1,720,981 research outputs found
How low does the oxygen concentration go within a sandwich-type amperometric biosensor? Part 2: Theory for PPO biosensors
No full textA mathematical model to describe the amperometric response of a sandwich-type biosensor containing polyphenol oxidase as the recognition catalytic element is proposed. The model was solved numerically and the resulting nonlinear solution was used to simulate chronoamperometric curves as well as to estimate the concentration profiles of reagents and products of the enzymatic reaction within the sensor. Fromm's systematic method was applied to get a kinetic expression for the analysis of polyphenol oxidase enzymes. The simulated data are compared with curves corresponding to a biosensor prepared with an oxidase enzyme that reacts according to a ping-pong mechanism. Although in both cases oxygen is used as mediator of the enzymatic reaction, the electrochemical step can generate it back from the H2O2 released by enzymes such as glucose oxidase but it cannot do the same in the case of working with polyphenol oxidase. Most of the calculated profiles and related data are presented using dimensioned variables so that they can be directly compared with experimental results. Relevant parameters such as limit current, response-time, and sensitivity are analyzed as function of the thickness of membranes, concentration of enzyme and concentration of substrate.Fil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
Adsorptive square-wave voltammetry of quasi-reversible electrode processes with a coupled catalytic chemical reaction
Get PDFThere are several strategies for enhancing the sensitivity of electroanalytical methods. Usually, those strategies are based on the selection of the voltammetric technique, the inclusion of an accumulation step, and the eventual addition of a catalytic chemical reaction that regenerates the electroactive species. Square-wave voltammetry (SWV) is one of the most sensitive techniques. In the case of electroanalytical applications, it is typically preceded by an electrochemical or adsorptive pre-concentration step. In this manuscript, the theory of SWV for a quasi-reversible electrode process coupled to a catalytic chemical reaction between an adsorbed reagent and a soluble product is presented. The dependences of the dimensionless net peak current and its peak potential on the value of the standard charge transfer rate constant are described. The variation of the SWV parameters such as frequency and potential pulse amplitude are discussed. The effect of the chemical and electrochemical kinetics on the voltammetric profile is analyzed.Fil: Vettorelo, Sabrina Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
A robust and practically free of charge intermittent use glucose biosensor
Get PDFIn the past decades, great effort has been put in finding new electrode surface modifiers and enzyme immobilizer agents that prevent the enzyme leakage, minimize the effect of interfering species, retain the enzyme bioactivity, and enhance the sensor sensitivity. In this work, a sandwich-type glucose biosensor that keeps its sensitivity and operational linear range for more than a year is presented. After 5 months of intermittent use, where the biosensor was exposed to more than 500 standard additions, it presented a limit of detection of 5 μM, and the linear behavior was from 5 μM to 3 mM with a value of r2 = 0.999. Besides, after 7 months of its assembling, the biosensor was employed for assessing the glucose concentration of real serum samples and its performance was compared with the response of a commercial autoanalyzer. A year later, the biosensor still exhibited very good performance of its analytical parameters. The performance of identical sandwich-type biosensors is analyzed when they are exposed to three different storage conditions. Simulated curves are compared with experimental data to explain the dependence of sensitivity and response-time on the aging and storage conditions of the biosensors.Fil: Colombo, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
Theory of square-wave catalytic adsorptive stripping voltammetry. How to obtain mechanistic information from experimental data
Get PDFThe sensitivity of a catalytic adsorptive stripping voltammetric method depends mainly on the strength of adsorption of the electroactive reactant and the efficiency of the catalytic reaction. While the strength of adsorption is associated with the type of reagent and the solution pH, the efficiency of the catalytic step depends on the type and concentration of the oxidant selected for such reaction. Although the probe-and-error approach is commonly used for optimizing a given analytical signal, information about the reaction scheme and some good estimation about the rate constants of involved reactions would help a lot to optimize the analytical system.The possibility for using the quasi-reversible maximum to study the electrode kinetics depends on the values of kcat, Kad, f, Esw, and of course ks. As a result of this, it is rather difficult for experimentalist and also for theoreticians to organize a strategy for detecting and understanding the effect of each variable separately. In this manuscript, it is first shown the effect of different variables on the voltammetric response, and then it is suggested a strategy for studying and estimating the values of those variables. Thus, if the experimental system matches the reaction scheme of an electrochemical reaction complicated by following homogeneous catalytic reaction, then it is advisable to follow a set of simple experimental steps to characterize the kinetic constants of the system.Fil: Vettorelo, Sabrina Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
A novel planar electrochemical cell for voltammetric measurements in thin hydrogel films
Get PDFThe fabrication of a planar micro electrochemical cell is presented.The simplicity and the relative low cost of this kind of cells make them very interesting and promising in the development of chemical and biochemical sensors. The utilization of microelectrodes as working electrodes in planar electrochemical cells is preferred to the conventional macroelectrodes because microelectrodes can be used in highly resistive media, have short response time, and excellent signal to noise ratio. In electrochemical sensor applications, the microelectrode surfaces are commonly modified with multiple layers to boost selectivity, control sensitivity, or to provide a biocompatible interface between the sensor and its environment. In this work, the fabricated set of bundled electrodes is covered with a hydrogel as an example of its potential use as electrochemical gas sensor. All micro electrochemical cells were characterized by cyclic voltammetry (CV) and the results were analyzed with different statistical methods.Fil: Kékedy Nagy, Laszlo. University of Memphis; Estados UnidosFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Lindner, Ernö. University of Memphis; Estados Unido
Analysis and optimization of a hydrogel matrix for the development of a sandwich-type glucose biosensor
No full textThe development of a sandwich-type biosensor for glucose quantification is presented. This work is focused on the optimization of the enzymatic matrix of the biosensor. The best performance was found for an enzymatic matrix composed by 30% w/w mucin, 70% w/w albumin, 1.35 U glucose oxidase (GOX) per sensor, and glutaraldehyde diluted to 3%. The crosslinking with glutaraldehyde transforms this mixture into a hydrogel that is entrapped between two membranes of polycarbonate. The selected sandwich-type biosensor showed very good response time, sensitivity, stability, and sensor-to-sensor reproducibility. According to the results presented in this manuscript, a biosensor prepared with very high amount of enzyme would not necessarily increase the analytical signal. Simulated curves are compared with experimental data to explain the dependence of sensitivity on the concentration of enzyme. In addition, this kind of comparison represents a quite simple way to estimate the value of vmax≈0.13 M s-1 from the amperometric response of a sensor prepared with 1.34 U of GOX. Considering that sandwich-type biosensors are commonly assembled as part of devices where the sample is diluted with buffer, the more than 3 orders of magnitude of linear behavior of this sensor would ensure the possibility for assessing any sample.Fil: Colombo, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Baruzzi, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
How to obtain kinetic information in thin-film voltammetry from the comparison of SCV and SWV responses
No full textThin-film voltammetry (TFV) has one of the simplest experimental setups for studying the electrochemical processes that take place at liquid/liquid interfaces. This is because in TFV it is possible to neglect the iR drop of the non-aqueous solvent, when it corresponds to an organic thin film attached to the working electrode. In this manuscript the theory of TFV is used for describing how the electrochemical responses of staircase cyclic voltammetry (SCV) and square-wave voltammetry (SWV) are affected by the confinement of electroactive species in a thin film that is in contact with the working electrode. The reason for comparing the responses of these two techniques is established on the different concentration profiles that the electroactive species present within the thin-film and the implications that it has on the voltammetric responses of each technique. According to our analysis, the presence of the so-called “quasi-reversible maximum” cannot be used in TFV for estimating kinetic parameters since it would lead to erroneous results. This is because both the apparent kinetic and the apparent thickness change simultaneously with the variation of the scan-rate of each technique. Instead of this, it is proposed a strategy based on the variation of the scan-rate of SCV and SWV. Thus, it is possible to obtain 2 sets of voltammograms whose peak currents and peak potentials characterize the kinetic and thickness of the system. The estimation can be made when all the peak parameters fit properly to the theoretical data provided in this manuscript. Besides, it is shown that the results of SCV and SWV complement each other providing the way for estimating the formal charge transfer rate constant and the thickness of this kind of systems.Fil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Vettorelo, Sabrina Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
Optimization of a reusable sandwich-type amperometric phenol biosensor. Experimental and theoretical outcomes
No full textThe development of reproducible and stable enzyme-based amperometric biosensors for the analysis of phenolic compounds present in food and plants is still a challenge in electroanalytical chemistry. This study describes the optimization process of a sandwich-type amperometric biosensor for detecting oxidizable phenolic compounds. Enzymatic matrix optimization was carried out via a combinatorial study focusing on sensitivity, linear range, and response time. Repeatability and reproducibility studies show variations of only 3 % and 4 %, respectively. When exposed to catechol solutions, the biosensor has a detection limit of 0.9 µM and its linear behavior involves practically three orders of magnitude. This wide linear range can be explained considering that the consumption of oxygen in the nearest of the biosensor limits the enzymatic reaction. The analyses by Michaelis’ equation might give erroneous results, depending on the concentration of phenolic compounds. The exposition of the proposed biosensor to high concentrations of oxidizable phenols produces large amounts of polyphenols that limit its stability. Accordingly, although the biosensors prepared with a high amount of enzyme will have the highest sensitivity values, the proliferation of polyphenols and oxygen consumption may limit their linear range and stability more rapidly. Thus, the long-term stability of a phenol biosensor should be informed not only considering the number of days after its assembling but also the number of times of use and the concentration of phenols to which it was exposed.Fil: Zoratti, Marianela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; ArgentinaFil: Colombo, Lucas. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Fisicoquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
How low does the oxygen concentration go within a sandwich-type amperometric biosensor?
No full textSoftware for the automatic non-linear least squares fit of chronoamperometric responses corresponding to sandwich-type amperometric biosensors has been developed. The so-called Simplex algorithm computes a minimum value for the difference between experimental and theoretical data. The latter consider a numerical model based on a ping-pong reaction mechanism corresponding to an oxidase enzyme that has been immobilized between diffusion membranes. The results obtained from the simulation of a first-generation lactate biosensor in presence of 0.1 mM substrate indicate that the concentration of O 2 would decrease only 0.1% with regards to its bulk value. Besides, the concentration of this natural mediator would remain practically unchanged during a typical calibration curve. This is because the rather high diffusion coefficient of O 2 and its regeneration at the electrode surface minimize the concentration changes of this species. In addition, it was found that the thicknesses of polycarbonate membranes and the enzymatic matrix have average values of 13 μm and 20 μm, respectively. However, these membranes might exhibit smaller thickness depending on the time provided for the crosslinking reaction. In this regard, if this reaction is slow enough, the enzymatic matrix would be able to diffuse through the pores of polycarbonate membranes and they will appear to be thinner than expected. This effect may compromise the response-time and the reproducibility of this kind of biosensors.Fil: Romero, Marcelo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Baruzzi, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
Mathematical modeling and experimental results of a sandwich-type amperometric biosensor
No full textA comprehensive numerical treatment of the diffusion and reaction within a sandwich-type amperometric biosensor is presented. The model considers that the enzyme reacts according to a ping-pong mechanism and that it is entrapped into a so-called enzymatic matrix placed between two diffusion membranes. It is found that the concentrations of reagents and products within the sensor are difficult of being compared to those of the bulk. In this regard, the use of approximate analytical solutions would involve errors in the analysis of kinetic parameters corresponding to this kind of biosensors. Provided the mediator species are in high concentration or diffuse much faster than the substrate, the response time of a biosensor of this kind would be determined by the diffusion of the substrate though the external membrane. In this sense, those systems with immobilized mediators, in which diffusion of electrons or holes is assumed for the charge transport process, could be also described by this model. Thus, the thickness and the permeability to the analyte of the external membrane are critical parameters for improving the response time of a sandwich-type biosensor. The simulated curves are compared with experimental profiles corresponding to a lactate amperometric biosensor obtaining consistent results. In a future publication a non-linear fitting algorithm will be combined to the model for the extraction of kinetic and/or geometric parameters.Fil: Romero, Marcelo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Baruzzi, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin
- …
