Simultaneous Stripping Detection of Pb(II), Cd(II) and Zn(II) Using a Bimetallic Hg-Bi/Single-Walled Carbon Nanotubes Composite Electrode

Benzil Bis-Hydrazone Based Fluorescence 'Turn-on' Sensor for Highly Sensitive and Selective Detection of Zn(II) Ions

In this study, a novel Benzil Bis-Hydrazone (BBH) sensor with two C = N-N = C moieties was designed and synthesized based on the condensation reaction between benzil-dihydrazone (b) and cinnamaldehyde. The BBH probe in dimethylsulfoxide showed extremely weak fluorescence. However, the same solution exhibited an intensive fluorescence enhancement (152-fold) with the introduction of Zn(II) ions. In contrast, no or negligible fluorescence changes were observed when other ions were added. The fluorogenic behavior of BBH towards the examined cations indicated an excellent selectivity of the BBH sensor for Zn(II) cations without any interference from other cations like Fe(II), Mg(II), Cu(II), Co(II), Mn(II), Cr(III), Hg(II), Sn(II), Al(I), La(III), Ca(II), Ba(II), Na(I), K(I), and especially Cd(II). Moreover, the UV-vis spectrophotometric titrations revealed that a 1:1 stoichiometric complex BBH-Zn(II) was formed during the Zn(II) sensing and the binding constant value for this complex was calculated to be equal to 106.8. Further, in order to show the affinity of the BBH sensor for Zn(II) cations, it was deemed necessary to determine the limit of detection (LOD) which was found to equal to 2.5 10-4 M.

Electrochemical determination of zinc(II) using N1-hydroxy-N1,N2-diphenylbenzamidine and multi-walled carbon nanotubes modified carbon paste electrode

In this study, a new carbon paste electrode modified with a laboratory-synthesized ligand, N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) and multi-walled carbon nanotubes (MWCNTs) (HDPBA‒MWCNTs/CPE) has been developed. The modified electrode was applied for preconcentration and voltammetric determination of zinc ions (Zn(II)) by square wave anodic stripping voltammetry (SWASV). The preconcentration of Zn(II) on the electrode surface was performed in 0.1 M Brinton Robinson (B-R) buffer solution (pH 6) at an applied potential of -1.30 V versus Ag/AgCl for 120 s, followed by stripping in the positive potential scan of the SWASV after a quit time of 10 s. Under optimized experimental conditions, the proposed electrode exhibited a wider linear dynamic response for Zn(II) in a concentration range of 0.02-10.00 μM with a detection limit of 2.48 nM. This is due to the excellent metal-chelation property of the ligand, and the good conductivity and large surface area of MWCNTs which significantly improved the sensing performance of the nanocomposite modified electrode. The selectivity of the electrode was studied by evaluating the interference effects of various foreign ions on the peak current of Zn(II). The method exhibited high reproducibility with a relative standard deviation (RSD) of 3.1%. The present method was applied for the determination of zinc ions in water samples. The recovery values in the tested samples were found to be 98.50-106.0%, indicating a good accuracy of the proposed electrode. Furthermore, the electrochemical behavior of HDPBA in acetonitrile and aqueous solutions has been studied.

A fluorescent probe based on a phenylalanine derivative is capable of sequential detection of Zn2+ and Cys/His

A facile and dual fluorescent chemosensor (named 7-IDF) based on a phenylalanine derivative with an indole group was designed and synthesized. 7-IDF can selectively and sensitively detect Zn²⁺ via obvious fluorescence enhancement in an aqueous solution. Remarkably, the 7-IDF-Zn complex with blue luminescence has higher selectivity toward cysteine (Cys) and histidine (His) than for other amino acids. Intriguingly, 7-IDF can also be used as an excellent probe to detect Zn²⁺ in real water samples. Moreover, 7-IDF and 7-IDF-Zn possess excellent biocompatibility and cell permeability, and 7-IDF can consecutively detect Zn²⁺ and Cys/His in Hela cells through fluorescence imaging experiments. This study suggests that the phenylalanine-based chemosensor possesses great potential applications for the sequential detection of Zn²⁺ and Cys/His in biosystems.

Electrochemical Sensing of Lead in Drinking Water Using Copper Foil Bonded with Polymer

Levels of lead (Pb) in tap water that are well below established guidelines are now considered harmful, so the detection of sub-parts-per-billion (ppb) Pb levels is crucial. In this work, we developed a two-step, facile, and inexpensive fabrication approach that involves direct bonding of copper (Cu) and liquid crystal polymer (LCP) followed by polyester resin printing for masking onto Cu/LCP to fabricate Cu thin-film-based Pb sensors. The oxygen plasma-treated surfaces resulted in strongly bonded Cu/LCP with a high peel strength of 500 N/m due to the highly hydrophilic nature of both surfaces. The bonded specimen can withstand wet etching of the electrode and can address delamination of the electrode for prolonged use in application environments. The Cu-foil-based electrochemical sensor showed sensitivity of ~11 nA/ppb/cm² and a limit of detection (LOD) of 0.2 ppb (0.2 µg/L) Pb ions in water. The sensor required only 30 s and a 100 µL sample to detect Pb. To date, this is the most rapid detection of Pb performed using an all-Cu-based sensor. The selectivity test of Cu to Pb with interferences from cadmium and zinc showed that their peaks were separated by a few hundred millivolts. This approach has strong potential towards realizing low-cost, highly reliable integrated water quality monitoring systems.

Self-Assembled Iron Oxide Nanoparticle-Modified APTES-ITO Electrode for Simultaneous Stripping Analysis of Cd(II) and Pb(II) Ions

Carboxyl (-COOH)-stabilized iron oxide nanoparticles (IONPs) synthesized through co-precipitation were used to modify an indium tin oxide (ITO) electrode, which was chemically functionalized with 3-aminopropyltriethoxysilane (APTES) for heavy metal detection. The effect of soaking time (30, 60, 90, and 120 min) of IONP-COOH self-assembled on an APTES-ITO electrode was studied. Cyclic voltammetry and scanning electron microscopy were applied to analyze the electrochemical properties and morphologies of IONP-COOH/APTES-ITO modified electrode. The modified electrodes were then employed for the simultaneous detection of Cd(II) and Pb(II) by using square wave anodic stripping voltammetry. At 90 min of soaking time, excellent electrochemical performance and larger effective surface area (A e) were obtained. The linear range for the simultaneous detection of Cd(II) and Pb(II) ions using the modified electrode was 10-100 ppb with limits of detection of 0.90 and 0.60 ppb, respectively. The interference study revealed a low interference effect from Cr(III), Hg(II), Zn(II), Cu(II), Mg(II), Na(I), and K(I) toward the simultaneous detection of Cd(II) and Pb(II). Finally, the IONP-COOH/APTES-ITO-modified electrode was applied to analyze seawater samples and was able to simultaneously detect Cd(II) and Pb(II) ions.

Conductive electrospun composite fibers based on solid-state polymerized Poly(3,4-ethylenedioxythiophene) for simultaneous electrochemical detection of metal ions

Conductive composite fibers containing poly (3,4-ethylenedioxythiophene) (PEDOT) and silver nanoparticles (AgNPs) were fabricated by emulsion electrospinning of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) in toluene together with aqueous solution of poly (vinyl alcohol) (PVA) and silver nanoparticles (AgNPs) in the presence of sodium dodecylsulfate followed by heat treatment at 70 °C to convert DBEDOT to conductive PEDOT via solid state polymerization (SSP). The composite fibers were characterized by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis. The PEDOT/PVA/AgNPs composite fibers deposited on a screen-printed carbon electrode (SPCE) surface exhibited good electrochemical response and was applied for simultaneous detection of heavy metal ions in a mixture, namely Zn(II), Cd(II), and Pb(II) via square wave anodic stripping voltammetry (SWASV). With added Bi⁺³ into the detection system, the bismuth film formed on the electrode allows effective alloy formation with the deposited heavy metals obtained upon reduction of the heavy metal ions, the detection of heavy metal ions after stripping was successfully accomplished with a linear range of 10-80 ppb and limits of detections (LOD) of 6, 3 and 8 ppb for Zn(II), Cd(II), and Pb(II), respectively.

Bismuth Nanoclusters/Porous Carbon Composite: A Facile Ratiometric Electrochemical Sensing Platform for Pb2+ Detection with High Sensitivity and Selectivity

In this work, a ratiometric electrochemical sensor was constructed for the detection of Pb²⁺ based on a bismuth nanocluster-anchored porous activated biochar (BiNCs@AB) composite. BiNCs with loose structure and AB with abundant oxygen-containing functional groups are favorable for Pb²⁺ adsorption and preconcentration; meanwhile, porous AB provides more mass transfer pathways and increases electronic and ion diffusion coefficients, realizing high sensitivity for Pb²⁺ detection. At the same time, BiNCs were proposed as an inner reference for ratiometric electrochemical detection, which could greatly enhance the determination accuracy. Under optimized experimental conditions, the anodic peak current ratio between Pb²⁺ and BiNCs exhibited a good linear relationship with the concentration from 3.0 ng/L to 1.0 mg/L. The detection limit can be detected down to 1.0 ng/L. Furthermore, the proposed sensor demonstrated good reproducibility, stability, and interference resistance, as well as satisfactory recoveries for the detection of Pb²⁺ in real samples.

Synthesis of Bamboo-like Multiwall Carbon Nanotube-Poly(Acrylic Acid-co-Itaconic Acid)/NaOH Composite Hydrogel and its Potential Application for Electrochemical Detection of Cadmium(II)

A poly(acrylic acid-co-itaconic acid) (PAA-co-IA)/NaOH hydrogel containing bamboo-type multiwall carbon nanotubes (B-MWCNTs) doped with nitrogen (PAA-co-IA/NaOH/B-MWCNTs) was synthesized and characterized by SEM, absorption of water, point of zero charges, infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The possible use of the PAA-co-IA/NaOH/B-MWCNT hydrogel as an electrode modifier and pre-concentrator agent for Cd(II) sensing purposes was then evaluated using carbon paste electrodes via differential pulse voltammetry. The presence of the B-MWCNTs in the hydrogel matrix decreased its degree of swelling, stabilized the structure of the swollen gel, and favored the detection of 3 ppb Cd(II), which is comparable to the World Health Organization's allowable maximum value in drinking water. A calibration curve was obtained in the concentration range of 2.67 × 10^-8 to 6.23 × 10^-7 M (i.e., 3 and 70 ppb) to determine a limit of detection (LOD) of 19.24 μgL^-1 and a sensitivity of 0.15 μC ppb^-1. Also, the Zn(II), Hg(II), Pb(II) and Cu(II) ions interfered moderately on the determination of Cd(II).

Magnetically separable and recyclable bamboo-like carbon nanotube-based FRET assay for sensitive and selective detection of Hg2

The global occurrence of toxic hazards in aquatic ecosystems has aroused concern about the potential impacts on the ecological environment and human health in recent decades. Mercury(II) ions that originate from widespread sources including the mining industry, fossil fuel consumption, and industrial wastes are now well known as a highly toxic pollutant. Despite various detection methods which have been reported to sense Hg²⁺, it still poses a great challenge for us to develop a new effective sensing platform to replenish current fluorescent detection techniques. Here, we report a novel fluorescent biosensor using bamboo-like magnetic carbon nanotubes (BMCNTs) and FAM-labeled T-rich ssDNA for efficient detection of Hg²⁺ in aqueous solution. The proposed biosensor shows a good response toward Hg²⁺ detection over a linear response range of 0.05~1 μM (R² = 0.98) with a detection limit of 20 nM. It also exhibits the capability to discriminate Hg²⁺ ions with negligible response to other metal ions, such as Ca²⁺, Cd²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. Interestingly, the BMCNTs could be separated and recycled easily by using an external magnet, which means a much more cost-effective, easy-to-operate, and eco-friendly method for Hg²⁺ ion detection.

Voltammetry Determination of Pb(II), Cd(II), and Zn(II) at Bismuth Film Electrode Combined with 8-Hydroxyquinoline as a Complexing Agent

A novel method was developed for the simultaneous determination of Pb(II), Cd(II), and Zn(II) based on the cathodic stripping response at a bismuth film electrode associated with oxine as a chelating agent. The developed method provided a high and sharp electrochemical response compared with the method without oxine. A linear response of peak currents was observed for Pb(II), Cd(II), and Zn(II) concentration in the range from 2 ppb to 110 ppb. The detection limits of Pb(II), Cd(II), and Zn(II) were 0.45, 0.17, and 0.78 ppb, respectively. This method was successfully applied to the determination of Pb(II), Cd(II), and Zn(II) in lake-water and river-water samples. The metals were detected at the ultratrace level, showing the feasibility of the proposed method for environmental applications.

Facile synthesis of self-assembled carbon nanotubes/dye composite films for sensitive electrochemical determination of Cd(II) ions

A new type of voltammetric sensor material has been fabricated via a facile self-assembled method. A modified glassy carbon electrode (GCE) by phenylsulfonic groups grafted multi-walled carbon nanotubes (CNT-SO₃H) with dye molecules via Langmuir-Blodgett (LB) assembling (CNT-SO₃H/dye-LB/GCE) were prepared for detecting trace levels of cadmium (Cd²⁺) ions by square wave anodic stripping voltammetry. The synergy effect between CNT-SO₃H and dye as well as orderly aggregates in composite LB films contributed to greatly enhancing the determination performance. Under selected conditions, voltammetric response of the fabricated electrochemical sensor in 0.1 M acetate buffer solution containing Bi³⁺ ions for Cd²⁺ ions was linear with its concentration in the range 0.1 to 1.2 μM, with a detection limit of 0.08 μM. In addition, the preparation process of self-assembled composite film modified electrodes was simple, non-toxic, exhibiting higher sensitivity and potential application prospects in aspects of heavy metal ions detection and environmental analysis.

The effective determination of Cd(ii) and Pb(ii) simultaneously based on an aluminum silicon carbide-reduced graphene oxide nanocomposite electrode

A platform for the simultaneous determination of Cd(ii) and Pb(ii) in aqueous solution has been applied based on an aluminum silicon carbide-reduced graphene oxide nanocomposite (Al₄SiC₄-RGO) modified bismuth film glassy carbon electrode (GCE) using square wave anodic stripping voltammetry (SWASV) for the first time. The Al₄SiC₄-RGO nanocomposite electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with the Al₄SiC₄ modified GCE and bare GCE, the electrochemical performance of the Al₄SiC₄-RGO nanocomposite electrode is obviously enhanced resulting from the synergistic effects of Al₄SiC₄, RGO and bismuth film. The chemical and electrochemical parameters that exert an influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH values, concentrations of Bi³⁺, deposition potentials and deposition times, were carefully studied. Under optimal conditions, a linear relationship exists between the currents and the concentrations of Cd(ii) and Pb(ii) in the range of 50 to 2700 μg L^-1. The limits of detection (S/N = 3) are estimated to be 1.30 μg L^-1 for Pb(ii) and 2.15 μg L^-1 for Cd(ii). Compared with the related work reported in the literature, the analytical performance in this work has a lower determination limit and a wider detection linear range. In addition, this electrode also exhibits good stability and reproducibility. These results imply that the Al₄SiC₄-RGO nanocomposite might be a promising candidate for practical applications in the electrochemical detection of metal ions.

Composites Based on Conducting Polymers and Carbon Nanomaterials for Heavy Metal Ion Sensing (Review)

Current review signifies recent trends and challenges in the development of electrochemical sensors based on organic conducting polymers (OCPs), carbon nanotubes (CNTs) and their composites for the determination of trace heavy metal ions in water are reviewed. OCPs and CNTs have some suitable properties, such as good electrical, mechanical, chemical and structural properties as well as environmental stability, etc. However, some of these materials still have significant limitations toward selective and sensitive detection of trace heavy metal ions. To overcome the limitations of these individual materials, OCPs/CNTs composites were developed. Application of OCPs/CNTs composite and their novel properties for the adsorption and detection of heavy metal ions outlined and discussed in this review.

3D Printed Microfluidic Device with Microporous Mn2O3-Modified Screen Printed Electrode for Real-Time Determination of Heavy Metal Ions

Fabricating portable devices for the determination of heavy metal ions is an ongoing challenge. Here, a 3D printing approach was adopted to fabricate a microfluidic electrochemical sensor with the desired shape in which the model for velocity profiles in microfluidic cells was built and optimized by the finite element method (FEM). The electrode in the microfluidic cell was a flexible screen-printed electrode (SPE) modified with porous Mn₂O₃ derived from manganese containing metal-organic framework (Mn-MOF). The microfluidic device presented superior electrochemical detection properties toward heavy metal ions. The calibration curves at the modified SPE for Cd(II) and Pb(II) covered two linear ranges varying from 0.5 to 8 and 10 to 100 μg L^-1, respectively. The limits of detection were estimated to be 0.5 μg L^-1 for Cd(II) and 0.2 μg L^-1 for Pb(II), which were accordingly about 6 and 50 times lower than the guideline values proposed by the World Health Organization. Furthermore, the microfluidic device was connected to iPad via a USB to enable real-time household applications. Additionally, the sensing system exhibited a better stability and reproducibility compared with traditional detecting system which offered a promising prospect for the detection of heavy metal ions especially in household and resource-limited occasions.

A Fully Integrated and Miniaturized Heavy-metal-detection Sensor Based on Micro-patterned Reduced Graphene Oxide

For this paper, a fully integrated and highly miniaturized electrochemical sensor was designed and fabricated on a silicon substrate. A solvothermal-assisted reduced graphene oxide named "TRGO" was then successfully micro-patterned using a lithography technique, followed by the electrodeposition of bismuth (Bi) on the surface of the micro-patterned TRGO for the electrochemical detection of heavy metal ions. The fully integrated electrochemical micro-sensor was then measured and evaluated for the detection of cadmium and lead-heavy metal ions in an acetic-acid buffered solution using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated micro-sensor exhibited a linear detection range of 1.0 μg L(-1) to 120.0 μg L(-1) for both of the metal ions, and detection limits of 0.4 μg L(-1) and 1.0 μg L(-1) were recorded for the lead and cadmium (S/N = 3), respectively. Drinking-water samples were used for the practical assessment of the fabricated micro-sensor, and it showed an acceptable detection performance regarding the metal ions.

Determination of Cd2+ and Pb2+ Based on Mesoporous Carbon Nitride/Self-Doped Polyaniline Nanofibers and Square Wave Anodic Stripping Voltammetry

The fabrication and evaluation of a glassy carbon electrode (GCE) modified with self-doped polyaniline nanofibers (SPAN)/mesoporous carbon nitride (MCN) and bismuth for simultaneous determination of trace Cd²⁺ and Pb²⁺ by square wave anodic stripping voltammetry (SWASV) are presented here. The morphology properties of SPAN and MCN were characterized by transmission electron microscopy (TEM), and the electrochemical properties of the fabricated electrode were characterized by cyclic voltammetry (CV). Experimental parameters, such as deposition time, pulse potential, step potential, bismuth concentration and NaCl concentration, were optimized. Under the optimum conditions, the fabricated electrode exhibited linear calibration curves ranging from 5 to 80 nM for Cd²⁺ and Pb²⁺. The limits of detection (LOD) were 0.7 nM for Cd²⁺ and 0.2 nM for Pb²⁺ (S/N = 3). Additionally, the repeatability, reproducibility, anti-interference ability and application were also investigated, and the proposed electrode exhibited excellent performance. The proposed method could be extended for other heavy metal determination.

Direct determination of cadmium and lead in pharmaceutical ingredients using anodic stripping voltammetry in aqueous and DMSO/water solutions

A new electrochemical method has been developed to detect and quantify the elemental impurities, cadmium(II) (Cd(2+)) and lead(II) (Pb(2+)), either simultaneously or individually in pharmaceutical matrices. The electro-analytical approach, involving the use of anodic stripping voltammetry (ASV) on an unmodified glassy carbon electrode, was performed in both aqueous and in a 95/5 dimethyl sulfoxide (DMSO)/water solutions, without acid digestion or dry ashing to remove organic matrices. Limits of detection (LODs) in the μg L(-1) [or parts per billion (ppb), mass/volume] range were obtained for both heavy metals - in the presence and absence of representative pharmaceutical components. To the best of our knowledge, the work demonstrates the first analysis of heavy metals in DMSO/water solutions through ASV. The strong reproducibility and stability of the sensing platform, as well as obviation of sample pretreatment show the promise of utilizing ASV as a sensitive, robust, and inexpensive alternative to inductively-coupled-plasma (ICP)-based approaches for the analysis of elemental impurities in, e.g., pharmaceutical-related matrices.