Elimination of Oxygen Interference in the Electrochemical Detection of Monochloramine, Using In Situ pH Control at Interdigitated Electrodes

In situ pH-Controlled electrochemical sensors for glucose and pH detection in calf saliva

Electrochemical biosensors have been extensively researched and employed across diverse fields from environmental monitoring to clinical diagnostics. Detecting biomarkers like saliva pH and glucose are crucial indicators of the health and well-being of animals and opens the door for development of new non-invasive calf health measurements. Herein, we introduce a highly sensitive and stable electrochemical sensor for detection of pH and glucose in artificial and calf saliva. Pristine gold electrodes were employed for pH measurement using the voltage where the minimum of the gold oxide reduction peak occurred as a pH indicator. For glucose sensing, we utilized an effective in-situ pH control method enabled by interdigitated microelectrodes (IDEs) to optimize pH for accurate detection of glucose in artificial and calf saliva. Glucose oxidase (GOx) was first immobilized onto a platinum black modified gold IDE array through an electrodeposition process, which involved a mixture of o-phenylenediamine (o-PD) and β-cyclodextrin (β-CD). The enzymatic based glucose sensor showed an exceptional sensitivity of -0.46 nA mM-1 in artificial saliva at a wide range of concentrations from 0.02 mM to 7 mM, with a LOD of 0.3 μM. Simultaneously, a sensitivity of -166 mV.pH-1 was recorded for the pH sensor within the pH range of 5-9. These multiplexed sensors successfully detected glucose and pH levels in calf saliva noninvasively, which is particularly significant for meeting the frequent and continuous monitoring requirements of biomarkers (glucose, pH) associated with Bovine respiratory disease (BRD) and diarrhoetic calves.

Multi-dimensional signals coupling of simultaneous acquisition stripping current with laser-induced breakdown spectroscopy for accurate analysis of Cd(II) in coexisting Cu(II)

BACKGROUND

Despite significant advancements in detecting Cd(II) using nanomaterials-modified sensitive interfaces, most detection methods rely solely on a single electrochemical stripping current to indicate concentration. This approach often overlooks potential inaccuracies caused by interference from coexisting ions. Therefore, establishing multi-dimensional signals that accurately reflect Cd(II) concentration in solution is crucial.

RESULTS

In this study, we developed a system integrating concentration, electrochemical stripping current, and laser-induced breakdown spectroscopy (LIBS) characteristic peak intensity through in-situ laser-induced breakdown spectroscopy and electrochemical integrated devices. By simultaneously acquiring multi-dimensional signals to dynamically track the electrochemical deposition and stripping processes, we observed that replacement reactions occur between Cu(II) and Cd(II) on the surface of Ru-doped MoS2 modified carbon paper electrodes (Ru-MoS2/CP). These reactions facilitate the oxidation of Cd(0) to Cd(II) during the stripping process, significantly increasing the currents of Cd(II). Remarkably, the ingenious design of the Ru-MoS2 sensitive interface allowed for the undisturbed deposition of Cu(II) and Cd(II) during the electrochemical deposition process. Consequently, our in-situ integrated device achieved accurate detection of Cd(II) in complex environments, boasting a detection sensitivity of 8606.5 counts μM⁻1.

SIGNIFICANCE

By coupling multi-dimensional signals from stripping current and LIBS spectra, we revealed the interference process between Cu(II) and Cd(II), providing valuable insights for accurate electrochemical analysis of heavy metal ions in complex water environments.

Continuous Monitoring of Monochloramine in Water, and Its Distinction from Free Chlorine and Dichloramine Using a Functionalized Graphene-Based Array of Chemiresistors

Monochloramine (MCA) is commonly added to drinking water as a disinfectant to prevent pathogen growth. The generation of MCA at the treatment plant requires tight control over both pH and the ratio of free chlorine (FC) to ammonia to avoid forming undesirable byproducts such as dichloramine (DCA) and trichloramine (TCA), which can impart odor and toxicity to the water. Therefore, continuous monitoring of MCA is essential to ensuring drinking water quality. Currently, standard colorimetric methods to measure MCA rely on the use of reagents and are unsuitable for online monitoring. In addition, other oxidants can interfere with MCA measurement. Here, we present a solid-state, reagent-free MCA sensing method using an array of few-layer graphene (FLG) chemiresistors. The array consists of exfoliated FLG chemiresistors functionalized with specific redox-active molecules that have differential responses to MCA, FC, and DCA over a range of concentrations. Chemometric methods were employed to separate the analytes' responses and to generate multivariate calibration for quantification. A minimum of three sensors are required in the array to maintain full functionality. The array has been demonstrated to quantify MCA in buffered and tap water as a low-cost, reagent-free approach to continuous monitoring.

Surface chemistry applications and development of immunosensors using electrochemical impedance spectroscopy: A comprehensive review

Immunosensors are promising alternatives as detection platforms for the current gold standards methods. Electrochemical immunosensors have already proven their capability for the sensitive, selective, detection of target biomarkers specific to COVID-19, varying cancers or Alzheimer's disease, etc. Among the electrochemical techniques, electrochemical impedance spectroscopy (EIS) is a highly sensitive technique which examines the impedance of an electrochemical cell over a range of frequencies. There are several important critical requirements for the construction of successful impedimetric immunosensor. The applied surface chemistry and immobilisation protocol have impact on the electroanalytical performance of the developed immunosensors. In this Review, we summarise the building blocks of immunosensors based on EIS, including self-assembly monolayers, nanomaterials, polymers, immobilisation protocols and antibody orientation.

Mixed chlorine/chloramines in disinfected water and drinking water distribution systems (DWDSs): A critical review

Mixed chlorine/chloramines are commonly occurring in real drinking water distribution systems (DWDSs) but often overlooked. This review provides a comprehensive overview of the occurrences, characteristics, analysis methods, and control strategies of mixed chlorine/chloramines in DWDSs. The characteristics of mixed chlorine/chloramine species are summarized for treated water in drinking water treatment plants (DWTPs), secondary disinfection facilities, and DWDSs where different disinfectants could be blended. The key to differentiating and quantifying mixed chlorine/chloramine species is to separate organic chloramines (OCs) from di/tri-chloramines and overcome certain interferences. The complex interactions between water matrixes and chlorine/chloramine species could accelerate pipeline corrosions, enhance emerging disinfection by-products risks, lead to off-flavors in drinking water, and induce bio-instability issues (such as nitrification, microorganism regrowth, and promotion of horizontal gene-transfers). Three promising strategies for alleviating mixed chlorine/chloramine species are recommended, which include (i) removing precursors intensively and reconditioning the treated water, (ii) combining UV irradiation to eliminate undesired chlorine/chloramines species, and (iii) strengthening monitoring, operation, and maintenance management of DWDSs. Finally, the challenges for gaining insights into the mechanisms of mixed chlorine/chloramine species conversion are discussed and promising research directions are proposed.

Electrochemical detection of chloride ions using Ag-based electrodes obtained from compact disc

In this work electrochemical sensors fabricated from compact disc material (waste or new) are used to quantify chloride ions in different types of samples. All three electrodes, working, counter, and pseudo-reference electrodes, were fabricated from the compact disc and directly used. Different parameters were studied in order to demonstrate the possibility of using this waste material for efficient and low-cost electrochemical sensors. Chloride sensing performance was evaluated using linear scan voltammetry as the detection technique. A sensitivity of 0.174 mA mM^-1 cm^-2 with a limit of detection of 20 μM and excellent selectivity against many interferents was observed. Selectivity and reproducibility tests were also carried out, showing excellent results. Sensors were also validated with real samples (drinking and sea water, milk, sweat and physiological solutions) with results comparable to conventional techniques. Our results show the applicability and suitability of these low-cost sensors, for detection of those analytes for which, silver, has high sensitivity and selectivity.

Platinum-Based Interdigitated Micro-Electrode Arrays for Reagent-Free Detection of Copper

Water is a precious resource that is under threat from a number of pressures, including, for example, release of toxic compounds, that can have damaging effect on ecology and human health. The current methods of water quality monitoring are based on sample collection and analysis at dedicated laboratories. Recently, electrochemical-based methods have attracted a lot of attention for environmental sensing owing to their versatility, sensitivity and their ease of integration with cost effective, smart and portable readout systems. In the present work, we report on the fabrication and characterization of platinum-based interdigitated microband electrodes arrays, and their application for trace detection of copper. Using square wave voltammetry after acidification with mineral acids, a limit of detection of 0.8 μg/L was achieved. Copper detection was also undertaken on river water samples and compared with standard analytical techniques. The possibility of controlling the pH at the surface of the sensors—thereby avoiding the necessity to add mineral acids—was investigated. By applying potentials to drive the water splitting reaction at one comb of the sensor’s electrode (the protonator), it was possible to lower the pH in the vicinity of the sensing electrode. Detection of standard copper solutions down to 5 μg/L (ppb) using this technique is reported. This reagent free method of detection opens the way for autonomous, in situ monitoring of pollutants in water bodies.