Porous calcium copper titanate electrodes for paracetamol degradation by electro-oxidation via CuO-induced peroxymonosulfate activation

Some drugs cannot be efficiently eliminated using routine wastewater treatments and therefore are considered persistent organic pollutants (POPs). POPs can be removed using advanced oxidation processes. Among these processes, the combination of electrocatalysis and a sulfate-based advanced oxidation process via peroxymonosulfate (PMS) activation is an attractive approach due to its high efficiency, low energy consumption and non-selective attack. It is well known that the type of anode strongly affects the electrocatalysis performance for water treatment. Here, we evaluated perovskites as electrode material due to their unique structural properties and high chemical stability. We fabricated porous anodes of calcium copper titanate (CaCu3Ti4O12; CCTO) with different percentages (20%, 30% and 40%) of polymethyl methacrylate (PMMA) by ball-milling. The samples that included PMMA displayed 50% porosity and pores were homogenously distributed. Morphological measurements show the presence of grain structures and grain boundaries containing CCTO and CuO phases, respectively. CCTO with 30 wt% PMMA (CCTO-30) exhibited the highest CuO phase amount, defect percentage and oxidation–reduction peak, and the smallest resistance. We used the obtained CCTO nanocomposites as anodes in a beaker (210 mL) with PMS (0.5 mM) to treat 10 ppm paracetamol in 50 mM sodium sulfate. After 90 minutes, paracetamol was completely decomposed using CCTO-30 due to PMS activation by a copper catalytic cycle (Cu2+/Cu1+ and Cu2+/Cu3+) to generate ˙SO4− radicals and Cu3+ non-radicals that are selective for its removal

Affinity Sensors for the Diagnosis of COVID-19

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was proclaimed a global pandemic in March 2020. Reducing the dissemination rate, in particular by tracking the infected people and their contacts, is the main instrument against infection spreading. Therefore, the creation and implementation of fast, reliable and responsive methods suitable for the diagnosis of COVID-19 are required. These needs can be fulfilled using affinity sensors, which differ in applied detection methods and markers that are generating analytical signals. Recently, nucleic acid hybridization, antigen-antibody interaction, and change of reactive oxygen species (ROS) level are mostly used for the generation of analytical signals, which can be accurately measured by electrochemical, optical, surface plasmon resonance, field-effect transistors, and some other methods and transducers. Electrochemical biosensors are the most consistent with the general trend towards, acceleration, and simplification of the bioanalytical process. These biosensors mostly are based on the determination of antigen-antibody interaction and are robust, sensitive, accurate, and sometimes enable label-free detection of an analyte. Along with the specification of biosensors, we also provide a brief overview of generally used testing techniques, and the description of the structure, life cycle and immune host response to SARS-CoV-2, and some deeper details of analytical signal detection principles

Effects of Electric Potential Treatment of a Chromium Hexacyanoferrate Modified Biosensor Based on PQQ-Dependent Glucose Dehydrogenase

A novel potential treatment technique applied to a glucose biosensor that is based on pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH) and chromium hexacyanoferrate (CrHCF) incorporated into a platinum (Pt) electrode was demonstrated. CrHCF, serving as a mediator, was electrochemically deposited on the Pt electrode as ascertained by CV, SEM, FTIR and XPS measurements. The potential treatment of CrHCF, which converts Fe(II) to Fe(III), enables the glucose detection. The amperometric measurement linearity of the biosensor was up to 20 mM (R = 0.9923), and the detection sensitivity was 199.94 nA/mM per cm2. More importantly, this biosensor remained stable for >270 days

Doped Overoxidized Polypyrrole Microelectrodes as Sensors for the Detection of Dopamine Released from Cell Populations

A surface modification of interdigitated gold microelectrodes (IDEs) with a doped polypyrrole (PPy) film for detection of dopamine released from populations of differentiated PC12 cells is presented. A thin PPy layer was potentiostatically electropolymerized from an aqueous pyrrole solution onto electrode surfaces. The conducting polymer film was doped during electropolymerization by introducing counter-ions in the monomer solution. Several counter-ions were tested and the resulting electrode modifications were characterized electrochemically to find the optimal dopant that increases sensitivity in dopamine detection. Overoxidation of the PPy films was shown to contribute to a significant enhancement in sensitivity to dopamine. The changes caused by overoxidation in the electrochemical behavior and electrode morphology were investigated using cyclic voltammetry and SEM as well as AFM, respectively. The optimal dopant for dopamine detection was found to be polystyrene sulfonate anion (PSS-). Rat pheochromocytoma (PC12) cells, a suitable model to study exocytotic dopamine release, were differentiated on IDEs functionalized with an overoxidized PSS--doped PPy film. The modified electrodes were used to amperometrically detect dopamine released by populations of cells upon triggering cellular exocytosis with an elevated K+ concentration. A comparison between the generated current on bare gold electrodes and gold electrodes modified with overoxidized doped PPy illustrates the clear advantage of the modification, yielding 2.6-fold signal amplification. The results also illustrate how to use cell population based dopamine exocytosis measurements to obtain biologically significant information that can be relevant in, for instance, the study of neural stem cell differentiation into dopaminergic neurons

Development of an Alcohol Dehydrogenase Biosensor for Ethanol Determination with Toluidine Blue O Covalently Attached to a Cellulose Acetate Modified Electrode

In this work, a novel voltammetric ethanol biosensor was constructed using alcohol dehydrogenase (ADH). Firstly, alcohol dehydrogenase was immobilized on the surface of a glassy carbon electrode modified by cellulose acetate (CA) bonded to toluidine blue O (TBO). Secondly, the surface was covered by a glutaraldehyde/bovine serum albumin (BSA) cross-linking procedure to provide a new voltammetric sensor for the ethanol determination. In order to fabricate the biosensor, a new electrode matrix containing insoluble Toluidine Blue O (TBO) was obtained from the process, and enzyme/coenzyme was combined on the biosensor surface. The influence of various experimental conditions was examined for the characterization of the optimum analytical performance. The developed biosensor exhibited sensitive and selective determination of ethanol and showed a linear response between 1 × 10−5 M and 4 × 10−4 M ethanol. A detection limit calculated as three times the signal-to-noise ratio was 5.0 × 10−6 M. At the end of the 20th day, the biosensor still retained 50% of its initial activity

Investigations on the Mechanical Properties of Conducting Polymer Coating-Substrate Structures and Their Influencing Factors

This review covers recent advances and work on the microstructure features, mechanical properties and cracking processes of conducting polymer film/coating- substrate structures under different testing conditions. An attempt is made to characterize and quantify the relationships between mechanical properties and microstructure features. In addition, the film cracking mechanism on the micro scale and some influencing factors that play a significant role in the service of the film-substrate structure are presented. These investigations cover the conducting polymer film/coating nucleation process, microstructure-fracture characterization, translation of brittle-ductile fractures, and cracking processes near the largest inherent macromolecule defects under thermal-mechanical loadings, and were carried out using in situ scanning electron microscopy (SEM) observations, as a novel method for evaluation of interface strength and critical failure stress

Sarcosine oxidase composite screen-printed electrode for sarcosine determination in biological samples

As the prostate cancer (PCa) progresses, sarcosine levels increase both in tumor cells and urine samples, suggesting that this metabolite measurements can help in the creation of non-invasive diagnostic methods for this disease. In this work, a biosensor device was developed for the quantification of sarcosine via electrochemical detection of H2O2 (at 0.6 V) generated from the catalyzed oxidation of sarcosine. The detection was carried out after the modification of carbon screen printed electrodes (SPEs) by immobilization of sarcosine oxidase (SOX) on the electrode surface. The strategies used herein included the activation of the carbon films by an electrochemical step and the formation of an NHS/EDAC layer to bond the enzyme to the electrode, the use of metallic or semiconductor nanoparticles layer previously or during the enzyme immobilization. In order to improve the sensor stability and selectivity a polymeric layer with extra enzyme content was further added. The proposed methodology for the detection of sarcosine allowed obtaining a limit of detection (LOD) of 16 nM, using a linear concentration range between 10 and 100 nM. The biosensor was successfully applied to the analysis of sarcosine in urine samples

Electropolymerised molecularly imprinted polymers for the heat-transfer based detection of microorganisms: A proof-of-concept study using yeast

In this contribution, molecularly imprinted polymers (MIPs) were electropolymerised onto screen-printed carbon electrodes (SPCEs) to develop specific sensors for thermal detection of yeast. A laboratory yeast strain free of interferents was used to optimise the polymerisation procedure, whereas yeast in a complex mixture (yeast for baking) was employed to produce the final sensors and demonstrate proof-of-application. Two different electropolymerisation methods were employed, cyclic voltammetry and chronoamperometry respectively; the electrochemical methodology allows for controlled deposition and the ability to tailor the polymer surface to the required application. Infrared spectroscopy and scanning electron microscopy confirmed that the methods led to different structures; with cyclic voltammetry a high surface area was achieved, whereas for chronoamperometry a dense film was formed. Subsequently, these functionalised electrodes were inserted into a home-made thermal device that can measure the selective binding of yeast cells to the MIP layer via monitoring the thermal resistance (R ) at the solid–liquid interface. The results of the measurements showed that MIP-functionalised electrodes produced, according to both methods, a significant response in thermal signal for the MIP-functionalised electrode, which was not the case for the reference Non-Imprinted Polymer (NIP)-functionalised electrode. This demonstrated that thermal analysis can be employed for the detection of yeast, even in a complex sample such as food. To our knowledge, this is the first report of MIPs electropolymerised onto screen-printed electrodes for the thermal detection of fungi. The proposed approach enables the fast production of low-cost electrodes using a simple manufacturing procedure compatible with a portable device, implying high commercial potential. In the future, this could be adapted to a broad range of microorganisms including bacteria. t

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered