impressive at 0.034 ppb and 0.062 ppb, respectively. The Co₃O₄ nanocrystals/rGO sensor integrated with the SWASV method displayed notable resistance to interference and exhibited consistent reproducibility and stability. Therefore, the suggested sensor has the potential to serve as a technique for detecting both ions in aqueous samples using SWASV analysis.

Dual-mode biosensor platform based on synergistic effects of dual-functional hybrid nanomaterials

Detection of biomarkers is very vital in the prevention, diagnosis and treatment of diseases. However, due to the poor accuracy and sensitivity of the constructed biosensors, we are now facing great challenges. In addressing these problems, nanohybrid-based dual mode biosensors including optical-optical, optical-electrochemical and electrochemical-electrochemical have been developed to detect various biomarkers. Integrating the merits of nanomaterials with abundant active sites, synergy and excellent physicochemical properties, many bi-functional nanohybrids have been reasonable designed and controllable preparation, which applied to the construction dual mode biosensors. Despite the significant progress, further efforts are still needed to develop dual mode biosensors and ensure their practical application by using portable digital devices. Therefore, the present review summarizes an in-depth evaluation of the bi-functional nanohybrids assisted dual mode biosensing platform of biomarkers. We are hoping this review could inspire further concepts in developing novel dual mode biosensors for possible detection application.

Amino-Functionalized Hierarchical Porous Carbon Derived from Zeolitic Imidazolate Frameworks for Ultrasensitive Electrochemical Sensing of Heavy Metals in Water

Electrochemical sensing provides a feasible avenue to monitor heavy metal ions (HMIs) in water, whereas the construction of highly sensitive and selective sensors remains challenging. Herein, we fabricated a novel amino-functionalized hierarchical porous carbon by the template-engaged method using ZIF-8 as the precursor and polystyrene sphere as the template, followed by carbonization and controllable chemical grafting of amino groups for efficient electrochemical detection of HMIs in water. The amino-functionalized hierarchical porous carbon features an ultrathin carbon framework with a high graphitization degree, excellent conductivity, unique macro-, meso-, and microporous architecture, and rich amino groups. As a result, the sensor exhibits prominent electrochemical performance with significantly low limits of detection for individual HMIs (i.e., 0.93 nM for Pb²⁺, 2.9 nM for Cu²⁺, and 1.2 nM for Hg²⁺) and simultaneous detection of HMIs (i.e., 0.62 nM for Pb²⁺, 1.8 nM for Cu²⁺, and 0.85 nM for Hg²⁺), which are superior to most reported sensors in the literature. Moreover, the sensor displays excellent anti-interference ability, repeatability, and stability for HMI detection in actual water samples.

Simultaneous voltammetric sensing of Zn2+, Cd2+, and Pb2+ using an electrodeposited Bi-Sb nanocomposite modified carbon paste electrode

A sensor for detecting Zn²⁺, Cd²⁺, and Pb²⁺ ions simultaneously based on the square wave anodic stripping response at a bismuth antimony (Bi-Sb) nanocomposite electrode was developed. The electrode was prepared in situ by electrodepositing bismuth and antimony on the surface of a carbon-paste electrode (CPE) while also reducing the analyte metal ions. The structure and performance of the Bi-Sb/CPE electrode were studied using scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and cyclic voltammetry. Operational conditions including the concentration of Sb and Bi, the type of electrolyte, pH, and preconcentration conditions were optimized. The linear ranges were determined to be 5-200 μg L^-1 for Zn²⁺, 1-200 μg L^-1 for Cd²⁺, and 1-150 μg L^-1 for Pb²⁺ with the optimized parameters. The limits of detection were 1.46 μg L^-1, 0.27 μg L^-1, and 0.29 μg L^-1 for Zn²⁺, Cd²⁺, and Pb²⁺, respectively. Furthermore, the Bi-Sb/CPE sensor is capable of selective determination of the target metals in the presence of the common cationic and anionic interfering species (Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Co²⁺, Cl^-, SO₄ ^2- and HCO₃ ^-). Finally, the sensor was successfully applied to the simultaneous determination of Zn²⁺, Cd²⁺, and Pb²⁺ in a variety of real-world water samples.

Practical Strategy for Arsenic(III) Electroanalysis without Modifier in Natural Water: Triggered by Iron Group Ions in Solution

Significant progress has been made in nanomaterial-modified electrodes for highly efficient electroanalysis of arsenic(III) (As(III)). However, the modifiers prepared using some physical methods may easily fall off, and active sites are not uniform, causing the potential instability of the modified electrode. This work first reports a promising practical strategy without any modifiers via utilizing only soluble Fe³⁺ as a trigger to detect trace-level As(III) in natural water. This method reaches an actual detection limit of 1 ppb on bare glassy carbon electrodes and a sensitivity of 0.296 μA ppb^-1 with excellent stability. Kinetic simulations and experimental evidence confirm the codeposition mechanism that Fe³⁺ is preferentially deposited as Fe⁰, which are active sites to adsorb As(III) and H⁺ on the electrode surface. This facilitates the formation of AsH₃, which could further react with Fe²⁺ to produce more As⁰ and Fe⁰. Meanwhile, the produced Fe⁰ can also accelerate the efficient enrichment of As⁰. Remarkably, the proposed sensing mechanism is a general rule for the electroanalysis of As(III) that is triggered by iron group ions (Fe²⁺, Fe³⁺, Co²⁺, and Ni²⁺). The interference analysis of coexisting ions (Cu²⁺, Zn²⁺, Al³⁺, Hg²⁺, Cd²⁺, Pb²⁺, SO₄^2-, NO₃^-, Cl^-, and F^-) indicates that only Cu²⁺, Pb²⁺, and F^- showed inhibitory effects on As(III) due to the competition of active sites. Surprisingly, adding iron power effectively eliminates the interference of Cu²⁺ in natural water, achieving a higher sensitivity for 1-15 ppb As(III) (0.487 μA ppb^-1). This study provides effective solutions to overcome the potential instability of modified electrodes and offers a practical sensing platform for analyzing other heavy-metal anions.

Detection of copper ions in an aqueous solution by a dual-peak long period fiber grating functionalized with a polypyrrole-chitosan composite

A dual-peak long period fiber grating (DP-LPFG) sensor functionalized by polypyrrole-chitosan composite was proposed for sensitive detection of Cu²⁺ ions in aqueous solution. The nitrogen atom on the polypyrrole ring and the amino group on the chitosan chain in the complex matrix can chelate the Cu²⁺ ions. Thus, the refractive index of the overlay changed and further modulated the transmission spectrum of DP-LPFG. After special design, the double peaks can move in opposite directions with the increase of Cu²⁺ ion concentration, thereby greatly improving detection sensitivity. The linear sensitivity of the fabricated sensor was measured to be 9.12 and 2.14 nm/ppm (0.61 and 0.14 nm/µM) for concentrations of 0.1-0.5 (1.5 µM-7.5 µM) and 0.5-2 ppm (7.5 µM-30 µM), respectively. In addition, the Langmuir isothermal model was used to evaluate the overall response of the sensor to Cu²⁺ ions quantitatively, and the detection limit was determined to be 0.05 ppb (0.75 nM). This ingenious sensor offers a new solution for sensitive detection of heavy metal ions in environmental water.

FeOOH nanosheet assisted metal ion coordination with porphyrins for rapid detection and removal of cadmium ions in water

Excessive cadmium ions in water bodies pose a severe challenge to ecology and human health, and the development of cadmium metal ion sensors is imperative. Here, we showed a dual-signal sensor based on colorimetry and fluorescence that was self-assembled from FeOOH nanosheets and TMPyP4. This nanocomposite enabled quick, selective cadmium ion detection. The Soret band at 442 nm in the UV absorption spectrum represented the coordination of cadmium ions with FeOOH@TMPyP4, and the absorbance increased linearly with increasing cadmium ion concentration (R² = 0.989 and linear range: 0.5-10 μM). In the presence of FeOOH nanosheets, the coordination of cadmium ions with FeOOH@TMPyP4 took only 70 min, and the detection limit of cadmium ions was as low as 0.24 μM. In addition, Cd²⁺ could be effectively removed from the nanocomposite due to its easy separation from water. This research developed a simple and efficient approach for detecting and removing heavy metal ions from water bodies.

Facile Label-Free Electrochemical DNA Biosensor for Detection of Osteosarcoma-Related Survivin Gene

A sensitive and selective electrochemical deoxyribonucleic acid (DNA) biosensor was developed for the determination of a osteosarcoma-related survivin gene by using celestine blue (CB) as a label-free hybridization indicator. The proposed strategy adopted a facile and low-cost working electrode with no need for other substances for electrode or DNA functionalization. The interaction mode between CB and DNA was studied by electrochemical and spectroscopic approaches, illustrating that the possible mode was intercalation with a binding number of 2 and a binding constant β of 10^12.87. Moreover, the label-free electrochemical DNA biosensor exhibited a good linear relationship toward the target gene in a range from 1.00 nM to 50.00 nM with a detection limit as low as 0.046 nM using 3σ estimating system. This facile and low-cost electrochemical method realized the rapid detection and accurate quantification of the target sequence in complicated serum samples, endowing its promising potential in the diagnosis and monitoring of genetic diseases.

Thiacalix[4]arene-based complex with Co(II) ions as electrode modifier for simultaneous electrochemical determination of Cd(II), Pb(II), and Cu(II)

A complex [Co₄(TCTA)₂(H₂O)₈]∙10H₂O (Co-TCTA) based on thiacalix[4]arene derivative has been synthesized for the first time using the solvothermal method. The glassy carbon electrode (GCE) modified with Co-TCTA (Co-TCTA/GCE) could simultaneously determine Cd²⁺, Pb²⁺, and Cu²⁺ at around - 0.75 V, - 0.60 V, and - 0.10 V (vs. ref. Ag/AgCl) and had good stability, selectivity, and reproducibility with relative standard deviation (RSD) of 4.4% for Cd²⁺, 1.4% for Pb²⁺, and 5.4% for Cu²⁺. Co-TCTA/GCE showed wide linear range of 0.4-8.0 μM for Cd²⁺, 0.4-7.0 μM for Pb²⁺, and 0.6-6.0 μM for Cu²⁺ when three ions were determined simultaneously. The limits of detection (LODs) of Cd²⁺, Pb²⁺, and Cu²⁺ were 0.071 μM, 0.022 μM, and 0.021 μM, respectively. Moreover, the sensor was used to determine three ions in lake water sample with satisfactory recoveries of 93.6-93.8% for Cd²⁺, 93.8-103.3% for Pb²⁺ and 94.6-95.3% for Cu²⁺. The good adsorption capacity of Co-TCTA and Co(II)/Co(0) circular mechanism on the surface of the electrode were proposed to enhance the electrochemical signals. This work enriched the theoretical research on the complexes for the determination of heavy metal ions.

Cadmium Ions' Trace-Level Detection Using a Portable Fiber Optic-Surface Plasmon Resonance Sensor

Environmental pollution with cadmium (Cd) is a major concern worldwide, with prolonged exposure to this toxic heavy metal causing serious health problems, such as kidney damage, cancer, or cardiovascular diseases, only to mention a few. Herein, a gold-coated reflection-type fiber optic--surface plasmon resonance (Au-coated FO-SPR) sensor is manufactured and functionalized with (i) bovine serum albumin (BSA), (ii) chitosan, and (iii) polyaniline (PANI), respectively, for the sensitive detection of cadmium ions (Cd2+) in water. Then, the three sensor functionalization strategies are evaluated and compared one at a time. Out of these strategies, the BSA-functionalized FO-SPR sensor is found to be highly sensitive, exhibiting a limit of detection (LOD) for Cd2+ detection at nM level. Moreover, the presence of Cd2+ on the FO-SPR sensor surface was confirmed by the X-ray photoelectron spectroscopy (XPS) technique and also quantified consecutively for all the above-mentioned functionalization strategies. Hence, the BSA-functionalized FO-SPR sensor is sensitive, provides a rapid detection time, and is cheap and portable, with potential applicability for monitoring trace-level amounts of Cd within environmental or potable water.

Symmetrically Ion-Gated In-Plane Metal-Oxide Transistors for Highly Sensitive and Low-Voltage Driven Bioelectronics

To provide a unique opportunity for on-chip scaled bioelectronics, a symmetrically gated metal-oxide electric double layer transistor (EDLT) with ion-gel (IG) gate dielectric and simple in-plane Corbino electrode architecture is proposed. Using amorphous indium-gallium-zinc oxide (a-IGZO) semiconductor and IG dielectric layers, low-voltage driven EDLTs with high ionotronic effects can be realized. More importantly, in contrast to the conventional asymmetric rectangular EDLTs which can cause non-uniform potential variation in the active channel layer and eventually degrade the sensing performance, the new symmetrical in-plane type EDLTs achieve high and spatially uniform ion responsive behaviors. The symmetrically gated a-IGZO EDLTs exhibited a responsivity of 129.4% to 5 ppm mercury (Hg²⁺ ) ions which are approximately three times higher than that with conventional electrode structure (responsivity of 38.5%). To confirm the viability of the new device architectures and the findings, the detailed mechanism of the symmetric gating effects in the in-plane EDLTs with a variety of electrical characterization and 3D fine element analysis simulations is also discussed.

Fluorescent indicators for live-cell and in vitro detection of inorganic cadmium dynamics

Cadmium contamination is a severe threat to the environment and food safety. Thus, there is an urgent need to develop highly sensitive and selective cadmium detection tools. The engineered fluorescent indicator is a powerful tool for the rapid detection of inorganic cadmium in the environment. In this study, the development of yellow fluorescent indicators of cadmium chloride by inserting a fluorescent protein at different positions of the high cadmium-specific repressor and optimizing the flexible linker between the connection points is reported. These indicators provide a fast, sensitive, specific, high dynamic range, and real-time readout of cadmium ion dynamics in solution. The excitation and emission wavelength of this indicator used in this work are 420/485 and 528 nm, respectively. Fluorescent indicators N0C0/N1C1 showed a linear response to cadmium concentration within the range from 10/30 to 50/100 nM and with a detection limit of 10/33 nM under optimal condition. Escherichia coli cells containing the indicator were used to further study the response of cadmium ion concentration in living cells. E. coli N1C1 could respond to different concentrations of cadmium ions. This study provides a rapid and straightforward method for cadmium ion detection in vitro and the potential for biological imaging.

Optical Detection of Copper Ions via Structural Dissociation of Plasmonic Sugar Nanoprobes

Heavy metal ions are known to cause environmental pollution and several human diseases because of their inherent toxicity. Among them, Cu²⁺ is an essential element for the human body, but its continuous exposure and accumulation may cause adverse effects. Thus, copper ion levels in aquatic environments are strictly regulated by international standards. Herein, we demonstrate a simple optical method for detecting Cu²⁺ using plasmonic sugar nanoprobes (PSNs) composed of gold nanoparticles and polysaccharides. Gold precursors were reduced to nanoparticles and spontaneously embedded in the sugar-based polymeric network with the sulfated residues of carrageenan during the polymerization procedure. Owing to the abundant functional residues of PSNs and their affinity toward Cu²⁺, we observed the Cu²⁺-mediated preferential dissociation of the PSNs, resulting in absorbance spectral shifts and scattering shifts of the PSNs. Based on these plasmon band shifts, Cu²⁺ below the EPA regulation level of 20 μM can be easily detected by the optimized experimental condition. Additionally, the reaction mechanism between the PSNs and Cu²⁺ was elucidated by indepth spectroscopic analyses, which revealed that the increased binding of Cu²⁺ to the sulfate groups in the PSNs induces the eventual decomposition of the PSNs.

A dual chamber microbial fuel cell based biosensor for monitoring copper and arsenic in municipal wastewater

This study investigated a dual-chamber microbial fuel cell-based biosensor (DC-MFC-B) for monitoring copper and arsenic in municipal wastewater. Operational conditions, including pH, flow rate, a load of organic substrate and external resistance load, were optimized to improve the biosensor's sensitivity. The DC-MFC-B's toxicity response was established under the electroactive bacteria inhibition rate function to a specific heavy metal level as well as the recovery of the DC-MFC-B. Results show that the DC-MFC-B was optimized at the operating conditions of 1000 Ω external resistance, COD 300 mg L^-1 and 50 mM K₃Fe(CN)₆ as a catholyte solution. The voltage output of the DC-MFC-B decreased with increasing in the copper and arsenic concentrations. A significant linear relationship between the maximum voltage of the biosensor and the heavy metal concentration was obtained with a coefficient of R² = 0.989 and 0.982 for copper and arsenic, respectively. The study could detect copper (1-10 mg L^-1) and arsenic (0.5-5 mg L^-1) over wider range compared to other studies. The inhibition ratio for both copper and arsenic was proportional to the concentrations, indicating the electricity changes are mainly dependent on the activity of the electrogenic bacteria on the anode surface. Moreover, the DC-MFC-B was also recovered in few hours after being cleaned with a fresh medium. It was found that the concentration of the toxicant effected on the recovery time and the recovery time was varied between 4 and 12 h. In short, this work provided new avenues for the practical application of microbial fuel cells as a heavy metal biosensor.

An Electroanalytical Solution for the Determination of Pb2+ in Progressive Hair Dyes Using the Cork-Graphite Sensor

Lead is one of the most toxic metals for living organisms: once absorbed by soft tissues, it is capable of triggering various pathologies, subsequently bioaccumulating in the bones. In consideration of this, its detection and quantification in products for human consumption and use is of great interest, especially if the procedure can be carried out in an easy, reproducible and economical way. This work presents the results of the electroanalytical determination of lead in three different commercial products used as progressive hair dyes. Analyses were performed by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV) using a composite cork–graphite sensor in 0.5M H₂SO₄ solution or 0.1M acetate buffer (pH 4.5), in the presence and absence of hair dye samples. The H₂SO₄ solution gave better results in terms of analyte sensitivity than the acetate buffer electrolyte. In both cases, well-defined signals for lead were obtained by DPSV analyses, enabling the calibration curve and figures of merit to be determined. The limits of detection (LOD) were found to be approximately 1.06 µM and 1.26 µM in H₂SO₄ and acetate buffer, respectively. The DPSV standard addition method was successfully applied to quantify the lead in hair dye samples, yielding values below 0.45% in Pb. All three analyzed samples were shown to comply with the limit set by the Brazilian Health Regulatory Agency, i.e., 0.6% lead in this type of product. The comparison of the electroanalytical results with those obtained by the reference method, based on the use of inductively coupled plasma optical emission spectrometry (ICP–OES), confirmed that the electroanalytical detection approach is potentially applicable as a strategy for quality control.

An electrochemical sensor based on a MOF/ZnO composite for the highly sensitive detection of Cu(ii) in river water samples

Cu(ii) ions are one of the most common forms of copper present in water and can cause bioaccumulation and toxicity in the human body; therefore, sensitive and selective detection methods are required. Herein, a copper ion sensor based on a UiO-66-NH₂/ZnO composite material is proposed. The UiO-66-NH₂/ZnO nanocomposite was prepared by an ultrasonic mixing method. The morphology and structure of the nanocomposite were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The sensitivity to Cu(ii) is 6.46 μA μM⁻¹ and the detection limit is 0.01435 μM. The composite material is rich in –OH and –NH₂ groups, which are active sites for Cu(ii) adsorption. The UiO-66-NH₂/ZnO-modified electrode has good repeatability and anti-interference ability. The sensor was successfully used for the determination of Cu(ii) in an actual water sample.

Cu(ii) ions are one of the most common forms of copper present in water and can cause bioaccumulation and toxicity in the human body; therefore, sensitive and selective detection methods are required.