In Situ Preconcentration and Quantification of Cu2+ via Chelating Polymer-Wrapped Multiwalled Carbon Nanotubes

A responsive organic probe based photoelectrochemical sensor for hydrazine detection

This study developed a new photoelectrochemical (PEC) sensor for the detection of the hydrazine (N2H4, HZ) based on a donor-π-bridge-acceptor (D-π-A) configuration organic photoactive dye (Dye-HZ). The dye was covalently immobilized on an FTO/TiO2 (FTO: fluorine-doped tin oxide) substrate, resulting in a photoanode FTO/TiO2/Dye-HZ that exhibits a specific PEC response to N2H4. Hydrazine reacts with the acetyl group in the Dye-HZ molecule, leading to its removal and the formation of a hydroxy group. The hydroxy group dissociates a hydrogen ion, forming a phenoxide anion with strong electron-donating characteristics. As a result, the dye molecule exhibits a strong intramolecular charge transfer effect, significantly enhancing absorbance and photoelectric response under visible light irradiation, leading to a remarkable increase in photocurrent and enabling highly sensitive detection of hydrazine. Furthermore, the PEC sensor demonstrates excellent selectivity and can be applied for the detection of hydrazine in real water samples. This study presents an innovative PEC sensing approach for hydrazine based on responsive photoactive molecules, providing new insights for PEC detection of other environmental pollutants.

Electric field-enabled aptasensing interfacial engineering to simultaneously enhance specific preconcentration and electrochemical detection of mercury and lead ions

Aptamers with strong affinity to heavy metal ions (HMIs) allow fabrication of electrochemical sensors with high selectivity and sensitivity, while controllable regulation of aptamer-HMI recognition at the sensing interface, which is vital for better analytical performance, remains challenging. Here, an electric field-based strategy for engineering an aptasensing interface was proposed to realize the specific preconcentration and accurate detection of mercury (Hg2+) and lead (Pb2+) ions with a ratiometric electrochemical sensor. The working principle is to apply an electric field to drive HMIs to approach the aptamer and retain the orientation of the DNA structure. Anthraquinone-2-carboxylic acid (AQ)-labeled complementary DNA was designed to simultaneously bind a ferrocene (Fc)-labeled aptamer for Hg2+ and a methylene blue (MB)-labeled aptamer for Pb2+, and the sensing interface was fabricated with this presynthesized DNA structure. For preconcentration, an electric field of 3.0 V pushed HMIs to approach the aptamer and retained the orientation of DNA to favor the following recognition; for detection, the oriented DNA in 2.5 V electric field offered a stable current of AQ as a reference. In this way, currents of AQ, Fc and MB were used to produce ratiometric signals of IAQ/IFc and IAQ/IMB for Hg2+ and Pb2+, respectively. Such a strategy allowed the simultaneous detection of Hg2+ and Pb2+ within 30 min with detection limits of 0.69 pM and 0.093 pM, respectively. The aptasensor was applied for soil, water, and crayfish analysis in paddy fields. The electric field-enabled strategy offers a new way to fabricate high-performance electrochemical aptasensor for HMIs detection.

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.

Rhodamine 6G derivative for the selective copper detection and remediation using nanoporous diatomaceous earth-engineered functional receptor

A rhodamine-derived receptor was synthesized and comprehensively characterized for structural confirmation. The receptor was able to distinguish the copper ions (Cu²⁺) from other competing cations. The yellow color of the receptor changed to pink upon adding Cu²⁺ ions, however, other competing cations ions were impotent towards any color variation. The UV-visible titration studies revealed the binding stoichiometry of a 1:1 ratio with a detection limit of 9.663 × 10^-8 M. Additionally, a novel idea of the work resides in the use of diatom for the practical application, where the receptor has been tethered on nanoporous diatomaceous earth microparticles (P2D) to remove Cu²⁺ ions. The results confirmed that 50 mg receptor functionalized DE could adsorb 10 mL of 1 ppm Cu²⁺ ions from water. Furthermore, a proof-of-concept device that is inexpensive, simple to operate, and continuously removes Cu²⁺ ions from water has been developed. The efficiency of the device in Cu²⁺ ion removal could be realized through the naked eye by observing the color change of P2D particles, which has excellent potential for application in remote locations where water contamination is a significant issue.

Polymer based nanocomposites: A strategic tool for detection of toxic pollutants in environmental matrices

A large fraction of population is suffering from waterborne diseases due to the contaminated drinking water. Both anthropogenic and natural sources are responsible for water contamination. Revolution in industrial and agriculture sectors along with a huge increase in human population has brought more amount of wastes like heavy metals, pesticides and antibiotics. These toxins are very harmful for human health, therefore, it is necessary to sense their presence in environment. Conventional strategies face various problems in detection and quantification of these pollutants such as expensive equipment and requirement of high maintenance with limited portability. Recently, nanostructured devices have been developed to detect environmental pollutants. Polymeric nanocomposites have been found robust, cost effective, highly efficient and accurate for sensing various environmental pollutants and this is due to their porous framework, multi-functionalities, redox properties, great conductivity, catalytic features, facile operation at room temperature and large surface area. Synergistic effects between polymeric matrix and nanomaterials are responsible for improved sensing features and environmental adaptability. This review focuses on the recent advancement in polymeric nanocomposites for sensing heavy metals, pesticides and antibiotics. The advantages, disadvantages, operating conditions and future perspectives of polymeric nanocomposites for sensing toxic pollutants have also been discussed.

Electric Field-Induced Specific Preconcentration to Enhance DNA-Based Electrochemical Sensing of Hg2+ via the Synergy of Enrichment and Self-Cleaning

Efficient preconcentration is critical for sensitive and selective electrochemical detection of metal ions, but rapid specific enrichment with depressed absorption of interfering ions at the electrode is challenging. Here, we proposed an electric field-induced specific preconcentration to boost the analytical performance of DNA-based electrochemical sensors for Hg²⁺ detection. As for such preconcentration, a positive external electric field was first used to enrich Hg²⁺ at an electrode assembled with T-rich DNA, thus boosting T-Hg²⁺-T recognitions. The following applied inverse electric field strips the nonspecifically absorbed Hg²⁺ and other interfering ions, thus depressing matrix interferences via self-cleaning. Based on this principle, we designed a portable device to realize programmable control of electric fields; a T-Hg²⁺-T recognition-based electrochemical sensor was thus fabricated as a model platform to assess the feasibility of electric field-induced preconcentration. The experimental results revealed that such a strategy decreased the time of T-Hg²⁺-T-based recognition from 60 to 20 min and led to detection with better reproducibility by depressing the influence of free Hg²⁺ as well as interfering ions. This strategy offered Hg²⁺ detection limits of 0.01 pM─three-fold better than that without preconcentration─within 22 min. The proposed preconcentration strategy offers a new way to enhance the analytical performance of sensing at the solid-liquid interface.

ACEstat: A DIY Guide to Unlocking the Potential of Integrated Circuit Potentiostats for Open-Source Electrochemical Analysis

Miniaturization of analytical instrumentation is paramount to enabling convenient in-field sensing. The recent thrust in potentiostat miniaturization for electrochemical sensing and general use has led to the development of commercial application specific integrated circuits (ASICs) that pack all the power of a benchtop instrument into one 5 mm × 5 mm chip. While the capabilities of these integrated circuits far exceed those of open-source potentiostats in the literature, the activation barrier for their implementation requires extensive electrical and software engineering expertise to overcome. In order to more rapidly bring the utility of ASIC potentiostats to researchers, we present a low size, weight, power, and cost (Low SWaP-C) Army Corps of Engineers potentiostat (ACEstat) based on the widely available ADuCM355 offered by Analog Devices. This potentiostat is a streamlined and fully programmable device that leverages industry-leading integrated hardware to perform electrochemical measurements such as cyclic voltammetry, pulse voltammetry, and electrochemical impedance spectroscopy. The ACEstat enables control over a wide range of test parameters and displays results through an intuitive, open-source graphical user interface available on mobile devices and computers. In this report, we present an approachable, do-it-yourself guide to unlocking the capabilities of this integrated circuit potentiostat by outlining the fabrication and programming details necessary to facilitate electroanalysis. Furthermore, we demonstrate the practicality of this device by detecting 2,4,6-trinitrotoluene (TNT) in water at sub-mg/L detection limits, highlighting its potential for in-field use.

A Generalized Potentiostat Adaptor for Multiplexed Electroanalysis

Electrochemical measurements over an array of electrodes may be accomplished with one of three potentiostat architectures: a single-channel device which averages the signal from a number of interconnected electrodes, a multichannel device with dedicated circuits for each electrode, or a single-channel device with a multiplexer interface to isolate the signal from specific electrodes. Of these three architectures, the use of a multiplexer interface is best suited to facilitate measurements over individual electrodes without the need for large numbers of dedicated potentiostat channels. We present a versatile strategy for the development of flexible printed circuit (FPC) electrode arrays with accompanying multiplexing hardware to interface with single-channel potentiostats. The FPC array was fabricated with 78 individually addressable 0.3 mm diameter gold working electrodes and characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, profilometry, impedance spectroscopy, and cyclic voltammetry to investigate the morphology, elemental composition, height profile, impedance characteristics, and electrochemical response, respectively. Interfacing the FPC array via a simple connector with three 32-channel ADG731 multiplexers permitted electrochemical measurements using single-channel commercial potentiostats. Voltammetric experiments were conducted to demonstrate the reliability, stability, and reproducibility of the FPC array and interfacing hardware. The combination of these devices represents an accessible hardware platform with robust, functionalizable electrodes, a simple connection interface with commercial potentiostats, and a low cost through the use of off-the-shelf components. Our reported strategy holds great promise to facilitate multiplexed electroanalysis in next-generation sensors to increase statistical sample size and multianalyte detection capabilities.