Critical reviews of electro-reactivity of screen-printed nanocomposite electrode to safeguard the environment from trace metals

Development of pectin-based gel electrolyte for wireless electrochemical determination of cadmium and lead using smartphone

A portable device offering effortlessness, mobility, and affordability for real-time and on-site monitoring of heavy metals is currently in great demand to maintain environmental sustainability. Herein, a platform utilizing a biopolymeric gel-based electrolyte for the on-field simultaneous determination of Cd(II) and Pb(II) is described. Pectin, a natural polymer, was exploited as a chemical delivery medium on account of its biodegradability, environmental friendliness, and rapid dissolving characteristics. The gel electrolyte was prepared by having pectin dissolved in KCl mixed with Sb(III)-Bi(III) bimetallic alloy solution, and casted onto a paper substrate. An in situ bimetallic alloy and pre-mixed bismuth nanoparticles modified screen-printed graphene electrode (Sb-Bi/BiNP/SPGE) were employed to enhance the electrochemical signals of Cd(II) and Pb(II) for the differential pulse anodic stripping voltammetry (DPASV). It was demonstrated that the platform was capable of generating sharp and well-defined current signals, achieving the low detection limits of 50.98 ng mL-1 for Cd(II) and 40.80 ng mL-1 for Pb(II). The reproducibility, as indicated by the relative standard deviation, was found to be less than 10.4 % (n = 10) for the developed gel-based device when coupled with a wireless near field communication (NFC) potentiostat. Lastly, the obtained sensor was applied for quantification of Cd and Pb in potentially contaminated groundwater samples. The recoveries obtained were satisfactorily within the acceptable range. The newly designed platform exhibited several advantages, including small sample volume (μL), low-cost, no sample preparation requirements, and being environmentally friendly. The convenience of a portable device utilizing the proposed biopolymeric gel-based electrolyte for on-field analysis makes it highly appealing for various applications.

Thiol-based chemically modified carbon screen-printed electrode for simultaneous quantification of trace level Pb(II) and Cd(II)

Present work reports, the development of a novel electrochemical sensor based on a diazonium-coupling reaction and covalent attachment of the -NH2 group of cysteamine (Cyst) on screen-printed carbon electrode (SPCE), for simultaneous determination of Pb(II) and Cd(II). Initially, the in-situ generated 4-carboxyphenyl (4-CP) diazonium salt was electro-grafted to generate 4-CP/SPCE, followed by covalent bonding of terminal carboxylic group of 4-CP with -NH2 group of Cyst to give Cyst/4-CP/SPCE. The modified electrode showed an enhanced selectivity and sensitivity toward the quantification of Pb(II) and Cd(II) using square wave anodic stripping voltammetry (SWASV) without mutual interference. Under optimal experimental conditions, the newly designed sensor showed a wide linear range of 0.01 µM to 0.7 µM. The limit of detection (LOD) obtained was 0.882 nM (0.09 ppb) and 0.65 nM (0.134 ppb) for Cd(II) and Pb(II), respectively. The modified SPCE exhibited good stability, selectivity, and reproducibility. Furthermore, the sensor was successfully applied for the determination of Pb(II) and Cd(II) ions in water samples which illustrated excellent recoveries in different spiked samples and the results were in line with the standard ICP-AES analysis.

Emerging Trends in nanostructured materials-coated screen printed electrodes for the electrochemical detection of hazardous heavy metals in environmental matrices

Heavy metal ions (HMIs) have become a significant contaminant in recent years. The increase in heavy metal pollution is a serious situation, requiring progressively robust, fast sensing, highly sensitive, and suitable techniques for heavy metal detection. Compared to other classical analytical methods, electroanalytical techniques, especially stripping voltammetric techniques with modified screen-printed electrodes (SPEs), have several advantages, such as fast sensing, great sensitivity, specificity, and long-time stability. Therefore, these techniques are more suitable for HMI detection. In this review, the nanostructured materials used to coat SPEs for the electrochemical determination of HMI are summarized. Additionally, the electrode fabrication method, modification steps, and electroanalytical study of these materials are systematically discussed. Hence, this review will support the researchers in precisely evaluating the electrochemical HMIs detection through highly sensitive stripping voltammetric techniques using SPE modified with nanostructured carbon and their allotropes, metal, metal oxides and their nanocomposites as sensor materials. Moreover, modified electrodes real time detection of HMIs in different food and environmental samples were briefly discussed.

Progress and prospects in flexible tactile sensors

Flexible tactile sensors have the advantages of large deformation detection, high fault tolerance, and excellent conformability, which enable conformal integration onto the complex surface of human skin for long-term bio-signal monitoring. The breakthrough of flexible tactile sensors rather than conventional tactile sensors greatly expanded application scenarios. Flexible tactile sensors are applied in fields including not only intelligent wearable devices for gaming but also electronic skins, disease diagnosis devices, health monitoring devices, intelligent neck pillows, and intelligent massage devices in the medical field; intelligent bracelets and metaverse gloves in the consumer field; as well as even brain-computer interfaces. Therefore, it is necessary to provide an overview of the current technological level and future development of flexible tactile sensors to ease and expedite their deployment and to make the critical transition from the laboratory to the market. This paper discusses the materials and preparation technologies of flexible tactile sensors, summarizing various applications in human signal monitoring, robotic tactile sensing, and human-machine interaction. Finally, the current challenges on flexible tactile sensors are also briefly discussed, providing some prospects for future directions.

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.

Environmental monitoring of trace metal pollutants using cellulosic-paper incorporating color change of azo-chromophore

An essential requirement for colorimetric paper-sensor is to allow the target analytes (heavy metal ions) to access the chromophore while maintaining strong chromophore immobilization on the porous substrate surface. This work evaluates the selection of sensitive chromophores (dithizone, 1-(2-pyridylazo) 2-naphthol and 4-(2-pyridylazo)-resorcinol) and their immobilization strategies on paper sensors. Dithizone (DTz) are capable of producing a significant color transition at unadjusted pH, observed by UV-Vis absorption spectroscopy and visible recognition. After immobilizing DTz on a paper substrate (cellulose acetate/chitosan substrate), the DTz-paper sensor showed a distinctive color change from blue-green to peach-pink upon reaction with Pb²⁺ ions, and the color intensity was proportional to the metal concentration. Quantitative analysis using RGB (R:Red; G:Green; B:Blue) plots showed that increasing DTz concentration on the CA/CS paper sensor increases the difference in total color intensity (∆I_T) and the difference in red code intensity (∆I_R). This is due to the formation of more DTz-Pb²⁺ complexes on the CA/CS paper substrate. The CA/CS paper strips immobilized with 100 ppm DTz showed practical potential for rapid detection of heavy metal ions. The DTz-CA/CS paper sensor showed significant color change when detecting spiked heavy metals ions (0.1 ppm Pb²⁺, 2.0 ppm Zn²⁺, and 0.2 ppm Cu²⁺) in river water samples that prepared at the maximum permissible limit for industrial effluent in Malaysia.

Sustainable Downscaled Catalytic Colorimetric Determination of Manganese in Freshwater Using Smartphone-Based Monitoring Oxidation of 3,3′,5,5′-Tetramethylbenzidine by Periodate

A sustainable downscaled procedure using smartphone-based colorimetric determination of manganese (Mn(II)) was developed. This novel Mn(II) determination procedure is proposed using a simple, available microwell-plate platform and a smartphone as a detector. This approach is based on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by periodate using Mn(II) as a catalyst. The catalytic kinetics of Mn(II) under different conditions was investigated to determine the optimum condition where the different catalytic activities of various concentrations of Mn(II) evince. Under the optimum condition, the bluish-green product of oxidized TMB, proportioned to the concentration of Mn(II), was monitored using a smartphone camera, and the color signals were processed using ImageJ Software. The developed procedure showed great selectivity and sensitivity as linearity ranged from 1.8 × 10⁻⁶ to 4.6 × 10⁻⁵ M (0.1 to 2.5 μg/mL). The limits of detection and quantitation were 3.6 × 10⁻⁶ and 1.1 × 10⁻⁵ M (0.2 and 0.6 μg/mL), respectively. The determination of Mn(II) in freshwater samples was demonstrated to assess environmental water quality as an initial model to more easily promote water management according to the United Nations Sustainable Development Goals (UN-SDGs). The intensity of the red could be successfully applied to evaluate Mn(II) in canals and river water with no significant differences compared with the reference method of Inductively Coupled Plasma Optical Emission Spectrometry at a confidence level of 95%.