A new amperometric nanostructured sensor for the analytical determination of hydrogen peroxide

A new amperometric, nanostructured sensor for the analytical determination of hydrogen peroxide is proposed. This sensor was constructed by immobilizing silver nanoparticles in a polyvinyl alcohol (PVA) film on a platinum electrode, which was performed by direct drop-casting silver nanoparticles that were capped in a PVA colloidal suspension. UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy were used to give a complete characterization of the nanostructured film. Cyclic voltammetry experiments yielded evidence that silver nanoparticles facilitate hydrogen peroxide reduction, showing excellent catalytic activity. Moreover, the cronoamperometric response of modified sensors was dependent on nanoparticle lifetime. Experiments were performed, using freshly prepared solutions, after 4 and 8 days. Results concerning the quantitative analysis of hydrogen peroxide, in terms of detection limit, linear range, sensitivity and standard deviation (STD), are discussed for each tested sensor type. Utilization of two different linear ranges (40 microM to 6mM and 1.25 microM to 1.0mM) enabled the assessment of concentration intervals having up to three orders of magnitude. Moreover, the electrode made using a 4-day-old solution showed the maximal sensitivity of 128 nA microM(-1)(4090 nA microM(-1)cm(-2)), yielding a limit of detection of 1 microuM and STD of 2.5 microAmM(-1). All of these analytical parameters make the constructed sensors suitable for peroxide determination in aqueous solution.     

Evaluation of electrochemically synthesized sulfadimethoxine‐imprinted polymer for solid‐phase microextraction of sulfonamides

Solid‐phase microextraction (SPME) is widely used in analytical laboratories for the analysis of organic compounds, thanks to its simplicity and versatility. In the present work, the synthesis and evaluation of imprinted films for SPME by electropolymerisation of pyrrole alone or in the presence of ethylene glycol dimethacrylate is proposed. Sulfadimethoxine (SDM), a sulfonamide antibiotic, was used as template molecule. Initially, a molecularly imprinted polymer film was prepared by electropolymerisation of pyrrole onto a platinum foil, using SDM as template. The SDM template was removed by overoxidation. The behaviour of SDM on imprinted and non‐imprinted polymers was investigated by differential pulse voltammetry, and a clear imprinting effect was observed, which was confirmed by rebinding experiments using both conventional and electrochemically enhanced‐SPME. However, in general, the extraction efficiency was rather low (<6%) and unspecific interactions are too high. Attempts to increase extraction efficiency were unsuccessful, but the incorporation of ethylene glycol dimethacrylate to the films reduced unspecific interactions to a certain extent. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a sensor prepared by entrapment of MIP particles in electrosynthesised polymer films for electrochemical detection of ephedrine

A voltammetric sensor for (-)-ephedrine has been prepared by a novel approach based on immobilisation of an imprinted polymer for ephedrine (MIPE) in an electrosynthesised polypyrrole (PPY) film. Composite films were grown potentiostatically at 1.0 V vs. Pt (QRE) on a glassy carbon electrode using an unconventional "upside-down" (UD) geometry for the three-electrode cell. As a consequence, a high MIP loading was obtained, as revealed by SEM. The sensor response was evaluated, after overoxidation of PPY matrix, by cyclic voltammetry after pre-concentration in a buffered solution of analyte in 0.5-3 mM concentration range. An ephedrine peak at approximately 0.9 V increasing with concentration and saturating at high concentrations was evident. PPY-modified electrode showed a response, which was distinctly lower than the MIP response for the same concentration of the template. The effect of potential interferences including compounds usually found in human fluids (ascorbic acid, uric acid, urea, glucose, sorbitol, glycine, dopamine) was examined.     

Development and characterization of a novel bioactive polymer with antibacterial and lysozyme‐like activity

The development and characterization of a novel bioactive polymer based on the immobilization of glucose oxidase enzyme (GOx) in a polyvinyl alcohol (PVA) film showing antibacterial activity is presented. The PVA‐GOx composite material was extensively characterized by UV‐vis, X‐ray Photoelectron (XPS) spectroscopy and by Fourier Transform Infrared (FTIR) spectroscopy to verify the preservation of enzyme structural integrity and activity. The antimicrobial activity of this composite material against Escherichia coli and Vibrio alginolyticus was assessed. Furthermore the lysozyme‐like activity of PVA‐GOx was highlighted by a standard assay on Petri dishes employing Micrococcus lysodeikticus cell walls. The findings from this study have implications for future investigations related to the employment of PVA‐GOx system as a composite material of pharmaceutical and technological interest. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 461–470, 2014.     

Low-potential sensitive H2O2 detection based on composite micro tubular Te adsorbed on platinum electrode

In this work a new original amperometric sensor for H(2)O(2) detection based on a Pt electrode modified with Te-microtubes was developed. Te-microtubes, synthesized by the simple thermal evaporation of Te powder, have a tubular structure with a hexagonal cross-section and are open ended. Modified electrode was prepared by direct drop casting of the mixture of Te-microtubes dispersed in ethanol on Pt surface. The spectroscopic characterization of synthesized Te-microtubes and Pt/Te-microtubes modified electrodes was performed by scanning electron microscopy (SEM), energy-dispersive X-rays microanalysis (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). Moreover a complete electrochemical characterization of the new composite material Pt/Te-microtubes was performed by cyclic voltammetry (CV) and cronoamperometry (CA) in phosphate buffer solution (PBS) at pH 7. Electrochemical experiments showed that the presence of Te-microtubes on modified electrode was responsible for an increment of both cathodic and anodic currents in presence of H(2)O(2) with respect to bare Pt. Specifically, data collected from amperometric experiments at -150 mV vs. SCE in batch and -200 mV vs. SCE in flow injection analysis (FIA) experiments show a remarkable increment of the cathodic current. The electrochemical performances of tested sensors make them suitable for the quantitative determination of H(2)O(2) substrate both in batch and in FIA.     

Piezoelectric sensor functionalised by a self-assembled bipyridinium derivative: characterisation and preliminary applications in the detection of heavy metal ions

The synthesis of a molecule, 1-(11-dodecylsulfanyl-undecyl)-[4,4']bipyridinium bromide (1), suitable at the same time to form a covalent bond with gold electrodes of a piezoelectric quartz crystal and to interact with heavy metal ions in aqueous solutions, has been successfully accomplished. A commercial quartz crystal microbalance instrument has been modified in order to perform a Flow-Injection Analysis. The behaviour of the system follows the Kanazawa-Gordon equation as demonstrated by measurements with glucose solutions. The self-assembled layer of 1 onto a gold electrode has been characterised by Atomic Force Microscopy before and after the sensing tests. The sensing performances of the modified gold electrode were investigated by monitoring the frequency variation induced by the presence of heavy metal ions, such as lead, cadmium and mercury, in aqueous media. The explored concentrations ranged between 10(-4) and 10(-2) M and the corresponding frequency variations ranged between 10 and 50 Hz. All responses observed were fast, reproducible and reversible. In particular, the response to mercury appears significantly higher in comparison with the other analytes. To the best of our knowledge, this contribution represents the first example of sensing layer based on bipyridinium receptor showing reversible and, at some extent, differentiated response towards heavy metal ions.     

Heavy metal determination by biosensors based on enzyme immobilised by electropolymerisation

The work describes the original application of biosensors based on enzyme immobilised by electropolymerisation to heavy metal determination. An inhibition detection scheme has been employed for detecting Hg2+ by an established glucose biosensor based on glucose oxidase immobilised in poly-o-phenylenediamine. The investigated enzymatic inhibition appears reversible and mixed, in agreement with data for the enzyme in solution. A low response time (<2 min) and a rapid recovery of response by EDTA seem the most interesting characteristics of the proposed biosensor at the present stage of development, along with the well known easy preparation of this kind of biosensors. The occurrence of a high response also for Cu2+ opens the possibility to apply the biosensor in total toxic metal content determination.