Electrochemic properties of single-wall carbon nanotube electrodes

The electrochemical properties of single-wall carbon nanotube ~CNT! electrodes in the form of sheets or papers have been examined. Thermal annealing has produced significant changes in a range of properties of the material including increased hydrophobicity and elimination of electroactive surface functional groups and other impurities. As a result of these changes, the treated electrodes exhibit lower double-layer capacitance, absence of faradaic responses and associated pseudocapacitance, and a better frequency response. The basic electrochemical behavior of the CNT paper electrodes is not markedly affected by relatively large differences in electrolyte ion size, consistent with an average pore size of 9 nm. Increases in both CNT sheet thickness and surface area induce a slower electrode response in agreement with the porous nature of the electrode matrix

Electrochemical Characterization of Single-Walled Carbon Nanotube Electrodes

The cyclic voltammetric responses and capacitive behavior of single-walled carbon nanotube sheets or papers are described. Broad redox responses have been observed in aqueous solutions that are probably due to the presence of oxygen-containing groups bound to the surface of the nanotubes or to the impurities produced during nanotube purification. The voltammetry and capacitance of the nanotube paper do not vary significantly when the chemical nature of the electrolyte ions is changed. In nonaqueous media, no redox responses are produced except in solutions of Li1, where an intense reduction response, possibly due to lithium insertion into the nanotube bundles, is observed. Electrochemical impedance spectroscopy in aqueous solutions reveals the typical features associated with a porous material. Electrochemical quartz crystal microbalance studies in both aqueous and nonaqueous electrolytes show that the mass of the nanotube film increases as the potential is made more negative. These mass changes are affected by, but are not directly proportional to, the cation mass. In acetonitrile solutions of Li1, a significant increase in mass associated with the suggested insertion of the cation is observed

ATR-IR spectroscopic studies of the influence of phosphate buffer on adsorption of immunoglobulin G to TiO2

In situ attenuated total reflectance infrared (ATR-IR) spectroscopy has been applied to the study of the influence of phosphate on the extent of protein adsorption onto TiO2. Immunoglobulin G (Ig.G) was adsorbed onto a TiO2 sol–gel film from solutions containing phosphate or NaCl. Monitoring of the amide II absorbance (v=1545 cm−1) confirmed reduced protein adsorption from the phosphate containing solution. In situ ATR-IR spectroscopy was also used to study phosphate induced desorption of Ig.G. Solutions containing various phosphate concentrations were passed over a TiO2 film with Ig.G adsorbed to it. As the concentration of phosphate increased the amide II absorbance decreased confirming the removal of bound Ig.G from the TiO2 surface. As the amide II absorbance decreased the phosphate absorbance (v=1080 cm−1) increased suggesting accumulation of phosphate at the TiO2 surface. Not all of the bound protein could be displaced from the TiO2 surface by phosphate suggesting the presence of weakly and strongly bound Ig.G

Characterisation of olive oil by an electronic nose based on conducting polymer sensors.

The selection and test of an array of conducting polymer sensors with extra-virgin olive oil samples is presented in this paper as a first step towards the development of an electronic nose dedicated to the detection of olive oil aroma. Different sensors produced by both electrochemical and chemical techniques were initially exposed to a set of pure substances present in the headspace of extra-virgin olive oil and meaningful for the evaluation of its overall organoleptic characteristics. Four sensors showing the best sensitivity to these standard substances were chosen to carry out further experiments on samples of commercial olive oil. Two different experimental set-ups and protocols for olive oil sampling were tested and compared, providing evidence on the best procedure needed to handle this foodstuff and on the possibility of using a dedicated sensing system for practical purposes in the olive oil industry. Three different extra-virgin Italian types of olive oil can be easily distinguished with an array of four sensors and it is also possible to detect changes in the aromatic content of the headspace after handling of the samples. Different samples of the same oil show reproducible responses

Studies of double layer capacitance and electron transfer at a gold electrode exposed to protein solutions

Electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical behaviour of a gold electrode exposed to proteins prepared in phosphate buffer. Exposure to solutions of human serum albumin (HSA) and immunoglobulin G (Ig.G) resulted in a decrease of the double layer capacitance (Cdl) and an increase in the charge transfer resistance (Rct) at the gold electrode solution interface. The greatest capacitance decrease for both proteins was observed when exposure occurred at or more positive to the electrode open circuit potential (OCP). Exposure to Ig.G resulted in a greater decrease in capacitance as compared to HSA under identical conditions. These capacitance and charge transfer resistance variations were attributed to the formation of a proteinaceous layer on the electrode surface during exposure

Investigation of protein adsorption and electrochemical behavior at a gold electrode

The adsorption of two model proteins, human serum albumin and immunoglobulin G, on a gold electrode surface was investigated using 125I radiolabeling and cyclic voltammetry (CV). 125I radiolabeling was used to determine the extent of protein adsorption, while CV was used to ascertain the effect of the adsorbed protein layer on the electron transfer between the gold electrode and an electroactive moiety in solution, namely, K3Fe(CN)6. The adsorbed amounts of HSA and IgG agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential (700 mV) was applied to the electrode, while the application of a negative potential (−800 mV) resulted in a decrease. When the solution pH was varied to alter the charge on the protein, the adsorption trends appeared to follow electrostatic interaction, namely, greater adsorption when the electrode and the protein possessed opposite charge and vice versa. The adsorbed protein layer had the effect of blocking the electron transfer. It was possible to correlate the degree of electron blocking with the amount of adsorbed protein to show that the greater the adsorption, the larger the blocking effect. Of the two proteins used, HSA proved to be more efficient at blocking the electron transfer