Paolo Bertoncello

Nanostructured materials for electrochemiluminescence (ECL)-based detection methods: Recent advances and future perspectives

This review presents a general picture of the last advances and developments (2003-2008) related to novel nanostructured materials for electrochemiluminescence-based biosensors using. It briefly covers the basic mechanisms of ECL detection, and the recent developments in fabrication of solid-state ECL sensors using nanostructured materials such as carbon nanotubes, metal nanoparticles, quantum dots, thin films of metallopolymers and of inorganic metal complexes. Finally, challenges and perspectives of the use of such materials for biomedical diagnostics are discussed.

Cholesterol biosensors prepared by layer-by-layer technique.

The analysis of formation, deposition and characterization of cholesterol oxidase (COX) layer-by-layer films were performed. Initially, a layer of polyanion, poly(styrene sulfonate) (PSS) was adsorbed followed by a layer of polycation, poly(ethylene imine) (PEI) on each solid substrate from aqueous solutions. The alternating layers were formed by consecutive adsorption of polycations (PEI) and negatively charged proteins (COX) and cholesterol esterase (CE). A strong interaction between protein and polyelectrolyte improves the stability of the alternating multilayer; however, it can change a native protein conformation and impair the protein activity. The PSS/PEI/COX, PSS/PEI/COX/PEI/CE, PSS/PEI/COX-CE/PEI etc. layered structures were prepared on the surface of a platinum electrode, ITO coated glass plate, quartz crystal microbalance, quartz plates, mica and silicon substrates. Optical and gravimetric measurements based on an ultraviolet-visible absorption spectroscopy and a quartz crystal microbalance revealed that the enzyme multilayers thus prepared consist of molecular layered of the proteins. The surface morphology of such bilayer films was investigated by using atomic force microscopy. The electrochemical redox processes of the enzyme-layered films deposited either on platinum or ITO coated glass plate were investigated. The response current of cholesterol oxidase electrode with concentration of cholesterol was investigated at length.

Determination of Trace Mercury in Saltwaters at Screen-Printed Electrodes Modified with Sumichelate Q10R

The results of a study on the determination of trace levels of mercury in natural saltwaters using screen-printed carbon electrodes modified with Sumichelate Q10R, a chelating resin containing dithiocarbamate groups, which binds mercury strongly and selectively are reported. Cyclic voltammetric measurements indicate that mercury(II) is preconcentrated by complexation at the modified electrode, giving peak currents which are about one order of magnitude higher than those obtained at an unmodifed screen-printed electrode. The voltammetric pattern is characterized by a broad reduction peak to which a sharp and well-resolved reoxidation peak is associated. Trace (subnanomolar) concentrations of mercury can be determined at the screen-printed modified electrode by adopting a complexation-anodic stripping procedure with detection via differential pulse voltammetry. The method is characterized by a low detection limit (3j blank/sensitivity) of 12 pM with 20 min complexation and 5 min reduction at ‐0.5 V. Excess copper interferes in the analysis of mercury only when present in more than hundred-fold excess. Data concerning the application of modified screen-printed electrodes to the analysis of mercury in water samples from the channels of Venice (Italy) are presented and discussed.

Analytical applications of nanomaterials in electrogenerated chemiluminescence

This critical review covers the use of carbon nanomaterials (single-wall carbon nanotubes, multi-wall carbon nanotubes, graphene, and carbon quantum dots), semiconductor quantum dots, and composite materials based on the combination of the aforementioned materials, for analytical applications using electrogenerated chemiluminescence. The recent discovery of graphene and related materials, with their optical and electrochemical properties, has made possible new uses of such materials in electrogenerated chemiluminescence for biomedical diagnostic applications. In electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), electrochemically generated intermediates undergo highly exergonic reactions, producing electronically excited states that emit light. These electron-transfer reactions are sufficiently exergonic to enable the excited states of luminophores, including metal complexes, quantum dots and carbon nanocrystals, to be generated without photoexcitation. In particular, this review focuses on some of the most advanced and recent developments (especially during the last five years, 2010–2014) related to the use of these novel materials and their composites, with particular emphasis on their use in medical diagnostics as ECL immunosensors.

Electrochemiluminescence (ECL) sensing properties of water soluble core-shell CdSe/ZnS quantum dots/Nafion composite films

Water soluble positively charged 2-(dimethylamino)ethanethiol (DAET)-protected core-shell CdSe/ZnS quantum dots (QDs) were synthesized and incorporated within negatively charged Nafion polymer films. The water soluble QDs were characterized using UV-visible and fluorescence spectroscopies. Nafion/QDs composite films were deposited on glassy carbon electrodes and characterized using cyclic voltammetry. The electrochemiluminescence (ECL) using hydrogen peroxide as co-reactant was enhanced for Nafion/QDs composite films compared to films of the bare QDs. Significantly, no ECL was observed for Nafion/QDs composite films when peroxydisulfate was used as the co-reactant, suggesting that the permselective properties of the Nafion effectively exclude the co-reactant. The ECL quenching by glutathione depends linearly on its concentration when hydrogen peroxide is used as the co-reactant, opening up the possibility to use Nafion/QDs composite films for various electroanalytical applications.

Advances on scanning electrochemical microscopy (SECM) for energy

This review focuses on some of the recent advances on scanning electrochemical microscopy (SECM) applied to studies of heterogeneous chemical processes and chemical reactivity in materials involved in energy-related applications. The materials that are considered in the present review are mainly noble metals, metal coatings, and metal nanoparticles for electrochemical energy conversion systems such as fuel cells and batteries. In particular, the deposition of metal nanoparticles using SECM probes as well as studies of the chemical reactivity of noble metal nanoparticles for hydrogen evolution and hydrogen oxidation (HER and HOR, respectively), and oxygen evolution and reduction (OER and ORR, respectively) reactions are surveyed. Finally, this review will briefly describe some recent advances on the use of SECM as a novel tool for the investigation of electrocatalytic processes driven by enzymes for uses in biofuel cells.

Fabrication and characterization of poly[(2-methoxy-5-(2'-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV) Langmuir-Schaefer films and their application as photoelectrochemical cells

Abstract The Langmuir monolayer behaviour of poly[(2-methoxy-5-(2′-ethyl-hexyloxy)phenylene vinylene] (MEH-PPV) conducting polymer in a subphase containing various anions was investigated at the air–water interface. The Langmuir–Schaefer (LS) films were prepared in deionized water that showed the minimum area per molecule, and were found to be essential for the formation of Langmuir monolayer at the air–water interface of MEH-PPV conjugated polymer. The LS films of MEH-PPV were investigated by using UV–VIS absorption, electrochemical and atomic force microscopic techniques. A uniform deposition of monolayers was shown by optical technique, whereas a higher number of monolayers resulted in the tiny island morphology in MEH-PPV LS films. The influence of concentration of anions on the redox properties of the LS films was studied by cyclic voltammetric measurements. The nature of anions in electrochemical investigation revealed the significant changes in the redox properties of the MEH-PPV LS films. The photoelectrochemical current transient of MEH-PPV LS films was compared with those obtained by the solution cast technique. This work also focused on the influence of the nature of the electrolytes, the applied potential, the type of the film and the presence of dissolved oxygen on the photoelectrochemical properties of MEH-PPV conducting polymer.

Nanomaterials for biosensing with electrochemiluminescence (ECL) detection.

Analytical applications of nanomaterials used in electrochemiluminescence (ECL)-based detection methods are reviewed. Among nanomaterials, carbon-based nanomaterials (carbon nanotubes, graphene), metal nanoparticles, quantum dots, inorganic metal complexes and conducting polymers are considered. The most common mechanisms of ECL detections are also described in this review. Finally, challenges and perspectives of the use of such materials in chemical analysis are discussed.

Fabrication and physico-chemical properties of Nafion Langmuir–Schaefer films

The Langmuir monolayer behaviour of Nafion (perfluorinated ionomer) films at the air/water interface for different aqueous subphases was investigated. The pressure–area isotherms and the Brewster angle microscopic study of Langmuir monolayer of Nafion in different electrolytic media allowed us to find the best experimental conditions for the deposition of stable Langmuir–Schaefer (LS) films. The results obtained for Nafion LS films through a combination of physical measurements (UV–vis spectroscopy, atomic force microscopy and nano-gravimetry) indicated a stepwise and uniform growth of films on the substrate. The electrochemical and photoelectrochemical properties of dyes incorporated within Nafion LS films were investigated. This paper reports the first experimental results showing the possibility of obtaining and depositing Nafion LS films.

Preparation and voltammetric characterization of electrodes coated with Langmuir-Schaefer ultrathin films of Nafion®

Ultrathin films of Nafion® perfluorinated polymer were deposited on indium-tin oxide electrodes (ITO) by using Langmuir-Schaefer (LS) technique, after optimization of the subphase composition conditions. Morphological characteristics of these coatings were obtained by Atomic Force Microscopy (AFM). Nafion® LS films showed a good uniformity and complete coverage of the electrode surface, however a different organization degree of the polymer layer was evidenced with respect to thin films deposited by spin-coating. ITO electrodes modified with Nafion® LS coatings preconcentrate by ion-exchange electroactive cations, such as Ru[(NH3)6]3+, dissolved in diluted solutions. The electroactive species is retained by the Nafion® LS coated ITO also after transfer of the modified electrode into pure supporting electrolyte. This allowed the use of the ruthenium complex as voltammetric probe to test diffusion phenomena within the Nafion® LS films. Apparent diffusion coefficients (Dapp) of Ru[(NH3)6]3+ incorporated in Nafion® LS films were obtained by voltammetric measurements. Dapp values decrease slightly by increasing the amount of ruthenium complex incorporated in the ultrathin film. They are significantly lower than values typical for recasted Nafion® films, in agreement with the highly condensed nature of the Nafion® LS fims.