Nanocomposite Platform Based on EDTA Modified Ppy/SWNTs for the Sensing of Pb(II) Ions by Electrochemical Method

Facile colorimetric sensor using oxidase-like activity of octahedral Ag2O particles for highly selective detection of Pb(II) in water

Pb(II) is a prevalent heavy metal ion classified as a 2B carcinogen. Excessive intake of Pb(II) in the human body can damage the central nervous system, kidneys, liver, and immune system, leading to permanent brain damage, anemia, and cancer. Colorimetry can be applied to rapidly determine Pb(II) residues, but there are still many challenges in the accuracy and sensitivity of detection. Based on the inhibitory impact of Pb(II) on the oxidase-like activity of octahedral silver oxide (Ag2O), a colorimetric sensor with smartphone-assisted analysis for the Pb(II) detection was first developed. Herein, it has been found that Pb(II) can adsorb onto the surface of octahedral Ag2O, hindering the production of O2- in the reaction system. This ultimately results in the suppression of oxidase-like activity, leading to a lighter purple appearance of the colorimetric reaction solution. The sensor exhibits a high degree of sensitivity and a limit of detection (LOD) for Pb(II) was calculated as 2.2 μg L-1. Hence, the developed colorimetric sensor with high sensitivity, excellent specificity, and high tolerance to sodium ions is hopeful to have practical applications in Pb(II) detection in environmental water samples. Moreover, the sensor will provide a novel strategy for heavy metal ion detection and other substances.

Dual-functional DNAzyme powered CRISPR-Cas12a sensor for ultrasensitive and high-throughput detection of Pb2+ in freshwater

Freshwater lead pollution has posed severe threat to the environment and human health, underscoring the urgent necessity for accurate and user-friendly detection methods. Herein, we introduce a novel Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR-Cas) sensor for highly sensitive Pb2+ detection. To accomplish this, we designed a dual-functional deoxyribozyme (df-DNAzyme) probe that functions as an activator for the CRISPR-Cas12a system while also recognizing Pb2+. The df-DNAzyme probe was subsequently combined with gold nanoparticles (AuNPs) to fabricate a DNAzyme/AuNP nanoprobe, facilitating the activation of CRISPR-Cas12a in a one-to-multiple manner. Upon exposure to Pb2+, the df-DNAzyme is cleaved, causing disintegration of the DNAzyme/AuNP nanoprobe from magnetic beads. The degraded DNAzyme/AuNP containing multiple double-stranded DNA activators efficiently triggers CRISPR-Cas12a activity, initiating cleavage of fluorescence-quenched reporter DNA and generating amplified signals accordingly. The amplified fluorescence signal is accurately quantified using a quantitative polymerase chain reaction (qPCR) instrument capable of measuring 96 or 384 samples simultaneously at the microliter scale. This technique demonstrates ultra-sensitive detection capability for Pb2+ at concentrations as low as 1 pg/L within a range from 1 pg/L to 10 μg/L, surpassing limits set by World Health Organization (WHO) and United States Environmental Protection Agency (US EPA) guidelines. This study offers an ultrasensitive and high-throughput method for the detection of Pb2+ in freshwater, thereby advancing a novel approach towards the development of precise and convenient techniques for detecting harmful contaminants.

Fluorescence biosensor for ultrasensitive detection of the available lead based on target biorecognition-induced DNA cyclic assembly

A fluorescence biosensor was developed for the ultrasensitive detection of the available lead in soil samples by coupling with DNAzyme and hairpin DNA cyclic assembly. The biorecognition between lead and 8-17 DNAzyme will cleave the substrate strands (DNA2) and release the trigger DNA (T), which can be used to initiate the DNA assembly reactions among the hairpins (H1, H2, and H3). The formed Y-shaped sensing scaffold (H1-H2-H3) contains active Mg2+-DNAyzmes at three directions. In the presence of Mg2+, the BHQ and FAM modified H4 will be cleaved by the Mg2+-DNAyzme to generate a high fluorescence signal for lead monitoring. The linear range of the fluorescence biosensor is from 1 pM to 100 nM and the detection limit is 0.2 pM. The biosensor also exhibited high selectivity and the nontarget competing heavy metals did not interfere with the detection results. Compare with the traditional method (DTPA+ICP-MS) for the available lead detection, the relative error (Re) is in the range from -8.3 % to 9.5 %. The results indicated that our constructed fluorescence biosensor is robust, accurate, and reliable, and can be applied directly to the detection of the available lead in soil samples without complex extraction steps.

Recent advances in the modification of electrodes for trace metal analysis: a review

This review paper summarizes the research published in the last five years on using different compounds and/or materials as modifiers for electrodes employed in trace heavy metal analysis. The main groups of modifiers are identified, and their single or combined application on the surface of the electrodes is discussed. Nanomaterials, film-forming substances, and polymers are among the most used compounds employed mainly in the modification of glassy carbon, screen-printed, and carbon paste electrodes. Composites composed of several compounds and/or materials have also found growing interest in the development of modified electrodes. Environmentally friendly substances and natural products (mainly biopolymers and plant extracts) have continued to be included in the modification of electrodes for trace heavy metal analysis. The main analytical performance parameters of the modified electrodes as well as possible interferences affecting the determination of the target analytes, are discussed. Finally, a critical evaluation of the main findings from these studies and an outlook discussing possible improvements in this area of research are presented.

Recent Advances in Polymer-Based Biosensors for Food Safety Detection

The excessive use of pesticides and drugs, coupled with environmental pollution, has resulted in the persistence of contaminants on food. These pollutants tend to accumulate in humans through the food chain, posing a significant threat to human health. Therefore, it is crucial to develop rapid, low-cost, portable, and on-site biosensors for detecting food contaminants. Among various biosensors, polymer-based biosensors have emerged as promising probes for detection of food contaminants in recent years, due to their various functions such as target binding, enrichment, and simple signal reading. This paper aims to discuss the characteristics of five types of food pollutants-heavy metals, pesticide residues, pathogenic bacteria, allergens, and antibiotics-and their adverse effects on human health. Additionally, this paper focuses on the principle of polymer-based biosensors and their latest applications in detecting these five types of food contaminants in actual food samples. Furthermore, this review briefly examines the future prospects and challenges of biosensors for food safety detection. The insights provided in this review will facilitate the development of biosensors for food safety detection.

Development of a new electrochemical method for the determination of copper(ii) at trace levels in environmental and food samples

This paper presents the fabrication of a new modified carbon paste electrode (CPE) with N 1-hydroxy-N 1,N 2-diphenylbenzamidine (HDPBA) and functionalized multi-walled carbon nanotubes (MWCNTs) (HDPBA-MWCNTs/CPE) for highly sensitive and selective determination of Cu(ii) using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated electrode was characterized using various spectroscopic techniques to study its morphological, structural, and electrochemical properties. The accumulation of Cu(ii) on the surface of HDPBA-MWCNTs/CPE was done in 0.1 M ammonium chloride (NH4Cl, pH 5) solution at an applied potential of -0.70 V versus Ag/AgCl for 180 s, followed by electrochemical stripping in the positive scan of the voltammetry after a resting time of 10 s. The developed HDPBA-MWCNTs/CPE was found to be highly selective, sensitive and reproducible. At optimal conditions of the experiment, the proposed method exhibited a very low limit of detection (0.0048 nM Cu(ii)), a wide linear dynamic range (0.00007-1.5000 μM Cu(ii)), and good reproducibility with relative standard deviation (RSD) value of 3.7%. The effect of various foreign ions on the voltammetric response of Cu(ii) was investigated and the electrode was found to be highly selective to Cu(ii). The practical applicability of the proposed HDPBA-MWCNTs/CPE was studied by applying the electrode for the quantification of Cu(ii) contents in environmental water (wastewater and tap water), soft drink (Fanta and Sprite), and food supplement (commercially available multi-mineral/vitamin tablets) samples. The present method was validated with atomic absorption spectrometry (AAS). The results found from the two methods are in good agreement with a 95% confidence level.

An electroactive montmorillonite/polypyrrole ion exchange film: Ultrahigh uptake capacity and ion selectivity for rapid removal of lead ions

Contact with trace heavy metal contaminants will also lead to extremely bad health influence on human body and aquatic life. Although various adsorbents have been synthesized for the recovery of heavy metal ions, most of them shows deficient adsorption capacity, sluggish uptake rate and low selectivity. In this study, a montmorillonite/polypyrrole (MMT/PPy) film was successfully synthesized by intercalating polymers PPy into the interlayer of MMT nanosheets for selective and rapid capture of Pb²⁺. The electroactive film has ultrahigh uptake capacity (1373.29 mg⋅g^-1), which is much higher than most conventional Pb²⁺ adsorbents. Meanwhile, it had an extreme selectivity towards Pb²⁺ due to the MMT/PPy film can accurately identified Pb²⁺. Through characterization testing and data analysis, the selective and rapid uptake/release of Pb²⁺ should be realized through three ways: (1) negatively-charged laminates of MMT can generate electrostatic attraction to Pb²⁺; (2) -OH on the surface of MMT laminates can accurately identified and bonded with Pb²⁺ (M-O-H↔ M-O-Pb); (3) PPy doped by PSS^n- and protic acid can rapidly catch Pb²⁺ (PPy⁺·PSS^n-+Pb²⁺+e^-→ PPy·PSS^n-·Pb²⁺). Therefore, such a novel MMT/PPy nanocomposite film could has evident application prospect to remove Pb²⁺ from various water bodies.

Electrochemical Analysis of Heavy Metal Ions Using Conducting Polymer Interfaces

Conducting polymers (CPs) are highly conjugated organic macromolecules, where the electrical charge is transported in intra- and inter-chain pathways. Polyacetylene, polythiophene and its derivatives, polypyrrole and its derivatives, and polyaniline are among the best-known examples. These compounds have been used as electrode modifiers to gain sensitivity and selectivity in a large variety of analytical applications. This review, after a brief introduction to the electrochemistry of CPs, summarizes the application of CPs’ electrode interfaces towards heavy metals’ detection using potentiometry, pulse anodic stripping voltammetry, and alternative non-classical electrochemical methods.

A Novel Carbon Paste Electrode Modified with N1-Hydroxy-N1,N2-Diphenylbenzamidine for the Electrochemical Determination of Cadmium(II) in Environmental Samples

The present study introduces a novel electrode for rapid, highly sensitive, and selective electrochemical sensor for cadmium(II) using 5% N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) modified carbon paste electrode (CPE) (HDPBA‒CPE). Surface characterizations and structural analysis of the proposed HDPBA‒CPE were performed using several analytical techniques. The voltammetric measurements of Cd(II) were conducted by cyclic voltammetry (CV) and square wave anodic stripping voltammetry (SWASV). Several experimental conditions such as composition and pH of buffer solutions, HDPBA composition, accumulation potential and time, and other voltammetric conditions were optimized. Cd(II) was preconcentrated on the modified electrode surface for 270 s using Britton Robinson (B-R) buffer (0.1 M, pH 4) at -1.0 V versus Ag/AgCl, followed by electrochemical oxidation of the accumulated Cd(II) in the positive scan of SWASV after a quiet time of 10 s. Under optimized parameters, the proposed method showed a linear range of 0.3-100 nM Cd(II) with a detection limit of 0.032 nM. The fabricated HDPBA-modified carbon paste electrode exhibited excellent sensitivity, selectivity, stability, and reproducibility (with RSD of 3.8%). The developed HDPBA‒CPE was used for the quantification of Cd(II) in tobacco and environmental water samples, and it was found to be applicable for the determination of different types of real samples.

Cobalt encapsulated in bamboo-like N-doped carbon nanotubes for highly sensitive electroanalysis of Pb(II): enhancement based on adsorption and catalysis

Carbon nanotubes (CNTs) are recognized as desirable candidates to fabricate electrochemical sensing interfaces owing to their high surface area and excellent electron conductivity. However, the poor catalytic properties of CNTs significantly hinder their further application in electrochemical detection. Herein, for the first time we combined defective CNTs with catalytically active cobalt nanoparticles (Co NPs) to give cobalt encapsulated in a bamboo-like N-doped carbon nanotube nanocomposite (Co/N-CNTs). The novel constructed Co/N-CNTs are used as a modifier on a bare glass carbon electrode for the electrochemical detection of Pb(ii). As a result, the positive effect of adsorption and catalysis on Co/N-CNT shows a significant improvement in the electroanalytical performance towards Pb(ii) with a sensitivity of 69.74 μA μM-1 and a limit of detection of 0.039 μM. Moreover, the stability and practical applications of Co/N-CNTs towards Pb(ii) in real water samples obtained from a mining subsidence area were also considered. This method shows great promise, achieving an outstanding electroanalysis efficiency with noble-metal-free nanocomposite sensors based on the combination of carbon and transition metals.

Rationally engineered nanosensors: A novel strategy for the detection of heavy metal ions in the environment

Heavy metal ions (HMIs) have been mainly originated from natural and anthropogenic agents. It has become one of biggest societal issues due to their recognised accumulative and toxic effects in the environment as well as biological media. Key measures are required to reduce the risks posed by toxic metal pollutants existing in the environment. The increased research activities of HMIs detection, and use of technologies based on electrochemical detection that combine with engineered nanomaterials, is a key promising and innovative strategy that can potentially confine heavy metal poisoning. Deep understanding of the characteristics of the physicochemical properties of nanomaterials is highly required. It is also important to interpret the parameters at the nano-bio interface level that merely affect cross-interactions between nanomaterials and HMIs. Therefore, the authors outlined the state-of-the-art techniques that used engineeringly developed nanomaterials to detect HMIs in the environment. The possible novel applications of extensive and relatively low-cost HMIs monitoring and detection are discussed on the basis of these strengths. Finally, it is concluded by providing gist on acquaintance with facts in the present-day scenario along with highlighting areas to explore the strategies to overcome the current limitations for practical applications is useful in further generations of nano-world.

Two-dimensional black phosphorus nanoflakes: A coreactant-free electrochemiluminescence luminophors for selective Pb2+ detection based on resonance energy transfer

As a nondegradable environmental pollutant, lead ion (Pb²⁺) has been proven to be deleterious for environmental and health. Conveniently, quickly and accurately on-site detection of Pb²⁺ is of paramount importance. Herein, an electrochemiluminescence (ECL) assay protocol using two-dimensional black phosphorus (2D BP) nanoflakes as new ECL emitter for highly sensitive and selective trace Pb²⁺ was designed on the basis of Pb²⁺ induced ECL resonance energy transfer (ECL-RET) between 2D BP nanoflakes and Ag/AgCl nanocubes. Anodic green ECL emission of BP nanoflakes without any coreactants was achieved. It is noteworthy that the possible ECL mechanism and the influence of coreactants on the ECL behaviour of BP nanoflakes were further investigated. Benefitting from the well match between the ECL emission spectrum of BP nanoflakes (∼510 nm) and the absorption spectrum of Ag/AgCl nanocubes (200-300 nm and 400-700 nm), effective energy transfer yielded. The introduction of Pb²⁺ would lead to the detachment of Ag/AgCl nanocubes then result in an enhanced ECL emission. Based on this, the proposed method could accurately quantify the Pb²⁺ in the range from 0.5 pM to 5 nM, which exhibited comparative performance to previous work. Furthermore, this study presents the example of employing 2D BP nanoflakes as ECL emitters and constructing a coreactant-free ECL sensing platform, which might open up a promising route for the potential design and implement in clinical analysis.

Detection of Pb(II): Au Nanoparticle Incorporated CuBTC MOFs

In the present investigation, copper benzene tricarboxylate metal organic frameworks (CuBTC MOF) and Au nanoparticle incorporated CuBTC MOF (Au@CuBTC) were synthesized by the conventional solvothermal method in a round bottom flask at 105°C and kept in an oil bath. The synthesized CuBTC MOF and Au@CuBTC MOFs were characterized by structure using X-ray diffraction (XRD) spectroscopic methods including Fourier Transform Infrared spectroscopy, Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Energy dispersive spectroscopy (EDS). We also characterized them using morphological techniques such as Field emission scanning electron microscopy (FE-SEM), and electrochemical approaches that included cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We examined thermal stability by thermogravimetric analysis (TG/DTA) and N₂ adsorption—desorption isotherm by Brunauer-Emmett-Teller (BET) surface area method. Both materials were tested for the detection of lead (II) ions in aqueous media. Au nanoparticle incorporated CuBTC MOF showed great affinity and selectivity toward Pb²⁺ ions and achieved a lower detection limit (LOD) of 1 nM/L by differential pulse voltammetry (DPV) technique, which is far below than MCL for Pb²⁺ ions (0.03 μM/L) suggested by the United States (U.S.) Environmental Protection Agency (EPA) drinking water regulations.

Potentiometric extractive sensing of lead ions over a nickel oxide intercalated chitosan-grafted-polyaniline composite

The present research paper reports the extractive potentiometric sensing of lead ions over a chemically functionalized ternary nanocomposite of nickel oxide intercalated chitosan grafted polyaniline (NiO-in-CHIT-g-PANI) prepared by the in situ chemical polymerization and composite formation technique under optimized conditions. The structural, morphological, and physical properties of the composite material were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and other suitable ASTM methods. The obtained analytical result suggests the formation of a porous hybrid composite matrix with better electrical conductivity ∼ 5.25 × 10^-3 S cm^-1, free interactive carbonyl sites, and evolved aligned crystallinity. Furthermore, a film of the synthesized composite was cast on ITO coated glass by the spin coating technique for potentiometric sensing and the recovery of adsorbed Pb²⁺ ions from natural and artificial water solutions. Under optimum conditions of ∼pH = 7.0 and a temperature of 25 °C, the electrode exhibited potential responses for Pb²⁺ ions in concentrations ranging from 1.0 × 10^-6 M to 1 × 10^-3 M along with a sensitivity of 0.2379 mV μM^-1 cm^-2, response time of 40 s, recovery time of 10 s, and stability for 64 days. The adsorbed Pb²⁺ ions were recovered at a rate of 84% after applying an optimized reverse voltage on the above-used electrodes. The adsorption and desorption mechanism has been explained based on the induced potential due to the electrochemical surface interaction between Pb²⁺ and the NiO-in-CHIT-g-PANI based electrode. The analytical application of the fabricated electrode in the real sample was also explored for the sensing and recovery of the respective metal ions in wastewater samples along with the possibility of optimization of the required metal concentrations.

Polypyrrole-Wrapped Carbon Nanotube Composite Films Coated on Diazonium-Modified Flexible ITO Sheets for the Electroanalysis of Heavy Metal Ions

Highly sensitive multicomponent materials designed for the recognition of hazardous compounds request control over interfacial chemistry. The latter is a key parameter in the construction of the sensing (macro) molecular architectures. In this work, multi-walled carbon nanotubes (CNTs) were deposited on diazonium-modified, flexible indium tin oxide (ITO) electrodes prior to the electropolymerization of pyrrole. This three-step process, including diazonium electroreduction, the deposition of CNTs and electropolymerization, provided adhesively-bonded, polypyrrole-wrapped CNT composite coatings on aminophenyl-modified flexible ITO sheets. The aminophenyl (AP) groups were attached to ITO by electroreduction of the in-situ generated aminobenzenediazonium compound in aqueous, acidic medium. For the first time, polypyrrole (PPy) was electrodeposited in the presence of both benzenesulfonic acid (dopant) and ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA), which acts as a chelator. The flexible electrodes were characterized by XPS, Raman and scanning electron microscopy (SEM), which provided strong supporting evidence for the wrapping of CNTs by the electrodeposited PPy. Indeed, the CNT average diameter increased from 18 ± 2.6 nm to 27 ± 4.8, 35.6 ± 5.9 and 175 ± 20.1 after 1, 5 and 10 of electropolymerization of pyrrole, respectively. The PPy/CNT/NH₂-ITO films generated by this strategy exhibit significantly improved stability and higher conductivity compared to a similar PPy coating without any embedded CNTs, as assessed by from electrochemical impedance spectroscopy measurements. The potentiometric response was linear in the 10⁻⁸–3 × 10⁻⁷ mol L⁻¹ Pb(II) concentration range, and the detection limit was 2.9 × 10⁻⁹ mol L⁻¹ at S/N = 3. The EGTA was found to drastically improve selectivity for Pb(II) over Cu(II). To account for this improvement, the density functional theory (DFT) was employed to calculate the EGTA–metal ion interaction energy, which was found to be −374.6 and −116.4 kJ/mol for Pb(II) and Cu(II), respectively, considering solvation effects. This work demonstrates the power of a subtle combination of diazonium coupling agent, CNTs, chelators and conductive polymers to design high-performance electrochemical sensors for environmental applications.

Direct detection of potassium and lead (II) ions based on assembly-disassembly of a chiral cyanine dye /TBA complex

A highly selective and sensitive direct detection of potassium (K⁺) and lead (Pb²⁺) ions was developed by using the assembly and disassembly of a chiral cyanine dye/TBA complex. The dye DMSB (3-ethyl-2-[3-(3-ethyl-3H-benzoselenazol-2-ylidene)-2-methylprop-1-enyl] benzoselenazolium bromide) loses the ability of self-assembly, but it can be activated by thrombin-binding aptamer (TBA) G-quadruplex structure. And only the TBA G-quadruplex formed in the presence of K⁺, can strongly induce J-aggregate signals of DMSB. Because the Pb²⁺ ions can bind and stabilize the TBA G-quadruplex with much higher efficiency than K⁺, the J-aggregate signals of DMSB falls sharply when the Pb²⁺ is present. As a result, the assembly and disassembly of DMSB allows the selective detection of 10 μM K⁺ and 20 nM Pb²⁺ respectively, even the competitive sodium ion (Na⁺) was as high as 145 mM. The linear correlation existed between the J-aggregate intensity and the concentration of K⁺ and Pb²⁺ over the range of 0.5-5.0 mM and 200-2000 nM, respectively. Moreover, the concentration of K⁺ (∼3 mM) and Pb²⁺ (below 20 nM) in human blood serum samples were determined by the present method, which agreed well with inductively coupled plasma mass spectrometry (ICP-MS). This work not only opens a door for the further development of G-quadruplex-based aptasensor in complex real system, but also provides a simple and versatile sensing platform for ion detection in clinic.

A multi-functional minimally-disruptive portable electrochemical system based on yeast/Co3O4/Au/SPEs for blood lead (II) measurement

A minimally-disruptive portable electrochemical system is constructed by combining a hand-held syringe as reservoir with disposable screen-printed electrodes (SPEs) modified with a simple and efficient yeast/Co₃O₄/Au material for lead determination by a square-wave voltammetry (SWV) method. Not only can it preserve the operation and advantages of the conventional electrochemical procedure, but it also integrates sampling, filtering and analysis to make the determination of lead convenient and effective at higher and lower concentration levels. This is the first report of a microbial biosensor based on active yeast crosslinked to Co₃O₄/Au particles using glutaraldehyde as the crosslinking agent. The determination process is simplified by introducing a fiber filter and takes only 150 s with the developed system, which illustrates its simplicity, speed and detection accuracy. Also, the design shows a wide log-linear dynamic range (LDR) from 10^-8 to 10^-14 g·L^-1, with a limit of detection (LOD) of 3.45 × 10^-15 g·L^-1 (S/N = 3). Additionally, the proposed system was used to determine lead in blood samples, which demonstrated the potential of this biosensor for use in practical applications. Furthermore, this study provides a basis for the development of microscale blood devices for lead measurement.