Investigations of electrochemical polymerization processes of thin poly(pyrrole) films and its application to anion sensor based on surface plasmon resonance

Towards electrochemical surface plasmon resonance sensor based on the molecularly imprinted polypyrrole for glyphosate sensing

In this research the molecular imprinting technology was applied for the formation of glyphosate-sensitive layer. The glyphosate imprinted conducting polymer polypyrrole (MIPpy) was deposited on a gold chip/electrode and used as an electrochemical surface plasmon resonance (ESPR) sensor. The results described in this study disclose some restrictions and challenges, which arise during the development of glyphosate ESPR sensor based on the molecularly imprinted polymer development stage. It was demonstrated, that glyphosate could significantly affect the electrochemical deposition process of molecularly imprinted polymer on the electrode. The results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR) have demonstrated that glyphosate molecules tend to interact with bare gold electrode and thus hinder the polypyrrole deposition. As a possible solution, the formation of a self-assembled monolayer (SAM) of 11-(1H-Pyrrol-1-yl)undecane-1-thiol (PUT) before electrochemical deposition of MIPpy and NIPpy was applied. Dissociation constant (KD) and free energy of Gibbs (ΔG0) values of glyphosate on MIPpy and Ppy without glyphosate imprints (NIPpy) were calculated. For the interaction of glyphosate with MIPpy the KD was determined as 38.18 ± 2.33⋅10-5 and ΔG0 as -19.51 ± 0.15 kJ/mol.

Electrochemical polypyrrole formation from pyrrole 'adlayer'

In this research study, we investigated the morphology of polypyrrole nanostructures, which were formed during the electrochemical deposition of conducting polymer. An electrochemical quartz crystal microbalance (EQCM) cell equipped with a flow-through system was employed to exchange solutions of different compositions within the EQCM cell. When bare PBS buffer in the EQCM cell was exchanged with PBS buffer with pyrrole we observed a distinct increase in the resonance frequency Δf. This change in the resonance frequency and electrical capacitance, which was calculated from electrochemical impedance spectroscopy (EIS) data, illustrate that pyrrole on the surface of the gold electrode formed an adsorbed layer (adlayer). The formation of a pyrrole adlayer before the potential pulse that induced polymerization was investigated by QCM-based measurements. The electrochemical polymerization of this adlayer was induced by a single potential pulse and a nanostructured layer, which consisted of adsorbed polypyrrole (Ppy) nanoparticles with a diameter of 50 nm, was formed. QCM and EIS data revealed that by the next cycle of the electrochemical formation of Ppy, which was investigated after flow-through-based exchange of solutions, the initially formed Ppy surface was covered by the adlayer of pyrrole. This adlayer was desorbed when pyrrole was removed from the solution. When electrochemical polymerization was performed using 50 potential pulses, a Ppy layer, which had more complex morphology, was formed on the EQCM crystal. Scanning electron microscopy showed that the conductivity of this layer was unequally distributed. We observed that the polypyrrole layer formed by electrochemical deposition, which was performed using potential pulses, was formed out of aggregated spherical Ppy particles with a diameter of 50 nm.

Quartz crystal microbalance-based evaluation of the electrochemical formation of an aggregated polypyrrole particle-based layer

Electrochemical quartz crystal microbalance (EQCM) was used for the evaluation of conducting polymer polypyrrole (Ppy), which was formed by a sequence of potential pulses on a Au-plated EQCM disc. The Ppy layer was obtained from freshly prepared polymerization solution consisting of pyrrole that was dissolved in phosphate buffer. The main aim of the study was to determine some aspects of the Ppy layer formation process. The polymerization process was estimated by EQCM and chronoamperometry. The Cottrell equation was used for the integration of total charge that was passing through the electrochemical cell during the formation of the Ppy-based layer. It was found that the charge of the electrical double layer, which was estimated while applying an Anson plot, is negative. From this observation, it could be assumed that the pyrrole oxidation process could be well described by principles of heterogeneous kinetics. The negative value of the electrical double layer was the result of a charge-transfer restriction. This restriction of charge transfer could occur due to partial blocking of the electrode surface by an aggregated Ppy particle-based layer. Quartz crystal motional resistance (R) was taken into account during this research. Ppy layer formation is represented schematically on the basis of the obtained experimental results and analytical data.