The Composite Material of (PEDOT-Polystyrene Sulfonate)/Chitosan-AuNPS-Glutaraldehyde/as the Base to a Sensor with Laccase for the Determination of Polyphenols.

The described research aimed to develop the properties of the conductive composite /poly(3,4-ethylenedioxy-thiophene-poly(4-lithium styrenesulfonic acid)/chitosan-AuNPs-glutaraldehyde/ (/PEDOT-PSSLi/chit-AuNPs-GA/) and to develop an electrochemical enzyme sensor based on this composite material and glassy carbon electrodes (GCEs). The composite was created via electrochemical production of an /EDOT-PSSLi/ layer on a glassy carbon electrode (GCE). This layer was covered with a glutaraldehyde cross-linked chitosan and doped with AuNPs. The influence of AuNPs on the increase in the electrical conductivity of the chitosan layers and on facilitating the oxidation of polyphenols in these layers was demonstrated. The enzymatic sensor was obtained via immobilization of the laccase on the surface of the composite, with glutaraldehyde as the linker. The investigation of the surface morphology of the GCE/PEDOT-PSSLi/chit-AuNPs-GA/Laccase sensor was carried out using SEM and AFM microscopy. Using EDS and Raman spectroscopy, AuNPs were detected in the chitosan layer and in the laccase on the surface of the sensor. Polyphenols were determined using differential pulse voltammetry. The biosensor exhibited catalytic activity toward the oxidation of polyphenols. It has been shown that laccase is regenerated through direct electron transfer between the sensor and the enzyme. The results of the DPV tests showed that the developed sensor can be used for the determination of polyphenols. The peak current was linearly proportional to the concentrations of catechol in the range of 2-90 µM, with a limit of detection (LOD) of 1.7 µM; to those of caffeic acid in the range of 2-90 µM, LOD = 1.9 µM; and to those of gallic acid in the range 2-18 µM, LOD = 1.7 µM. Finally, the research conducted in order to determine gallic acid in a natural sample, for which white wine was used, was described.

Electrochemical study of ephedrine at the polarized liquid-liquid interface supported with a 3D printed cell.

In this work, we have examined an electrochemical behavior of the ephedrine at the polarized liquid-liquid interface (water/1,2-dichloroethane). In this respect, we first designed and then 3D printed polyamide-based electrochemical cell that was used as the liquid-liquid interface support during electroanalytical measurements. The protonated ephedrine undergoes a reversible ion transfer reaction with the standard Galvani potential difference equal to +0.269 V. This value was used to calculate the water - 1,2-dichloroethane logP equal to -4.6. Ion transfer voltammetry was used to build the calibration curve and allowed for the ephedrine detection from concentration equal to 20 µM. By varying the pH of the aqueous phase from 2 up to 12 we were able to plot the ion partition diagram that was further analyzed and provided several pharmacochemical information. To further push this work towards practical utility, we have formulated the artificial urine and studied the interfacial behavior of all its components at the polarized liquid-liquid interface. Ephedrine detection from real spiked urine samples was also performed.

The role of tannic acid and sodium citrate in the synthesis of silver nanoparticles.

We describe herein the significance of a sodium citrate and tannic acid mixture in the synthesis of spherical silver nanoparticles (AgNPs). Monodisperse AgNPs were synthesized via reduction of silver nitrate using a mixture of two chemical agents: sodium citrate and tannic acid. The shape, size and size distribution of silver particles were determined by UV-Vis spectroscopy, dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM). Special attention is given to understanding and experimentally confirming the exact role of the reagents (sodium citrate and tannic acid present in the reaction mixture) in AgNP synthesis. The oxidation and reduction potentials of silver, tannic acid and sodium citrate in their mixtures were determined using cyclic voltammetry. Possible structures of tannic acid and its adducts with citric acid were investigated in aqueous solution by performing computer simulations in conjunction with the semi-empirical PM7 method. The lowest energy structures found from the preliminary conformational search are shown, and the strength of the interaction between the two molecules was calculated. The compounds present on the surface of the AgNPs were identified using FT-IR spectroscopy, and the results are compared with the IR spectrum of tannic acid theoretically calculated using PM6 and PM7 methods. The obtained results clearly indicate that the combined use of sodium citrate and tannic acid produces monodisperse spherical AgNPs, as it allows control of the nucleation, growth and stabilization of the synthesis process. Graphical abstractᅟ.

Electrodes Modified with Composite Layers Based on Poly(3,4-ethylenedioxythiophene) as Sensors for Paracetamol.

Two sensors for paracetamol were obtained on the basis of a GC electrode modified with poly(3,4-ethylenedioxythiophene) (PEDOT). The first sensor was a GC electrode modified with a conductive composite layer of PEDOT doped with poly(4-lithium styrenesulfonic acid) (PSSLi), and the second one was a GC electrode modified by a composite of PEDOT doped with PSSLi and multiwall carbon nanotubes (MWCNT). A conductive PEDOT polymer film was used as an electron mediator with a rich electron cloud. Both sensors were developed for the determination of paracetamol (ACOP) in the presence of interference compounds. Differential pulse voltammetry (DPV) and adsorptive stripping differential pulse voltammetry (AdsDPV) were applied as analytical methods. The modified electrodes were successfully employed for the determination of ACOP in a pharmaceutical formulation.

Immobilization of glucose oxidase on modified electrodes with composite layers based on poly(3,4-ethylenedioxythiophene).

Two modified electrodes with immobilized glucose oxidase were developed. Modification with poly(3,4-ethylenedioxythiophene) (PEDOT) and polyacrylic acid (PAA) doped with poly(4-lithium styrenesulfonic acid) (PSSLi) in a newly elaborated procedure was used in the first electrode. The second one presents innovative solution and consists of two sublayers; one of them was PEDOT doped with PSSLi and the other was composed of PEDOT and anthranilic acid (AA) doped with poly(4-styrenesulfonic acid) (PSSH). Glucose oxidase was covalently bonded with the carboxyl groups of the polymer through N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (WSC). The activity of immobilized enzyme was confirmed by spectrophotometry using the reaction of the produced hydrogen peroxide with o-dianisidine. The procedure for immobilization was optimized. It was found that the choice of an appropriate doping agent and its concentration were significant and 0.1M PSSLi proved to be the best doping agent. The most efficient immobilization was established for WSC and GOD concentration at the level of 4mg/ml and 5mg/ml respectively. In both cases, it was found that a small deviation from the concentrations determined to cause a sharp decrease in the activity of the enzyme, which was proven by spectrophotometric measurements. Prepared electrodes were active over a month with repeatable measurement results.