Cation Discrimination in Organic Electrochemical Transistors by Dual Frequency Sensing

In this work, we propose a strategy to sense quantitatively and specifically cations, out of a single organic electrochemical transistor (OECT) device exposed to an electrolyte. From the systematic study of six different chloride salts over 12 different concentrations, we demonstrate that the impedance of the OECT device is governed by either the channel dedoping at low frequency and the electrolyte gate capacitive coupling at high frequency. Specific cationic signatures, which originates from the different impact of the cations behavior on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer and their conductivity in water, allow their discrimination at the same molar concentrations. Dynamic analysis of the device impedance at different frequencies could allow the identification of specific ionic flows which could be of a great use in bioelectronics to further interpret complex mechanisms in biological media such as in the brain.Comment: Full text and supporting informatio

Sodium lactate solutions characterization using Electrochemical Impedance Spectroscopy

Lactate is an important metabolite in human body and, among possible medical applications, it can be used to monitor physical activity. Actually, its concentration represents a clear indication whether optimal training intensity is kept or if muscles are under anaerobic conditions. Routine procedures to measure lactate concentration during physical activity are represented by invasive measurements, which require blood sampling from the patient or the athlete. So, a great advantage would be derived by the possibility to monitor this analyte using non-invasive techniques. Considering the possibility to measure lactate in human sweat during sport activities, this paper presents the characterization of saline aqueous solutions containing sodium lactate by means of Electrochemical Impedance Spectroscopy (EIS). Measurements were performed using a two-electrode electrochemical cell and acquired spectra were analyzed also by means of equivalent electrical circuit (EEC) modeling. Results show an effect due to lactate concentration on solution impedance in the high-frequency region of spectrum, where a change in solution resistance is measured. At the same time, no changes in the measured capacitance were found. Future work will study the electrochemical behavior of lactate solutions also at higher frequencies to further investigate the possible use of EIS for lactate levels monitoring during sport activities

Electrical Properties of Model Lipid Membranes

Biological membranes are essential components of the living systems and processes occurring with their participation are related mainly to electric phenomena, such as signal transduction, the existence of membrane potentials, and transport through the membrane. It is well known that the universal model of the cell membrane structure is the lipid bilayer, which constitutes the environment for integral and surface membrane proteins. Thus, much attention has been given to the study of the organization and properties of these structures concerning both experimental and theoretical aspects. As systematic examinations are impeded by the complexity of the natural membranes, the best approach to conducting detailed physical and chemical studies of biological membranes is to use simplified well-defined model lipid membranes. Among the most commonly used are liposomes, planar lipid membranes, membranes on solid substrates, and lipid monolayers on the free surface.Studies of the electrical properties of model lipid membranes have been carried out for many years. However, there are still many issues that have not been verified experimentally and for which the existing results are incomplete or inconsistent. Therefore, the main objective of this book was to collect recent scientific and review articles on the electrical properties of model lipid membranes. This objective has been successfully achieved, for which I express heartfelt appreciation to all authors and reviewers for their excellent contributions

Electrochemical and surface plasmon bioassays for circulating biomarkers

To address analytical detection needs, sensitive and selective assay methodologies are of great importance. Compared to simple buffer medium, a great challenge exists in detecting ultra-low levels of biomarkers in clinical matrices due to their inherent complexity and interferences posed by non-specific molecules. In addition, small molecules do not yield measurable assay signal changes compared to large biomolecules. My thesis research is focused on designing nano-biological interfaces to detect small and large molecules at low parts-per-billion and femto/picomolar concentrations in complex biofluids (serum and urine samples). Compared to harsh and tedious chemical carboxylation, non-covalent carboxylation of multiwalled carbon nanotubes by π-π stacking 1-pyrenebutyric acid retains the innate sp2 structure and electronic properties of the nanotubes and offers surface carboxyl groups for stable covalent amine coupling of a large amount of enzymes, thus improving the sensitivity of the assay. Chapter 2 demonstrates the first pyrenyl carbon nanostructure modified enzymatic bioelectrode for amperometric detection of urine formaldehyde at clinically relevant parts-per-billion levels with selectivity and wide dynamic range. Subsequently, we explored the low dielectric permittivity and intrinsic plasmonics of graphene for the detection of serum glutamic acid decarboxylase autoantibody (GADA). Graphene-based electrochemical immunosensing approach is advantageous due to its additional applicability for surface plasmon based validation and binding strength analysis with surface immobilized GAD-65 antigens (Chapter 3). My thesis focused on the third class of biomarkers, microRNAs, which are small oligonucleotides with 21-25 bases. To develop the microRNA assay with quantitative characterization, surface plasmon resonance imaging (SPRi) coupled with quartz crystal microbalance (QCM) was designed (Chapter 4). Gold nanoparticles (Au NPs) were linked to the oligonucleotides to increase the detection sensitivity upon hybridization with the selective capture oligonucleotide immobilized on the sensor surface with minimal non-specific signals. Often, cancer and other similar health disorders have been shown to be related to various types of biomarkers. Hence, in Chapter 5, we designed a multiplex assay platform for combined measurement of proteins and microRNAs. For this multiplex assay, we synthesized iron-gold bimetallic core/shell nanoparticles (Fe3O4@Au NPs) that displayed a greater plasmonic signal amplification than either Fe3O4 or Au NPs.Chemistr

Covalent immobilization of delipidated human serum albumin on poly(pyrrole-2-carboxylic) acid film for the impedimetric detection of perfluorooctanoic acid

The immobilization of biomolecules at screen printed electrodes for biosensing applications is still an open challenge. To enrich the toolbox of bioelectrochemists, graphite screen printed electrodes (G-SPE) were modified with an electropolymerized film of pyrrole-2-carboxilic acid (Py-2-COOH), a pyrrole derivative rich in carboxylic acid functional groups. These functionalities are suitable for the covalent immobilization of biomolecular recognition layers. The electropolymerization was first optimized to obtain stable and conductive polymeric films, comparing two different electrolytes: sodium dodecyl sulphate (SDS) and sodium perchlorate. The G-SPE modified with Py-2-COOH in 0.1 M SDS solution showed the required properties and were further tested. A proof-of-concept study for the development of an impedimetric sensor for perfluorooctanoic acid (PFOA) was carried out using the delipidated human serum albumin (hSA) as bioreceptor. The data interpretation was supported by size exclusion chromatography and small-angle X-ray scattering (SEC-SAXS) analysis of the bioreceptor-target complex and the preliminary results suggest the possibility to further develop this biosensing strategy for toxicological and analytical studies

CHARACTERISATION OF PEDOT AND ITS DERIVATIVES IN ELECTROCHEMICAL SENSING APPLICATIONS

The emergence of a new class of polymer, namely conducting polymers (CPs) in late 1970s, has attracted many hysicists, chemists and materials researchers to study them in depth due to the unique properties and broad applications of this material. Poly(3,4-ethylenedioxythiophene) (PEDOT) has been found to be the most chemically stable CP to date. The aim of this project was to characterise PEDOT and its derivatives for applications in ion sensing. In this work, PEDOT and its derivatives i.e. poly(3,4-propylenedioxythiophene) (PProDOT) and poly(3,3-dibenzyl-3,4-propylenedioxythiophene) (PDBPD) doped with perchlorate ( ClO-4) have been electrochemically synthesised on glassy carbon (GC) and indium-tin-oxide coated glass (ITO) electrodes in acetonitrile. PEDOTs were also prepared in aqueous solutions using perchlorate ( ClO-4) and chloride( Cl-) counterions as comparison. Scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurements and Raman spectroscopy have been used to characterise the physical properties of the polymer coated glassy carbon (GC) and ITO electrodes. PDBPD has shown to have the most compact morphology, roughest and least wettable surface. The electrochemical studies have shown that PEDOT has the highest capacitive current. The combination of this property and mixed electronic and ionic conductivity make the PEDOT suitable to be used as a solid contact (transducer) in all-solid-state ion-selective electrode (ASSISE). PEDOT doped with poly(sodium 4-styrenesulfonate) (PSS) was found to be superior to hyaluronic acid (HA) as a solid contact for ASS Ca2+-, K+- and Na+-selective electrodes. Measurements of Ca2+ and K+ upon plant stress using ion ion-selective microelectrodes have been demonstrated. Chiral electrodes based on electrodeposited PEDOT doped with chiral molecules (collagen, HA and hydroxypropyl cellulose) were shown to discriminate between (R)-(−)- and (S)-(+)-mandelic acid. The work carried out in this thesis has shown that PEDOT is one of the most versatile conducting polymers

Selected Papers from the 1st International Electronic Conference on Biosensors (IECB 2020)

The scope of this Special Issue is to collect some of the contributions to the First International Electronic Conference on Biosensors, which was held to bring together well-known experts currently working in biosensor technologies from around the globe, and to provide an online forum for presenting and discussing new results. The world of biosensors is definitively a versatile and universally applicable one, as demonstrated by the wide range of topics which were addressed at the Conference, such as: bioengineered and biomimetic receptors; microfluidics for biosensing; biosensors for emergency situations; nanotechnologies and nanomaterials for biosensors; intra- and extracellular biosensing; and advanced applications in clinical, environmental, food safety, and cultural heritage fields

Study of overall and local electrochemical responses of oxide films grown on CoCr alloy under biological environments

The interaction of the physiological medium and living tissues with the implant surfaces in biological environments is regulated by biopotentials that induce changes in the chemical composition, structure and thickness of the oxide film. In this work, oxide films grown on CoCr alloys at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl have been characterized through overall and localized electrochemical techniques in a phosphate buffer solution and 0.3% hyaluronic acid. Nanopores of 10–50 nm diameter are homogeneously distributed along the surface in the oxide film formed at 0.7 V vs Ag/AgCl. The distribution of the Constant Phase Element studied by local electrochemical impedance spectroscopy showed a three-dimensional (3D) model on the oxide films grown at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl. This behaviour is especially noticeable in oxide films grown at 0.7 V vs Ag/AgCl, probably due to surface inhomogeneities, and resistive properties generated by the potentiostatic growth of the oxide film.This work was supported by the Spanish National government [MINECO-MAT2011-29152-C02-01].Peer reviewe

Electroanalytical investigations of bismuth electrodes and silver nanoparticles

PhD ThesisBismuth bulk electrodes (BiBEs) have been suggested as possible replacements for mercury electrodes in electroanalytical studies in part because they are simply prepared by melting bismuth powder in a glass capillary and also because of the relative lack of toxicity of Bi. The double layer of BiBEs in aqueous media was studied using electrochemical impedance spectroscopy (EIS). The differential capacitance of BiBEs was determined in three aqueous electrolytes: sodium nitrate (NaNO3), sodium bromide (NaBr) and sodium chloride (NaCl) as well as the nonaqueous electrolyte LiClO4/acetonitrile (AN). Comparative measurements were made with a polycrystalline platinum electrode. Up to 43 µF cm-2 were recorded for the double layer capacitance at the BiBEs in the aqueous electrolytes, while more typical capacitance values of <20 µF cm-2 were obtained for the Bi|AN/LiClO4 interface. Combined investigations by EIS and x-ray photoelectron spectroscopy (XPS) suggest the high values of capacitance in the aqueous electrolytes are due to pseudocapacitance effects, owing to adsorptions of bromide and chloride ions as well as the formation/reduction of a bismuth(III) oxide film at the electrode surface. The capacitance values of the Bi|AN/LiCO4 interface are consistent with the standard Gouy-Chapman-Stern model; ClO4- anions are thought to be weakly adsorbing in non-aqueous media. The EIS measurements also enabled the determination of the potential of zero charge PZC of -0.49 V versus Ag/AgCl at BiBEs in the aqueous electrolyte mixture of NaNO3/NaCl. The differential capacitance studies provided an understanding of the nature of the BiBE interfaces required to interpret electron transfer measurements. Several redox couples were investigated by slow scan cyclic voltammetry (CV): ruthenium hexaammine, methyl viologen, sodium anthraquinone-2-sulfonate monohydrate, methylene blue, toluidine blue, hexaamminecobalt(III) chloride and cobaltocenium hexafluorophosphate. Many of these couples showed complex behaviour at Bi; either due to Bi oxidation or a lack of chemical reversibility and possible complications due to adsorption. However, ruthenium hexaamine showed reversible, uncomplicated CVs at the BiBE/KCl(aq) interface and therefore was selected for detailed study of the electron transfer kinetics by EIS.The standard rate constant (ko) and electron transfer coefficient (α) were determined for the outer-sphere one-electron transfer process for ruthenium hexaammine trichloride Ru(NH3)6Cl3 at BiBEs in KCl(aq) as supporting electrolyte. In contrast to previous work on viologen derivatives in AN in the literature, there was a marked difference between the ko values at BiBEs and Pt electrodes- the voltammetry and impedance spectra were found to be reversible at Pt. We ascribe this difference to the presence of a thin oxide layer on the BiBE at potentials near the standard potential for ruthenium hexaammine. Despite the presence of such an oxide layer, repeatable impedance spectra could be obtained for the system and the expected linear dependence of the charge transfer resistance on [Ru(III)] was observed. Further, the (dc) potential dependence of the EIS data allowed the determination of the potential dependence of the transfer coefficient. This data provided direct evidence of the importance of double layer corrections to ko because of the rapid variation of α observed near the potential of zero charge. In summary, BiBEs show somewhat complex behaviour in aqueous media; many redox couples cannot be easily studied because of the susceptibility of Bi to oxidation and complex adsorption effects, not well understood. However in the case of ruthenium hexaammine, precise voltammetric data can be obtained even though photoemission spectra and differential capacitance data indicates the presence of a thin oxide film. ii The second part of the thesis concerns the detection of Ag(I) ions released by corrosion of silver nanoparticles (AgNPs) in aqueous media. Neither BiBEs nor Pt electrodes were found to be suitable for the detection of Ag(I), however straightforward anodic stripping voltammetry (ASV) at glassy carbon electrodes was successful. AgNPs were synthesized by the citrate reduction method and dialysed either in pure water, or different concentrations of chloride and sulphate to examine the effect of the medium on the release of Ag(I) ions. The importance of these studies relate to the fate of AgNPs in the environment; AgNPs are now widely employed for their antimicrobial activity, however it is not clear what their eventual fate is nor how much Ag(I), the putative agent is released. The experimental technique involved dialysis of the initial AgNP preparation against a particular aqueous medium and (i) analysis of the [Ag(I)] released from the dialysis membrane into the external medium and (ii) characterization of the aliquots of AgNPs remaining inside the dialysis membrane. Optical absorption spectra showed a redshift of the AgNP plasmon band throughout the dialysis, consistent with aggregation of the NPs. This is unexpected based on simple DLVO stabilization as the reduction in ionic strength against water should disfavour aggregation. However it was confirmed by dynamic light scattering (DLS) and atomic force microscopy (AFM) of drop-cast aliquots and probably arises from loss of citrate ligands. Release of Ag(I) ions was monitored by anodic stripping voltammetry at glassy carbon electrodes. The ASV data was calibrated by standard addition and indicated the presence of about 90 µM of Ag(I) ions in the initial preparation. Over time, the [Ag(I)] decreased until it reached a steady-state value of the order of a few µM. Unexpectedly, a similar steady-state concentration was observed in chloride or sulphate containing media. The presence of chloride does indeed reduce the concentration of Ag(I) in the initial preparation (to a value controlled by the solubility product of AgCl), however in that case a strong decrease in [Ag(I)] throughout the dialysis was not observed. A concentration of about 4 µM was still detected after 73 h of dialysis. This effect is interpreted in terms of the decrease in the electrode potential for the Ag/Ag(I) couple in the presence of Cl-; we suggest that the steadystate concentration of Ag(I) is determined mainly by the corrosion of the AgNPs.Benue State University Makurdi and the Nigerian Tertiary Education Trust Fun