A miniaturized bismuth-based sensor to evaluate the marine organism Styela plicata bioremediation capacity toward heavy metal polluted seawater

Passivation strategies for enhancing sensitivity and repeatability of microelectrode electrochemical sensors

The sensitivity and repeatability are crucial for the practical application of electrochemical sensors. Many studies have focused on sensing materials and electrode structure to enhance sensitivity and repeatability rather than insulating layers. In this paper, polyaniline (PANI) microelectrode arrays were prepared to explore the influence of the insulating layer on sensitivity and repeatability of electrochemical sensors. The effects of different types of insulating layers, the sizes of the electrodes, and the thicknesses of the insulating layers were studied by experiment and simulation. The research findings indicated that the kind of organic insulating layers (Polyimide (PI) and SU-8) did not have a significant effect on the performance of the sensors. However, as the electrode area increased, the PANI film deposited on the electrode exhibited improved uniformity and density, leading to significant improvements in sensitivity and repeatability of the sensors. Additionally, the thickness of the insulating layer also had a significant impact on the performance of the device. The microelectrode with thinner insulating layers exhibited improved performance in sensitivity, repeatability and signal-to-noise ratio. The research findings indicated that increasing the electrode size and reducing the thickness of the insulating layer led to a more uniform and dense PANI film, resulting in an array electrode that exhibits excellent performance and remarkable repeatability.

Double-side effect of B/C ratio on BDD electrode detection for heavy metal ion in water

BDD (Boron-doped Diamond) electrode may hold a promising application to detect heavy metal ions for actual water monitoring and early warning, but a poor understanding of influence mechanism of B/C ratio on detection performance is in the way of its fabrication and application. This work is intended to reveal the double-side effect of B/C ratio on detection performance of BDD electrode so as to facilitate its actual application. SBDD (Self-supported Boron-doped Diamond) electrode is introduced for the first time to get rid of the interference factors such as substrate. A systematic investigation is conducted for the influence of B/C ratio on microstructure and electrochemical behavior of SBDD electrodes. With the increase of B/C ratio, the grain size continuously increases, and the preferred orientation gradually changes from plane (220) to (111). The gradual increasing of impurity phase content indicates a deterioration of diamond phase quality. In addition, the electrode electrochemical behavior initially gets better then worse. SBDD electrode with a B/C ratio of 1/500 has the largest active surface area of 2.1 cm², the smallest diffusion resistance and the highest signal response. Under optimal parameter set, the SBDD electrode enjoys a sensitivity of 0.42 μA L μg^-1 cm^-2 and a detection limit of 1.12 μg L^-1 in a wide linear range of 5-120 ppb. The phase quality and grain morphology jointly contribute to the double-side effect. A suitable B-sp³-C content, preferred orientation of (111) and small particle size may make the performance improvement of BDD electrode available.

Biomonitoring of Heavy Metals: The Unexplored Role of Marine Sessile Taxa

Coastal areas are known to receive significant anthropogenic inputs, mainly deriving from metropolitan areas, industries, and activities related to tourism. Among these inputs, some trace elements are listed as priority pollutants in the European Water Framework Directive, due to their ability to bioaccumulate in organisms. Many studies have been conducted on heavy metals (HMs) accumulation and on their possible effects on different edible marine species. While the most studied sessile organisms are bivalves, in the current review, we focus our attention on other sessile taxa (sponges, cnidarians, bryozoans, polychaetes, cirripeds, and tunicates), proposed as bioindicators in coastal shallow waters. Although their potential as bioindicator tools has been repeatedly highlighted in the literature, these organisms are still poorly investigated and considered for monitoring. In this context, we analyze the available literature about this topic, in order to summarize the current knowledge and identify possible applications of these organisms in a bioremediation scenario.

A reusable AuNPS with increased stability applied for fast screening of trace heavy metals in edible and medicinal marine products

Heavy metal pollution in marine environment poses a severe threat to the safety of marine products and is thus causing increasingly concerns in terms of their toxicity and potential health risks pose to human. Due to the complex matrix of marine products, a fast screening method for heavy metals at trace level with low price, reusability, high accuracy and long lifetime is of urgency and necessity for consumers and processing factories. This work described a simplified screening system through the preparation, characterization and particular application of Au nano particle sensor (AuNPS) in the complex marine matrix, the main aim is to significantly increase the stability, sensitivity and lifetime of detection system dedicated to Cu and Hg trace analysis in marine products. It is worth mentioning that, the proposed screening system was characterized through electrochemical experiments and theoretical calculations, which could be a new evidence for selecting the detection system in commercially complex samples. Importantly, the discipline of deposition and oxidative stripping process on AuNPS was explained based on the mechanism of Metal Ion Deficient Layer (MIDL), and illustrated with SEM changes during stripping process, as well as the dissolving-out rate of metals on AuNPS material. Moreover, to further improve the reusability and stability of AuNPS sensor, the complex marine matrix was purified by pre-plating interferences on indium tin oxide glass electrode. The screening system exhibited a liner response in the range of 0.02-0.10 μg mL^-1 for Hg, 0.01-0.10 μg mL^-1 and 0.001-0.01 μg mL^-1 for Cu with the detection limits of 0.138 mg kg^-1 and 1.51 mg kg^-1 in marine matrix, respectively. The sensitivity and lifetime was at least two times better as compared to similar works even after 20-times use. Finally, this proposed analysis system combined with purification procedure was successfully applied for the edible and medicinal marine products analysis, meanwhile, the accuracy and stability were confirmed with standard analytical methods.

Tracking metal ions with polypyrrole thin films adhesively bonded to diazonium-modified flexible ITO electrodes

Adhesively bonded polypyrrole thin films doped with benzene sulfonic acid (BSA) were electrodeposited on aminobenzenediazonium-modified flexible ITO electrodes and further employed for the detection of Pb²⁺, Cu²⁺, and Cd²⁺ metal ions in aqueous medium. The aminophenyl (AP) adhesive layer was grafted to ITO by electroreduction of the in situ generated parent diazonium compound. Polypyrrole (PPy) thin films exhibited remarkable adhesion to aminophenyl (ITO-AP). The strongly adherent polypyrrole films exhibited excellent electroactivity in the doped state with BSA which itself served to chelate the metal ions in aqueous medium. The surface of the resulting, modified flexible electrode was characterized by XPS, SEM, and electrochemical methods. The ITO-AP-PPy electrodes were then used for the simultaneous detection of Cu²⁺, Cd²⁺, and Pb²⁺ by differential pulse voltammetry (DPV). The detection limits were 11.1, 8.95, and 0.99 nM for Cu²⁺, Cd²⁺, and Pb²⁺, respectively. In addition, the modified electrodes displayed a good reproducibility, making them suitable for the determination of heavy metals in real wastewater samples.

Recent advances in conventional and contemporary methods for remediation of heavy metal-contaminated soils

Remediation of heavy metal-contaminated soils has been drawing our attention toward it for quite some time now and a need for developing new methods toward reclamation has come up as the need of the hour. Conventional methods of heavy metal-contaminated soil remediation have been in use for decades and have shown great results, but they have their own setbacks. The chemical and physical techniques when used singularly generally generate by-products (toxic sludge or pollutants) and are not cost-effective, while the biological process is very slow and time-consuming. Hence to overcome them, an amalgamation of two or more techniques is being used. In view of the facts, new methods of biosorption, nanoremediation as well as microbial fuel cell techniques have been developed, which utilize the metabolic activities of microorganisms for bioremediation purpose. These are cost-effective and efficient methods of remediation, which are now becoming an integral part of all environmental and bioresource technology. In this contribution, we have highlighted various augmentations in physical, chemical, and biological methods for the remediation of heavy metal-contaminated soils, weighing up their pros and cons. Further, we have discussed the amalgamation of the above techniques such as physiochemical and physiobiological methods with recent literature for the removal of heavy metals from the contaminated soils. These combinations have showed synergetic effects with a many fold increase in removal efficiency of heavy metals along with economic feasibility.

Screen-Printed Electrodes Modified with "Green" Metals for Electrochemical Stripping Analysis of Toxic Elements

This work reviews the field of screen-printed electrodes (SPEs) modified with “green” metals for electrochemical stripping analysis of toxic elements. Electrochemical stripping analysis has been established as a useful trace analysis technique offering many advantages compared to competing optical techniques. Although mercury has been the preferred electrode material for stripping analysis, the toxicity of mercury and the associated legal requirements in its use and disposal have prompted research towards the development of “green” metals as alternative electrode materials. When combined with the screen-printing technology, such environment-friendly metals can lead to disposable sensors for trace metal analysis with excellent operational characteristics. This review focuses on SPEs modified with Au, Bi, Sb, and Sn for stripping analysis of toxic elements. Different modification approaches (electroplating, bulk modification, use of metal precursors, microengineering techniques) are considered and representative applications are described. A developing related field, namely biosensing based on stripping analysis of metallic nanoprobe labels, is also briefly mentioned.