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.

Sensitive sensing of Hg(II) based on lattice B and surface F co-doped CeO2: Synergies of catalysis and adsorption brought by doping site engineering

Transition metal oxides are widely used in the detection of heavy metal ions (HMIs), and the co-doping strategy that introducing a variety of different dopant atoms to modify them can obtain a better detection performance. However, there is very little research on the co-doped transition metal oxides by non-metallic elements for electrochemical detection. Herein, boron (B) and fluorine (F) co-doped CeO2 nanomaterial (BFC) is constructed to serve as the electrochemically sensitive interface for the detection of Hg(II). B and F affect the sensitivity of CeO2 to HMIs when they were introduced at different doping sites. Through a variety of characterization, it is proved that B is successfully doped into the lattice and F is doped on the surface of the material. Through the improvement of the catalytic properties and adsorption capacity of CeO2 by different doping sites, this B and F co-doped CeO2 exhibits excellent square wave anodic stripping voltammetry (SWASV) current responses to Hg(II). Both the high sensitivity of 906.99 μA μM-1 cm-2 and the low limit of detection (LOD) of 0.006 μM are satisfactory. Besides, this BFC glassy carbon electrode (GCE) also has good anti-interference property, which has been successfully used in the detection of Hg(II) in actual water. This discovery provides a useful strategy for designing a variety of non-metallic co-doped transition metal oxides to construct trace heavy metal ion-sensitive interfaces.

Development of a Novel H-Shaped Electrochemical Aptasensor for Detection of Hg2+ Based on Graphene Aerogels-Au Nanoparticles Composite

Hg2+, a highly toxic heavy metal, poses significant environmental and health risks, necessitating rapid detection methods. In this study, we employed an electrochemical aptasensor for rapid and sensitive detection of Hg2+ based on DNA strands (H2 and H3) immobilized graphene aerogels-Au nanoparticles (GAs-AuNPs) hybrid recognition interface and exonuclease III (Exo III)-mediated cyclic amplification. Firstly, Gas-AuNPs were modified on the surface of the ITO electrode to form a sensing interface to increase DNA loading and accelerate electron transfer. Then, DNA helper was generated with the addition of Hg2+ via Exo III-mediated cycling. Finally, the hairpin structures of H2 and H3 were opened with the DNA helper, and then the methylene blue (MB) functionalized DNA (A1 and A2) combined with the H2 and H3 to form an H-shaped structure. The current response of MB as an electrochemical probe was proportional to the concentration of Hg2+. Under optimal conditions, the aptasensor showed excellent performance for Hg2+, achieving a linear range from 1 fM to 10 nM and a detection limit of 0.16 fM. Furthermore, the aptasensor was used to detect Hg2+ in spiked milk samples, achieving a high recovery rate and demonstrating promising application prospects.

Bimodal interferences of Pb(II) induced by parallel deposition in Pb(II)-Cu(II) electrochemical detections: Voltammetric signals analysis combined with numerical simulations on transient interfacial phenomena

The perplexity of double peaks in Pb(II) detections has been a threat to the reliability of Pb(II) electroanalysis results for a long term. For the complexity of electrode interfaces, rare studies were taken on mechanisms of Pb(II) double peaks through interfacial kinetics. In this work, analyses on experimental signals and interfacial simulations were working together to reveal that the generation of Pb(II) double peaks in Pb(II)-Cu(II) systems is the deposition of Pb(II) on Cu deposits occurring in parallel. By applying anode stripping voltammetry and cyclic voltammetry, a parallel deposition reaction was found to influence the shape of Pb(II) peaks, and the existence of the second peak was controlled through the adjustment of experimental conditions. A kinetic model was built to reveal the interference of electroanalysis signals caused by a parallel deposition reaction and simulations based on the model were combined with experiments to illustrate that double peaks of Pb(II) were caused by the parallel deposition on Cu(II) deposits. This work proposes another insight of Pb(II) double peaks from macroscale kinetics and pays more attention on the dynamic procedure of electroanalysis interfaces, which makes the study on environmental electroanalysis interface phenomena more clear and is enlightening to develop efficient electrical methods for pollutant monitoring.

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.

Green synthesis of Piper chaudocanum stem extract mediated silver nanoparticles for colorimetric detection of Hg2+ ions and antibacterial activity

A green synthetic approach to synthesize silver nanoparticles (AgNPs) using the stem extract of Piper chaudocanum for highly sensitive colorimetric detection of Hg²⁺ with a low limit of detection of 23 nM and easy colorimetric read-out has been reported. In addition, the biosynthesized AgNPs demonstrated efficient antibacterial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The morphology and structure of the as-synthesized AgNPs were examined using SEM, TEM, EDX, XRD and FT-IR analyses. The XRD and TEM results confirm the formation of AgNPs with an average particle size of 8-12 nm. The TLC, CC and HPLC revealed that four main compounds, pentacosanoic acid (1), piperine (2), β-sitosterol (3), and campesterol glucoside (4), isolated from P. chaudocanum extract act as reducing and stabilizing agents for AgNP formation, and piperine plays a vital role in green synthesis. The chemical structures of these compounds were determined by ESI MS, FTIR, and one- and two-dimensional NMR spectroscopic data analysis. This approach is an efficient, green, cost-effective, eco-friendly and promising technique for synthesizing AgNPs with applications in the colorimetric detection of Hg²⁺ and antibacterial activity.

Graphene Synthesis Techniques and Environmental Applications

Graphene is fundamentally a two-dimensional material with extraordinary optical, thermal, mechanical, and electrical characteristics. It has a versatile surface chemistry and large surface area. It is a carbon nanomaterial, which comprises sp² hybridized carbon atoms placed in a hexagonal lattice with one-atom thickness, giving it a two-dimensional structure. A large number of synthesis techniques including epitaxial growth, liquid phase exfoliation, electrochemical exfoliation, mechanical exfoliation, and chemical vapor deposition are used for the synthesis of graphene. Graphene prepared using different techniques can have a number of benefits and deficiencies depending on its application. This study provides a summary of graphene preparation techniques and critically assesses the use of graphene, its derivates, and composites in environmental applications. These applications include the use of graphene as membrane material for the detoxication and purification of water, active material for gas sensing, heavy metal ions detection, and CO₂ conversion. Furthermore, a trend analysis of both synthesis techniques and environmental applications of graphene has been performed by extracting and analyzing Scopus data from the past ten years. Finally, conclusions and outlook are provided to address the residual challenges related to the synthesis of the material and its use for environmental applications.

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Siloxene-Functionalized Laser-Induced Graphene via COSi Bonding for High-Performance Heavy Metal Sensing Patch Applications

Here, 2D Siloxene nanosheets are newly applied to functionalize porous laser-induced graphene (LIG) on polydimethylsiloxane, modify the surface chemical properties of LIG, and improve the heterogeneous electron transfer rate. Meanwhile, the newly generated COSi crosslink boosts the binding of LIG and Siloxene. Thus, the Siloxene/LIG composite is used as the basic electrode material for the multifunctional detection of copper (Cu) ions, pH, and temperature in human perspiration. Moreover, to enhance the sensing performance of Cu ions, Siloxene/LIG is further modified by carbon nanotubes (CNTs). The fabricated Siloxene-CNT/LIG-based Cu-ion sensor shows linear response within a wide range of 10-500 ppb and a low detection limit of 1.55 ppb. In addition, a pH sensor is integrated to calibrate for determining the accurate concentration of Cu ions due to pH dependency of the Cu-ion sensor. The polyaniline-deposited pH sensor demonstrates a good sensitivity of -64.81 mV pH^-1 over the pH range of 3-10. Furthermore, a temperature sensor for accurate skin temperature monitoring is also integrated and exhibits a stable linear resistance response with an excellent sensitivity of 9.147 Ω °C^-1 (correlation coefficient of 0.139% °C^-1 ). The flexible hybrid sensor is promising in applications of noninvasive heavy-metal ion detection and prediction of related diseases.

Biogenic synthesis of silver anchored ZnO nanorods as nano catalyst for organic transformation reactions and dye degradation

In this study, we are reporting biogenic synthesis of silver nanoparticles and hydrothermal synthesis of zinc oxide nanoparticles. Using convenient mechanical milling methods, nanocomposites with superior photocatalytic and catalytic properties are synthesized. Herein, we have adopted a green, eco-friendly, and economical route for the synthesis of Ag nanoparticles using Zingiber officinalae rhizome extract in an aqueous solution. The synthesized materials were characterized using UV–Vis spectroscopy, XRD, SEM & FE-SEM, FT-IR, Raman, and a particle size analyzer with zeta potential analysis. The photocatalytic activities of Ag, ZnO and their composites were studied by observing the degradation of methylene blue and crystal violet dyes under natural sunlight. Then the catalytic efficacies of synthesized nanoparticles for various organic transformation reactions were studied. Ag–ZnO nanocomposites were predicted to have improved photocatalytic activity and organic transformation reactions, allowing them to be used in environmental remediation applications.

Ultrasensitive Electrochemical Impedance Chiral Discrimination and Sensing of Tryptophan Isomers Based on Core-Shell-Structured Au-Ag Nanoparticles

Au-Ag nanoparticles (Au-Ag NPs) with a core-shell structure are prepared and used for ultrasensitive electrochemical impedance (EI) discrimination of the isomers of tryptophan (Trp). As revealed by circular dichroism, rotary polarization caused by the Au-Ag NPs is consistent with D-Trp but opposite to L-Trp, and thus, the Au-Ag NPs can selectively combine with D-Trp through preferential interactions. Compared with Au-Ag NPs, the composites of D-Trp and Au-Ag NPs (Au-Ag NPs/D-Trp) display significantly increased charge transfer resistance (R_ct); differently, the R_ct of Au-Ag NPs/L-Trp remains almost unchanged because the Au-Ag NPs exhibit poor affinity toward L-Trp. Therefore, ultrasensitive EI enantiodiscrimination of the isomers of Trp is realized even at an extremely low concentration of the Trp isomers (0.1 nM). In addition, it is successfully applied in the ultrasensitive determination of D-Trp at a low concentration level (0.1 nM∼10 μM).

Nanostructured Shell-Layer Artificial Antibody with Fluorescence-Tagged Recognition Sites for the Trace Detection of Heavy Metal Ions by Self-Reporting Microsensor Arrays

Herein, a strategy for a metal ion-imprinted artificial antibody with recognition sites tagged by fluorescein was carried out to construct the selective sites with a sensitive optical response signal to the specific metal ion. The synthesized silica nanoparticles were modified by the derivative residue group of 3-aminopropyltriethoxysilane conjugated with a 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl) molecule through the hydrolysis and condensation reactions. The as-prepared silica nanoparticles were encapsulated by metal ion (Cu²⁺, Cd²⁺, Hg²⁺, and Pb²⁺)-imprinted polymers with nanostructured layers through the copolymerization of ethyl glycol dimethyl methacrylate (EGDMA) as a cross-linker, AIBN as an initiator, metal ions as template molecules, AA as a functional monomer, and acetonitrile as a solvent. The layers of molecular imprinted polymers (MIPs) with a core-shell structure removed template molecules by EDTA-2Na to retain the cavities and spatial sizes to match the imprinted metal ions. The microsensor arrays were achieved by the self-assembly technique of SiO₂@MIP nanoparticles on the etched silicon wafer with regular dot arrays. The nanostructured-shell layers with fluorescence-tagged recognition sites rebound metal ions by the driving force of concentration difference demonstrates the high selective recognition and sensitive detection to heavy metal ions through the decline of fluorescence intensity. The LOD concentration for four metal ions is down to 10^-9 mol·L^-1. The method will provide biomimetic synthesis, analyte screen, and detection of highly dangerous materials in the environment for theoretical foundation and technological support.

Bio-mimetic synthesis of catalytically active nano-silver using Bos taurus (A-2) urine

Herein we have synthesized silver nanoparticles (Ag NPs) using liquid metabolic waste of Bos taurus (A-2 type) urine. Various bio-molecules present in cow urine, are effectively used to reduce silver (Ag) ions into silver nanoparticles in one step. This is bio-inspired electron transfer to Ag ion for the formation of base Ag metal and is fairly prompt and facile. These nanoparticles act as a positive catalyst for various organic transformation reactions. The structural, morphological, and optical properties of the as-synthesized Ag NPs are widely characterized by X-ray diffraction spectroscopy, ultraviolet–visible spectroscopy, scanning electron microscope, Fourier transmission infra-red spectroscopy, and atomic force microscopy. The as-synthesized bio-mimetic Ag NPs show potential activity for several reduction reactions of nitro groups. The Ag NPs were also used for degradation of hazardous dyes such as Methylene blue and Crystal violet with good degradation rate constant.

Novel Aminosilane (APTES)-Grafted Polyaniline@Graphene Oxide (PANI-GO) Nanocomposite for Electrochemical Sensor

Lead is a potentially toxic element (PTE) that has several adverse medical effects in humans. Its presence in the environment became prominent due to anthropogenic activities. The current study explores the use of newly developed composite materials (organic-inorganic hybrid) based on PANI-GO-APTES for electrochemical detection of Pb²⁺ in aqueous solution. The composite material (PANI-GO-APTES) was synthesized by chemical method and was characterized with SEM, XPS, XEDS, XRD, TGA, FTIR, EIS and CV. The result of characterization indicates the successful synthesis of the intended material. The PANI-GO-APTES was successfully applied for electrochemical detection of Pb²⁺ using cyclic voltammetry and linear sweep voltammetry method. The limit of detection of Pb²⁺ was 0.0053 µM in the linear range of 0.01 µM to 0.4 µM. The current response produced during the electrochemical reduction of Pb²⁺ catalyzed by PANI-GO-APTES was also very repeatable, reproducible and rapid. The application of PANI-GO-APTES-modified GCE in real sample analysis was also established. Therefore, PANI-GO-APTES is presented as a potential Pb²⁺ sensor for environmental and human health safety.

Studies on a glutathione coated hollow ZnO modified glassy carbon electrode; a novel Pb(ii) selective electrochemical sensor

Herein, we report the electrochemical detection of heavy metal ions such as Pb(ii), Cd(ii) and Hg(ii) ions while using glutathione coated hollow ZnO modified glassy carbon electrode (Glu-h-ZnO/GCE). An excellent voltammetric response of the modified electrode towards these metal ions was observed by different voltammetric techniques. Among the different target metal ions, a selective electrochemical response (sensitivity = 4.57 μA μM-1) for the detection of Pb(ii) ions was obtained with differential pulse voltammetric (DPV) measurements. Besides, under optimal experimental conditions and in the linear concentration range of 2-18 μM, a very low detection limit of 0.42 μM was obtained for Pb(ii) ion. The observed electrochemical behaviour of Glu-h-ZnO/GCE towards these metal ions is in conformity with the band gap of the composite in the presence of various test metal ions. The band gap studies of the composite and various "Composite-Metal Ion" systems were obtained by reflectance as well as by computational methods where results are in close agreement, justifying the observed electrochemical behaviour of the systems. The lowest band gap value of the "Composite-Pb" system may be the reason for the excellent electrochemical response of the Glu-h-ZnO modified GCE towards the detection of Pb(ii) ion.

Anodic Stripping Voltammetry with the Hanging Mercury Drop Electrode for Trace Metal Detection in Soil Samples

The widely spread use of the hanging mercury drop electrode (HMDE) for multi-ion analysis is primarily ascribed to the following reasons: (i) excellent reproducibility owing to the easy renewal of the electrode surface avoiding any hysteresis effect (i.e., a new identical drop is generated for each measurement to be accomplished); (ii) a wide cathodic potential window originating from the passive hydrogen evolution and solvent electrolysis; (iii) the ability to form amalgams with many redox-active metal ions; and (iv) the achievement of (sub)nanomolar limits of detection. On the other hand, the main controversy of the HMDE usage is the high toxicity level of mercury, which has motivated the scientific community to question whether the HMDE deserves to continue being used despite its unique capability for multi-metal detection. In this work, the simultaneous determination of Zn2+, Cd2+, Pb2+, and Cu2+ using the HMDE is investigated as a model system to evaluate the main features of the technique. The analytical benefits of the HMDE in terms of linear range of response, reproducibility, limit of detection, proximity to ideal redox behavior of metal ions and analysis time are herein demonstrated and compared to other electrodes proposed in the literature as less-toxic alternatives to the HMDE. The results have revealed that the HMDE is largely superior to other reported methods in several aspects and, moreover, it displays excellent accuracy when simultaneously analyzing Zn2+, Cd2+, Pb2+, and Cu2+ in such a complex matrix as digested soils. Yet, more efforts are required towards the definitive replacement of the HMDE in the electroanalysis field, despite the elegant approaches already reported in the literature.

Synthesis of Silver and Gold Nanoparticles from Rumex roseus Plant Extract and Their Application in Electrochemical Sensors

The room-temperature synthesis of silver (AgNPs) and gold (AuNPs) nanoparticles from aqueous solution of AgNO3 and HAuCl4 respectively, using Rumex roseus (RR) plant extract as a reducing agent, is reported here for the first time. The nanoparticles obtained were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The formation of nanoparticles with spherical-shaped morphology was verified by TEM and confirmed by UV-Vis spectroscopy through the analysis of Ag and Au plasmon resonance peak and DLS measurements. New electrochemical sensors have been developed by employing the synthesized Ag and Au nanoparticles as modifiers of glassy carbon electrode (GCE) and screen-printed carbon electrode (SPCE), respectively. The AgNPs-modified GCE was investigated for the electrochemical determination of hydrogen peroxide (H2O2). Further enhancement of electrochemical performances was obtained using a nanocomposite made of AgNPs and reduced graphene oxide (rGO)-modified GCE. The AuNPs-SPCE sensor was instead tested in the electrochemical sensing of riboflavin (RF). To our knowledge, this is the first paper reporting Rumex roseus plant extract as a source for the synthesis of metal nanoparticles and their use for developing simple, sensitive and reliable electrochemical sensors for H2O2 and RF.

Silver nanoparticle driven signal amplification for electrochemical chiral discrimination of amino acids

β-Cyclodextrin (β-CD) modified silver nanoparticles (AgNPs), denoted as β-CD/AgNPs, were prepared by a simple one-pot method. Due to the inherent chirality of β-CD, the developed β-CD/AgNPs exhibited higher affinity toward l-tyrosine (l-Tyr) than d-tyrosine (d-Tyr), leading to serious aggregation of AgNPs in the presence of l-Tyr. Consequently, the l-Tyr induced aggregation of AgNPs can result in signal amplification in the differential pulse voltammograms (DPVs) of l-Tyr, which can be applied for the electrochemical chiral discrimination of the Tyr enantiomers. Other chiral amino acids including tryptophan and phenylalanine can also be successfully discriminated with the β-CD/AgNPs, suggesting high universality of the developed chiral sensor.

Evaluation of a Reduced Graphene Oxide-Sb Nanoparticles Electrochemical Sensor for the Detection of Cadmium and Lead in Chamomile Tea

The development of electroanalytical sensors for heavy metals detection in complex matrices holds great interest. Herein, a sensor based on a reduced graphene oxide (rGO) modified with antimony nanoparticles (Sb) was developed for the electrochemical detection of divalent cadmium ions (Cd2+) and lead ions (Pb2+). The simultaneous determination of both metals covered a range of 0.1 to 3.0 µmol L−1, with limits of detection (LOD) of 70.03 and 45.50 nmol L−1 for Cd2+ and Pb2+, respectively. For the individual detection, LOD of 20.50 nmol L−1 (Cd2+) and 2.01 nmol L−1 (Pb2+) were found. The analytical performance of this new sensor in detecting both metals in chamomile tea samples was satisfactorily evaluated.

Effective disposal of methylene blue using green immobilized silver nanoparticles on graphene oxide and reduced graphene oxide sheets through one-pot synthesis

This study reveals the feasibility of exploring highly efficient, cost-effective, and stable green adsorbents for the treatment of contaminated water. Here silver nanoparticles (AgNPs) were immobilized onto nanosheets of graphene oxide (GO) through in situ reduction process using green tea aqueous extract. GO reduction to reduced graphene oxide (rGO) and AgNPs decoration on rGO also occurred simultaneously. The impacts of the extract concentration, contact time, and temperature on the synthesis process have been investigated. The synthesized nanocomposites were examined by XRD, FTIR, Raman, SEM, TEM, and TGA. The GO nanosheets were decorated by AgNPs with a crystalline structure and an average particle size of 25 ± 3 nm. The temperature and the extract concentration were considerably affecting the type of the resulting nanocomposites. The GO/Ag nanocomposites were formed at room temperature (27 °C) using different extract concentration (2-18% (v/v)), while the rGO/Ag nanocomposite was formed only at a higher temperature (95 °C) with higher extract concentration (18%). The methylene blue (MB) dye was picked as a water pollutant to explore the adsorption ability of the nanocomposites. The adsorption behavior of the GO/Ag nanocomposites was examined under diverse factors (MB concentration, adsorbent dosage, pH, and contact time) to achieve optimization. The adsorption data concurs with Langmuir isotherm giving maximum adsorption up to 633 mg g^-1. Adsorption kinetics demonstrate good pseudo-second-order compliance. Spontaneous and endothermic nature of adsorption was affirmed via thermodynamic parameters. The nanocomposites could be utilized as eco-friendly and reliable adsorbents in wastewater treatment, as a result of their exceptional productivity and reusing potential.

Ratiometric electrochemical sensor for sensitive detection of sunset yellow based on three-dimensional polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin

Electrochemical methods have been deemed effective strategies for the detection of dye additive sunset yellow (SY) owing to their low cost, good stability, and high sensitivity. However, the application of the existing sensors with single electrical signal response is limited by their inadequate sensitivity and large background interference. Herein, a ratiometric electrochemical strategy with a dual signal was developed to detect SY. The strategy had an intrinsic built-in correction to the effects from the system, and thus reduced the influence of environmental change. 3D polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin (PEI-rGAs@AuNPs/SH-β-CD) was used as the sensing material due to its 3D macroporous microstructure with high specific surface area and excellent electronic conductivity. Guest molecule methylene blue (MB) was chosen as a probe molecule, which formed an inclusion host-guest complex with a SH-β-CD host in advance. The target molecule SY displaced MB from the CD cavities, resulting in the decrease of MB current and the increase of SY current. With the logarithmic value of I_SY/I_MB as the readout signal, the detection limit of the developed ratiometric electrochemical sensor reached as low as 0.3 nM, confirming the excellent sensitivity. Furthermore, this strategy exhibited good selectivity and repeatability, and could be used for the detection of SY in a real sample.

Graphene-derived nanomaterials as recognition elements for electrochemical determination of heavy metal ions: a review

This review (with 155 refs.) summarizes the progress made in the past few years in the field of electrochemical sensors based on graphene-derived materials for the determination of heavy metal ions. Following an introduction of this field and a discussion of the various kinds of modified graphenes including graphene oxide and reduced graphene oxide, the review covers graphene based electrodes modified (or doped) with (a) heteroatoms, (b) metal nanoparticles, (c) metal oxides, (d) small organic molecules, (e) polymers, and (f) ternary nanocomposites. Tables are provided that afford an overview of representative methods and materials for fabricating electrochemical sensors. Furthermore, sensing mechanisms are discussed. A concluding section presents new perspectives, opportunities and current challenges. Graphical Abstract Schematic illustration of electrochemical sensor for heavy metal ion sensing based on heteroatom-doped graphene, metal-modified graphene, metal-oxide-modified graphene, organically modified graphene, polymer-modified graphene, and ternary graphene based nanocomposites.

Facile synthesis of g-C3N4 with various morphologies for application in electrochemical detection

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). The results obtained using square wave anodic stripping voltammetry (SWASV) showed that when g-C₃N₄ was applied as an electrochemical sensor, it exhibited excellent sensitivity and selectivity for the detection of heavy metal ions including Pb(ii), Cu(ii) and Hg(ii). Compared to nanoporous graphitic carbon nitride (npg-C₃N₄) and g-C₃N₄ nanosheet-modified glass carbon electrode (GCE), g-C₃N₄ successfully realized the individual and simultaneous detection of four target heavy ions for the first time. In particular, g-C₃N₄ displayed significant electrocatalytic activity towards Hg(ii) with a good sensitivity of 18.180 μA μM⁻¹ and 35.923 μA μM⁻¹ under the individual and simultaneous determination conditions, respectively. The sensitivity for simultaneous determination was almost 2 times that of the individual determination. Moreover, the fabricated electrochemical sensor showed good anti-interference, stability and repeatability; this indicated significant potential of the proposed materials for application in high-performance electrochemical sensors for the individual and simultaneous detection of heavy metal ions.

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods.

A novel turn-on fluorescent probe for the multi-channel detection of Zn2+ and Bi3+ with different action mechanisms

A novel multifunctional sensor, RSPT, was identified and developed for multichannel turn-on fluorescent responses to Zn²⁺ and Bi³⁺ in practice.

Ag Nanoparticles Drop-Casting Modification of Screen-Printed Electrodes for the Simultaneous Voltammetric Determination of Cu(II) and Pb(II)

A new silver nanoparticle modified screen-printed electrode was developed and applied to the simultaneous determination of Pb(II) and Cu(II). Two different types of silver nanoparticles with different shapes and sizes, Ag nanoseeds and Ag nanoprisms, were microscopically characterized and three different carbon substrates, graphite, graphene and carbon nanofibers, were tested. The best analytical performance was achieved for the combination of Ag nanoseeds with a carbon nanofiber modified screen-printed electrode. The resulting sensor allowed the simultaneous determination of Pb(II) and Cu(II) at trace levels and its applicability to natural samples was successfully tested with a groundwater certified reference material, presenting high reproducibility and trueness.