In situ studies of protein adsorptions on poly(pyrrole-co-pyrrole propylic acid) film by electrochemical surface plasmon resonance

Poly(pyrrole-co-pyrrole propylic acid) (PPy/PPa) composite films were prepared for the first time by electrochemical copolymerization in mixed pyrrole propylic acid (Pa) and pyrrole solutions. The electrochemical growth process was investigated by in situ electrochemical surface plasmon resonance (ESPR). Atomic force microscopy and Fourier transform infrared spectroscopy were applied to characterize the prepared films. Using bovine serum albumin as a model protein, the adsorption kinetics of the protein on PPy/PPa films were studied in situ by SPR. The composition of Pa, the isoelectric point of proteins, the pH of buffers, and surfactant treatment showed dramatic effects on the protein adsorption on the PPy/PPa film. Experimental results indicated that the electrostatic interaction between the PPy/PPa film and proteins plays a critical role in protein adsorption and provided a novel strategy to efficiently immobilize proteins and to reduce nonspecific bindings of proteins in an immunobiosensor.     

Conformational dynamics of poly(acrylic acid). A study using surface plasmon resonance spectroscopy

The conformational dynamics of poly(acrylic acid) induced by pH change is reported here. Poly(acrylic acid) immobilized on gold surface was exposed to pH changes, and the conformational changes thus induced were followed in real time using surface plasmon resonance spectroscopy. The temporal profile of the stretching-coiling phenomenon showed a minimum point, which was proposed to be arising due to the contradictory behavior of two different property changes in the polymeric system. Normally surface plasmon resonance (SPR) response would be a convoluted effect of the thickness and refractive index changes, but the behavior observed here, where the SPR response is predominantly governed by either one of the two, is unique and to the author's knowledge is a feature that is observed for the first time. Analysis of the kinetics of the angle change revealed that it takes longer for the polymer to stretch than it takes for it to collapse, with the kinetic rate constants varying by at least an order of magnitude. The SPR angle change as well as the kinetic constants increased linearly with molecular weight. Effect of Ca2+ was studied, and it was found that the polymer was locked in its conformation due to the binding of the multivalent cations.     

Localized surface plasmon resonance sensing detection of glucose in the serum samples of diabetes sufferers based on the redox reaction of chlorauric acid

In this paper, the formation of gold nanoparticles (Au NPs) as a result of the thermo-active redox reaction of chlorauric acid (HAuCl₄) and glucose in alkaline medium was identified by measuring the plasmon resonance absorption, localized surface plasmon resonance (LSPR), and transmission electron microscopy (TEM) images, for the formation of Au NPs displays characteristic plasmon resonance absorption bands and corresponding LSPR signals. It was found that the resulted LSPR signals could be easily detected with a common spectrofluorometer. With increasing glucose concentration, the LSPR intensity displays linear response with the glucose content over the range from 2.0 to 250.0 μmol l⁻¹. Thus, a novel assay of glucose was established with the limits of determination (3σ) being 0.21 μmol l⁻¹, and the detection of glucose could be made easily in the serum samples of diabetes sufferers. Mechanism investigations showed that the activation energy and molar ratio of the reaction were 34.8 kJ mol⁻¹ and 3:2, respectively.     

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.     

Electrochemical synthesis of polyaniline in surface-attached poly(acrylic acid) network, and its application to the electrocatalytic oxidation of ascorbic acid

Acrylic acid was first electropolymerized on the surface of a gold electrode. Then, polyaniline (PANI) was electrodeposited on the poly(acrylic acid) (PAA) network to give a PANI–PAA composite film. Scanning electron microscopy and electrochemical studies confirmed the formation of PANI–PAA composite which exhibited excellent electroactivity over a wide pH range. The electro-oxidation of ascorbic acid (AA) was studied in detail. The modified electrode exhibits significantly reduced oxidation overpotential. The response towards AA is linear in the range 1.0 μM to 9.3 mM (R?=?0.9997, n?=?33) at a potential of 0.1 V (vs. SCE). The sensitivity is 207 μA mM^-1 cm^-2, and the detection limit is 1.0 μM (S/N?=?3). Interferences by uric acid and dopamine are negligible. The electrode thus enables sensitive and selective determination of AA, with a performance superior to many other PANI–based ascorbate sensors.     

Application of differential electrochemical mass spectrometry to the electrocatalytic oxidation of formic acid at a modified Bi/Pt electrode surface

Ohne Zusammenfassung     

Kappa-casein based electrochemical and surface plasmon resonance biosensors for the assessment of the clotting activity of rennet

We report for the first time the development of kappa-casein (κ-CN)-based electrochemical and surface plasmon resonance (SPR) biosensors for the assessment of the clotting activity of rennet. Electrochemical biosensors were developed over gold electrodes modified with a self-assembled monolayer of dithiobis-N-succinimidyl propionate, while SPR measurements were performed on regenerated carboxymethylated dextran gold surfaces. In both types of biosensor, κ-CN molecules were immobilized onto modified gold surfaces through covalent bonding. In electrochemical biosensors, interactions between the immobilized κ-CN molecules and chymosin (the active component of rennet) were studied by performing cyclic voltammetry, differential pulsed voltammetry, and electrochemical impedance spectroscopy (EIS) measurements, using hexacyanoferrate(II)/(III) couple as a redox probe. κ-CN is cleaved by rennet at the Phe105–Met106 bond, producing a soluble glycomacropeptide, which is released to the electrolyte, and the positively charged insoluble para-κ-casein molecule, which remains attached to the surface of the electrode. This induced reduction of the net negative charge of the sensing surface, along with the partial degradation of the sensing layer, results in an increase of the flux of the redox probe, which exists in the solution, and consequently, to signal variations, which are associated with the increased electrocatalysis of the hexacyanoferrate(II)/(III) couple on the gold surface. SPR experiments were performed in the absence of the redox probe and the observed SPR angle alterations were solely attributed to the cleavage of the immobilized κ-CN molecules. Various experimental variables were investigated and under the selected conditions the proposed biosensors were successfully tried to real samples. The ratios of the clotting power units in various commercial solid or liquid samples, as they are calculated by the EIS-based data, were almost identical to those obtained with a reference method. In addition, EIS measurements showed an excellent reproducibility, lower than 5%.     

Enhanced interlayer interaction in cellulose single nanofibre and poly(l-lactic acid) layered films by plasma-initiated surface grafting of poly(acrylic acid) onto poly(l-lactic acid) films

The surface of a poly(l-lactic acid) (PLLA) film was modified with poly(acrylic acid) (PAA) by plasma-initiated polymerization to increase the interaction between PLLA and cellulose single nanofibres (CSNF). The surface wettability of the PAA grafted PLLA film (PLLA-PAA film) was investigated by contact angle measurements. Modification of the PLLA film with PAA decreased the contact angle from 61° to 50°. The surface morphologies of the PLLA film, PLLA-PAA film and CSNF-coated PLLA-PAA film were studied by atomic force microscopy. The interaction between the CSNF and PLLA layers was strengthened by incorporation of a PAA layer onto the PLLA films and it is higher than 2N as proved by a peeling test. This is probably because the carboxyl groups of PAA form hydrogen bonds with the hydroxyl groups of CSNF.     

Direct electrochemical oxidation of a pesticide, 2,4-dichlorophenoxyacetic acid,at the surface of a graphite felt electrode: Biodegradability improvement

Pesticides’ biorecalcitrance can be related to the presence of a complex aromatic chains or of specific bonds, such as halogenated bonds, which are the most widespread. In order to treat this pollution at its source, namely in the case of highly concentrated solutions, selective processes, such as electrochemical processes, can appear especially relevant to avoid the possible generation of toxic degradation products and to improve biodegradability in view of a subsequent biological mineralization. 2,4-D was found to be electroactive in oxidation, but not in reduction, and the absence of hydroxyl radicals formation during the electrochemical step was demonstrated, showing that the pretreatment can be considered as a “direct” electrochemical process instead of an advanced electrochemical oxidation process. The presence of several degradation products in the oxidized effluent showed that the pretreatment was not as selective as expected. However, the relevance of the proposed combined process was confirmed since the overall mineralization yield was close to 93%.     

Electrochemical oxidation of ochratoxin A at a glassy carbon electrode and in situ evaluation of the interaction with deoxyribonucleic acid using an electrochemical deoxyribonucleic acid-biosensor

Ochratoxin A (OTA) is a fungal metabolite that occurs in foods, beverages, animal tissues, human blood and presents carcinogenic, teratogenic and nephrotoxic properties. This study concerns the redox properties of OTA using electrochemical techniques which have the potential for providing insights into the biological redox reactions of this molecule. The in situ evaluation of the OTA interaction with DNA using a DNA-electrochemical biosensor is also reported.The oxidation of OTA is an irreversible process proceeds with the transfer of one electron and one proton in a diffusion-controlled mechanism. The diffusion coefficient of OTA was calculated in pH 7 phosphate buffer to be D_O = 3.65 × 10⁻⁶ cm² s⁻¹. The oxidation of OTA is also pH dependent for electrolytes with pH < 7 and involves the formation of a main oxidation product which adsorbs strongly at the GCE surface undergoing reversible oxidation. In alkaline electrolytes OTA undergoes chemical deprotonation, the oxidation involving only the transfer of one electron.The electrochemical dsDNA-biosensor was also used to evaluate the possible interaction between OTA and DNA. The experiments have clearly proven that OTA interacts and binds to dsDNA strands immobilized onto a GCE surface, but no evidence of DNA-damage caused by OTA was obtained.     

Specific features characterizing electrochemical synthesis of polyaniline conducted in the presence of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) and the spectroelectrochemical characteristics of the obtained films

The electrochemical matrix polymerization of aniline in the presence of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) is performed in conditions that lead to the formation of an interpolymer complex comprising polyaniline and PAMPSA of the 1: 2 composition. The acceleration of the process of polymerization of aniline in the presence of PAMPSA as compared with traditional electropolymerization of aniline in hydrochloric acid is caused by the association of aniline molecules with the sulfo groups of PAMPSA and by a high concentration of hydrogen ions in the vicinity of a molecule of PAMPSA. It is established for the first time ever that, in the initial stages of synthesis for both polymeric and low-molecular-weight acids, the rate of polymerization is substantially greater at a smaller concentration of the acid. The distinguishing feature of the initial stage of electropolymerization of aniline at a low acidity of the environment is a non-autocatalytic character of the process, which may exert a discernible influence on a complex of physicochemical properties of polyaniline, including electric conduction. Studying spectroelectrochemical properties of the obtained films shows practical identity of their spectra with the spectra of standard polyaniline.     

In situ electro-deposition of Pt micro-nano clusters on the surface of {[PMo12O40]3-/PAMAM}n multilayer composite films and their electrocatalytic activities regarding methanol oxidation

The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films are prepared by LBL electrostatic assembly technique, and their uniform and homogeneous traits have been verified by cyclic voltammetry. The {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films with PAMAM as the outmost layer, having an open structure and exhibiting good penetrability for the solvent molecules at low pH, are used as matrices for electro-deposition of Pt micro-nano clusters in situ. X-ray photoelectron spectroscopy (XPS) analysis and field emission scanning electron microscope (FE-SEM) characterization show that the unique Pt micro-nano clusters with flower-like structure have been immobilized on the surface of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. The morphologies of Pt micro-nano clusters are influenced by electro-deposition conditions such as deposition potential, deposition time, and the number of layers of {[PMo(12)O(40)](3-)/PAMAM}(n) multilayer films. Pt(-clusters)-{PMo(12)/PAMAM}(3) composite films demonstrate good electrocatalytic activities regarding methanol oxidation and improved tolerance of CO.     

An easy electrochemical procedure for tailoring thin films containing the [Fe(bpy)2(CH3CN)2] and/or [Fe(bpy)3]-like cores (bpy=2,2-bipyridine). Application to the design of a modified electrode with a supramolecular structure

A simple electrochemical procedure to tailor thin polymeric films containing the [Fe^II(bpy)₂(CH₃CN)₂]²⁺ and/or [Fe^II(bpy)₃]²⁺-like cores have been described (bpy=2,2^′-bipyridine). The procedure is based on the electroreductive precipitation of soluble polymers prepared in situ in CH₃CN by mixing Fe³⁺ ions and a bis bipyridyl ligand, (chiragen: chir). In the resulting [Fe^II(chir)(CH₃CN)₂]_n²⁺ films, the two labile S ligands can be easily replaced by a bidentate ligand. This method has been applied with success to design a modified electrode with a supramolecular structure.