Electrochemical biosensors combine the sensitivity of electroanalytical methods with the inherent bioselectivity of the biological component. The biological component in the sensor recognizes its analyte resulting in a catalytic or binding event that ultimately produces an electrical signal monitored by a transducer that is proportional to analyte concentration. Some of these sensor devices have reached the commercial stage and are routinely used in clinical, environmental, industrial, and agricultural applications. The two classes of electrochemical biosensors, biocatalytic devices and affinity sensors, will be discussed in this critical review to provide an accessible introduction to electrochemical biosensors for any scientist (110 references).

The world of sensors is diverse and is advancing at a rapid pace due to the fact of its high demand and constant technological improvements. Electrochemical sensors provide a low-cost and convenient solution for the detection of variable analytes and are widely utilized in agriculture, food, and oil industries as well as in environmental and biomedical applications. The popularity of electrochemical sensing stems from two main advantages: the variability of the reporting signals, such as the voltage, current, overall power output, or electrochemical impedance, and the low theoretical detection limits that originate from the differences in the Faradaic and nonFaradaic currents. This review article attempts to cover the latest advances and applications of electrochemical sensors in different industries. The role of nanomaterials in electrochemical sensor research and advancements is also examined. We believe the information presented here will encourage further efforts on the understanding and progress of electrochemical sensors.

The response of ion-selective membrane electrodes is usually still described with the semiempirical Nicolskii-Eisenman equation although it cannot correctly reproduce experimental data if ions of different charges are involved. The recently published self-consistent model that was derived for two ions of any charges is now extended to any number of ions of any charge. One single explicit equation is here given for the first time for any number of monovalent, divalent, and trivalent ions. Deviations relative to the Nicolskii-Eisenman equation are shown to be especially high at low interferences and bias calibrations if done in a mixed solution of a target sample as well as multivariate calibrations with sensor arrays.

Over the past decade, the development of amperometric sensors and biosensors using microfabrication techniques has gained considerable attention. This interdisciplinary approach aims at bringing together scientific fields such as: chemistry, physics, engineering and biology to achieve devices’ miniaturization, integration and automatization. Among the technologies that have been reviewed for the fabrication of the microelectrodes, the most common are: soft lithography and microfabrication techniques, such as physical vapor deposition of different metals, photolithography, chemical wet etching method and anodic bonding process. The required parameters in the design of a microfabricated electrode array, such as inter-electrode distance, the three-electrode system, and the role of each electrode have been intensively discussed. This review provides an overview about the state-of-the-art microfabrication devices and their applications, as well as the recent advances in the fabrication of microelectrodes as transducers for amperometric sensors, immunosensors and biosensors with various applications in environmental, biomedical and pharmaceutical fields.

在分析研究国内外海洋底水原位探测技术的前提下，详细阐述了自主研发的“海水溶解气甲烷原位探测技术成果”的研发思路、关键技术和与国外技术的区别；结合该技术在我国南海北部水合物赋存区获得海洋底水原位甲烷测试数据以及现有分层海水技术在南海北部表层海水和台西南盆地底层海水中甲烷测试数据，进行了水合物勘探中分层海水甲烷指标地球化学特征和不同海水测量方法技术在天然气水合物勘探中指示作用的研究和评价，旨在为天然气水合物中海水地球化学勘探方法的选择和发展方向提供参考依据。结果表明：(1)表层海水溶解气甲烷异常在区域水合物远景区中具有10~50 nmol·L^-1的绝对甲烷浓度和面积较大(上千km²)的区域地球化学特征；(2)底层海水甲烷异常背景值一般具有100 nmol·L^-1以上的绝对甲烷浓度和面积较确定的局部地球化学异常特征；(3)海洋底水原位甲烷地球化学异常数据在水合物赋存区上的异常具有300~800 nmol·L^-1的绝对甲烷浓度并具有高衬度异常特征。勘探技术成果显示：(1)常规技术和CTD技术获取的表层海水异常能够筛选水合物勘探远景区；(2)底水原位技术和台湾的岩心钻探技术(core top water)获取的底水地球化学异常与地下烃类聚集体渗漏相关，并有以生物成因气为主的同位素特征，因此该异常能够显示与水合物相关的甲烷渗漏地，为水合物赋存区段的识别提供依据。海水原位地球化学勘探技术在水合物海水地球化学勘探中具有广阔的应用前景。

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

This article aims to review the different devices that are available for the in situ monitoring of analytes found in the marine environment.

Electrochemical methods are the main methods for measuring seawater pH. The self-developed electrochemical pH sensor is based on iridium metal and its oxide electrode, a method for its calibration and data correction in seawater environment was established and applied for in-situ testing in nearshore and oceanic environments. The instrument calibration includes (1)Selecting appropriate calibration buffer reagents according to the calibration requirements of seawater pH analysis; (2)Preparing calibration buffer system by replacing the commonly used 2-aminopyridine (AMP) solution with standard seawater. Data correction mainly includes temperature background correction and error correction. Insitu testing in the sea area and comparison with other similar instruments show that the error caused by the difference of calibration system can be up to 1.00 pH unit, and the data correction can improve the testing accuracy from 0.10 pH unit to 3.00 pH unit. The calibration and data correction method of the instrument can effectively improve the measurement accuracy of this self-developed pH sensor.

Dissolved oxygen is an important index to evaluate water quality, and its concentration is of great significance in industrial production, environmental monitoring, aquaculture, food production, and other fields. As its change is a continuous dynamic process, the dissolved oxygen concentration needs to be accurately measured in real time. In this paper, the principles, main applications, advantages, and disadvantages of iodometric titration, electrochemical detection, and optical detection, which are commonly used dissolved oxygen detection methods, are systematically analyzed and summarized. The detection mechanisms and materials of electrochemical and optical detection methods are examined and reviewed. Because external environmental factors readily cause interferences in dissolved oxygen detection, the traditional detection methods cannot adequately meet the accuracy, real-time, stability, and other measurement requirements; thus, it is urgent to use intelligent methods to make up for these deficiencies. This paper studies the application of intelligent technology in intelligent signal transfer processing, digital signal processing, and the real-time dynamic adaptive compensation and correction of dissolved oxygen sensors. The combined application of optical detection technology, new fluorescence-sensitive materials, and intelligent technology is the focus of future research on dissolved oxygen sensors.

This study utilized tetramethylammonium hydroxide (TMAH) as a substitute for traditional catalysts and successfully incorporated platinum octaethylporphyrin (PtOEP) into SiO2 nanoparticles (PtOEP@SiO2) via the Stöber method. Methyl silicone resin was employed as the matrix material, and a drop-coating technique was applied to fabricate thin films of PtOEP@SiO2 particles for dissolved oxygen (DO) sensing in seawater. By optimizing the concentrations of TMAH and PtOEP, a highly sensitive oxygen-sensing film with a quenching ratio (I0/I100) of 28 was ultimately developed, with a wide linear detection range (0~20 mg/L, R2 = 0.994). Stability tests revealed no significant performance degradation during five oxygen–nitrogen cycle tests. After 30 days of immersion in East China Sea seawater, the quenching ratio decreased by only 6%, confirming its long-term stability and excellent resistance to ion interference. This research provides a novel strategy for developing highly reliable in situ marine DO sensors.

A new submersible probe for the in situ detection of nitrate, nitrite, and chloride in seawater is presented. Inline coupling of a desalination unit, an acidification unit, and a sensing flow cell containing all-solid-state membrane electrodes allows for the potentiometric detection of nitrate and nitrite after removal of the key interfering ions in seawater, chloride and hydroxide. Thus, the electrodes exhibited attractive analytical performances for the potentiometric detection of nitrate and nitrite in desalinated and acidified seawater: fast response time (t< 12 s), excellent stability (long-term drifts of <0.5 mV h), good reproducibility (calibration parameter deviation of <3%), and satisfactory accuracy (uncertainties <8%Diff compared to reference technique). The desalination cell, which can be repetitively used for about 30 times, may additionally be used as an exhaustive, and therefore calibration-free, electrochemical sensor for chloride and indirect salinity detection. The detection of these two parameters together with nitrate and nitrite may be useful for the correlation of relative changes in macronutrient levels with salinity cycles, which is of special interest in recessed coastal water bodies. The system is capable of autonomous operation during deployment, with routines for repetitive measurements (every 2 h), data storage and management, and computer visualization of the data in real time. In situ temporal profiles observed in the Arcachon Bay (France) showed valuable environmental information concerning tide-dependent cycles of nitrate and chloride levels in the lagoon, which are here observed for the first time using direct in situ measurements. The submersible probe based on membrane electrodes presented herein may facilitate the study of biogeochemical processes occurring in marine ecosystems by the direct monitoring of nitrate and nitrite levels, which are key chemical targets in coastal waters.

The health and integrity of our water sources are vital for the existence of all forms of life. However, with the growth in population and anthropogenic activities, the quality of water is being impacted globally, particularly due to a widespread problem of nitrate contamination that poses numerous health risks. To address this issue, investigations into various detection methods for the development of in situ real-time monitoring devices have attracted the attention of many researchers. Among the most prominent detection methods are chromatography, colorimetry, electrochemistry, and spectroscopy. While all these methods have their pros and cons, electrochemical and optical methods have emerged as robust and efficient techniques that offer cost-effective, accurate, sensitive, and reliable measurements. This review provides an overview of techniques that are ideal for field-deployable nitrate sensing applications, with an emphasis on electrochemical and optical detection methods. It discusses the underlying principles, recent advances, and various measurement techniques. Additionally, the review explores the current developments in real-time nitrate sensors and discusses the challenges of real-time implementation.

The exploration of the ocean is essential for the exploitation of marine resources and the sustainable development of human society. In order to assess both the health and the resources of the marine environment, a variety of chemical and biological sampling is needed. Traditionally, marine samples are collected on site and transported to a laboratory for analysis. Analytical methods are often tedious, and it is difficult to know the in situ real-time status. This review provides a comprehensive summary of the development of in situ chemical and biological sensors for the typical compounds in the ocean, including methane, radon, ferrous ion, carbon dioxide, microorganisms, pollutants, nutrients and seafood. Different types of sensors for each compound are highlighted, such as novel electrochemical and optical sensors. Commercial status of different sensors is introduced, and performance of representative sensors is compared and discussed deeply. The advantages and disadvantages of each sensing technique are analyzed and evaluated in detail. Finally, future prospects and work directions are presented, such as the deployment of these in situ sensors on fixed and/or moving platforms, development of microfluidic sensors and exploration of new antifouling materials and methods. This paper could serve as a resource for developing more advanced in situ chemical sensors and biosensors for marine scientific research, as well as related practical applications for monitoring marine resource exploration and exploitation and for environmental protection.

Determination of silicate concentration in seawater without addition of liquid reagents was the key prerequisite for developing an autonomous in situ electrochemical silicate sensor (Lacombe et al., 2007) [11]. The present challenge is to address the issue of calibrationless determination. To achieve such an objective, we chose chronoamperometry performed successively on planar microelectrode (ME) and ultramicroelectrode (UME) among the various possibilities. This analytical method allows estimating simultaneously the diffusion coefficient and the concentration of the studied species. Results obtained with ferrocyanide are in excellent agreement with values of the imposed concentration and diffusion coefficient found in the literature. For the silicate reagentless method, successive chronoamperometric measurements have been performed using a pair of gold disk electrodes for both UME and ME. Our calibrationless method was tested with different concentrations of silicate in artificial seawater from 55 to 140×10(-6) mol L(-1). The average value obtained for the diffusion coefficient of the silicomolybdic complex is 2.2±0.4×10(-6) cm(2) s(-1), consistent with diffusion coefficient values of molecules in liquid media. Good results were observed when comparing known concentration of silicate with experimentally derived ones. Further work is underway to explore silicate determination within the lower range of oceanic silicate concentration, down to 0.1×10(-6) mol L(-1).Copyright © 2012 Elsevier B.V. All rights reserved.

A Square Wave Voltammetry electrochemical method is proposed to measure phosphate in seawater as pulse techniques offer a higher sensitivity as compared to classical cyclic voltammetry. Chronoamperometry cannot be either adapted for an in situ sensor since this method requires to have controlled convection which will be impossible in a miniaturised sensor. Tests and validation of Square Wave Voltammetry parameters have been performed using an open cell and for the first time with a small volume (<400µL) laboratory prototypes. Two designs of prototypes have been compared. Using high frequency (f=250Hz) allows to obtain a linear behaviour between 0.1 and 1µmolL(-1) with a very low limit of detection of 0.05 µmolL(-1) after 60min of complexation waiting time. In order to obtain a linear regression for a larger concentration range i.e. 0.25-4µmolL(-1), a lower frequency of 2.5Hz is needed. A limit of detection of 0.1µmolL(-1) is obtained in this case after 30min of complexation waiting time for the peak measured at E=0.12V. Changing the position of the molybdenum electrode for the complexation step and moving the detection into another electrochemical cell allow to decrease the reaction time down to 5min. Copyright © 2016 Elsevier B.V. All rights reserved.

Heavy metal ions (HMIs) are very harmful to the ecosystem when they are present in excess of the recommended limits. They are carcinogenic in nature and can cause serious health issues. So, it is important to detect the metal ions quickly and accurately. The metal ions arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg) are considered to be very toxic among other metal ions. Standard analytical methods like atomic absorption spectroscopy, atomic fluorescence spectroscopy, and X-ray fluorescence spectroscopy are used to detect HMIs. But these methods necessitate highly technical equipment and lengthy procedures with skilled personnel. So, electrochemical sensing methods are considered to be more advantageous because of their quick analysis with precision and simplicity to operate. They can detect a wide range of heavy metals providing real-time monitoring and are cost-effective and enable multiparametric detection. Various sensing applications necessitate severe regulation regarding the modification of electrode surfaces. Numerous nanomaterials such as graphene, carbon nanotubes, and metal nanoparticles have been extensively explored as interface materials in electrode modifiers. These nanoparticles offer excellent electrical conductivity, distinctive catalytic properties, and high surface area resulting in enhanced electrochemical performance. This review examines different HMI detection methods in an aqueous medium by an electrochemical sensing approach and studies the recent developments in interface materials for altering the electrodes.© 2024 The Authors. Published by American Chemical Society.

Excessive levels of Pb2+ and Cd2+ in seawater pose significant combined toxicity to marine organisms, resulting in harmful effects and further threatening human health through biomagnification in the food chain. Traditional methods for detecting marine Pb2+ and Cd2+ rely on laboratory analyses, which are hindered by limitations such as sample degradation during transport and complex operational procedures. In this study, we present an electrochemical sensor based on intelligent mobile detection devices. By combining G-COOH-MWCNTs/ZnO with differential pulse voltammetry, the sensor enables the efficient, simultaneous detection of Pb2+ and Cd2+ in seawater. The G-COOH-MWCNTs/ZnO composite film is prepared via drop-coating and is applied to a glassy carbon electrode. The film is characterized using cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy, while Pb2+ and Cd2+ are quantified using differential pulse voltammetry. Using a 0.1 mol/L sodium acetate buffer (pH 5.5), a deposition potential of −1.1 V, and an accumulation time of 300 s, a strong linear correlation was observed between the peak response currents of Pb2+ and Cd2+ and their concentrations in the range of 25–450 µg/L. The detection limits were 0.535 µg/L for Pb2+ and 0.354 µg/L for Cd2+. The sensor was applied for the analysis of seawater samples from Maowei Sea, achieving recovery rates for Pb2+ ranging from 97.7% to 103%, and for Cd2+ from 97% to 106.1%. These results demonstrate that the sensor exhibits high sensitivity and stability, offering a reliable solution for the on-site monitoring of heavy metal contamination in marine environments.

微电极技术在测量不稳定沉积物化学中具有不可替代的作用，日益受到重视。综合论述了目前实际应用于定量沉积物化学的三大电化学类型的微电极，覆盖了pH微电极、pCO₂微电极、硫化物微电极、溶解氧膜微电极、汞金伏安微电极的工作原理、制作方法和应用文献。特别介绍了实验室制作氧化铱pH微电极的方法和性能，描述了制作汞金伏安微电极的详细步骤及其在测量沉积物氧化还原化学成分的具体实验装置和技术方法，认为微电极技术的引入对深化沉积物生物地球化学过程研究具有重要作用。

Direct current electrical experiments with electrode arrays deployed by a submersible (ALVIN) were used to determine the resistivity structure of the seafloor below, and vertical potential gradients in sea water above, the hydrothermally active TAG mound. Apparent resistivities of the sulfides at shallow depths (∼10 m) below seafloor over the mound ranged between 0.18–0.21 ohm‐m, compared to nearby basalt pillow apparent resistivities of 2.1–2.4 ohm‐m. The potential differences between heights of about 18 to 27 m above the mound averaged +3.7 mV (voltage increasing with height), with variations between about −2.9 and +12.7 mV.

Underwater implosion experiments were conducted with thin-wall glass spheres to determine the influence that structural failure has on the pressure pulse. Four experiments were conducted with glass spheres having an outside diameter of 7.62cm, thickness of 0.762mm, and an estimated buckling pressure of 7.57MPa. The experiments were performed in a pressure vessel at a hydrostatic pressure of 6.996MPa. The average peak pressure of the implosion pressure pulse was 26.1MPa, measured at a radial distance of 10.16cm from the sphere center. A computational fluid structure interaction model was developed to assess how the failure rate of the glass structure influences the pressure time history. The model employed a specified glass failure sequence that is uniform in time and space. It was found that for the conditions of the test, a glass failure rate of 275m∕s provided a reasonable representation of the test data. The test data and the model results show that the failure time history of the structure has a significant influence on an implosion pressure pulse. Computational prediction of an implosion pressure pulse needs to include the failure time history of the structure; otherwise it will overpredict the pressure time history.

The reference electrode's performance is essential for ensuring the accuracy of electrochemical sensors in marine environments. Yet, the many existing reference electrodes can exhibit sensitivity to salinity variations, potentially leading to inaccuracies in the measurement process. Herein, we have designed a reliable solid-state reference electrode by introducing SiO-stabilized 1-methyl-3-octylimidazolium bis(trifluoromethyl sulfonyl)imide ([Cmim] [Ntf]) into a P(VdF--HFP) matrix with a SPEEK/[Cmim] [Ntf] coated Ag/AgCl as substrate. The SPEEK/[Cmim] [Ntf] coating protects the AgCl substrate, and the incorporation of SiO improves the compatibility of the IL with the polymer matrix, thereby increasing the electrode's resistance to interference and extending its long-term stability and lifespan. The developed reference electrode showed a stable and rapid response, with potential variations of less than 0.7 mV across various salinity solutions, including practical seawater, lake water, and their mixture samples. During extended periods of 18 days in deionized water and artificial seawater, the electrode demonstrated negligible potential drifts of 0.36 and 0.14 mV/d, respectively. Notably, the electrode could maintain a stable potential even after being stored in a preservative solution for 67 days. Furthermore, the electrode showed a stable response to withstand pressures of up to 100 MPa, covering the vast majority of the seafloor. This innovative reference electrode is capable of maintaining a stable reference potential across various salinities, ionic strength, and full ocean depth, making it versatile for use in diverse aquatic environments, underscoring its significant potential for advancing oceanographic research and enabling new insights into the unexplored depths of oceans.

This study focuses on seafloor methane seep sites and their distribution in the northwestern part of the German North Sea. Methane seepage is a common phenomenon along marine shelves and known to occur in the North Sea, but proof of their existence was lacking in the study area. Using a ship-based multibeam echosounder we detected a minimum of 166 flares that are indicative for free gas releases from the seafloor in the German “Entenschnabel” area, which are not related to morphologic expressions at the seafloor. However, a group of small depressions was detected lacking water column anomalies but with indications of dissolved fluid release. Spatial analysis revealed that flares were not randomly distributed but show a relation to locations of subsurface salt diapirs. More than 60% of all flares were found in the vicinity of the salt diapir “Berta”. Dissolved methane concentrations of ∼100 nM in bottom waters were ten times the background value in the “Entenschnabel” area (CH4&lt; 10 nM), supporting the finding of enhanced seepage activity in this part of our study area. Furthermore, locations of flares were often related to acoustic blanking and high amplitude reflections in sediment profiler echograms, most prominently observed at location Berta. These hydroacoustic signatures are interpreted to result from increased free gas concentrations in the sediments. Electromagnetic seabed mapping depicts local sediment conductivity anomalies below a flare cluster at Berta, which can be explained by small amounts of free gas in the sediment. In our area of interest, ten abandoned well sites were included in our mapping campaign, but flare observations were spatially not related to these wells. Naturally seeping methane is presumably transported to the seafloor along sub-vertical faults, which have formed concurrently to the updoming salt. Due to the shallow water depths of 30 to 50 m in the study area, flares were observed to reach close to the sea surface and a slight oversaturation of surface waters with methane in the flare-rich northeastern part of the working area indicates that part of the released methane through seepage may contribute to the atmospheric inventory.