Ewa Rozniecka

Hydrophobic silica sol–gel films for biphasic electrodes and porotrodes

Hydrophobic sol-gel films from methyltrimethoxysilane (MTMOS) are deposited onto glass and tin-doped indium oxide (ITO) coated glass substrates. Uniform and microporous films of ca. 200 nm thickness are obtained and investigated by scanning electron microscopy and by electrochemical techniques. From cyclic voltammograms for the oxidation of ferrocenedimethanol in aqueous 0.1 M KNO3 apparent diffusion coefficients and free volume data for processes within the film are derived and it is demonstrated that the film morphology can be controlled by the deposition timing. Two novel types of biphasic electrodes for observing liquid/liquid ion transfer reactions are introduced: (i) an ITO electrode coated with a hydrophobic sol-gel film and (ii) a hydrophobic sol-gel film on glass sputter-coated with 20 nm porous gold (porotrode). For the t-butylferrocene redox system deposited in the form of an organic liquid, very low and morphology dependent current responses are observed on modified ITO electrodes. However, the porotrode system allows biphasic electrode reactions to be driven with high efficiency and with no significant morphology effect of the hydrophobic sol-gel film. This type of nanofilm-modified electrode system will be of interest for biphasic sensor developments.

Electrochemical determination of selected neurotransmitters at electrodes modified with oppositely charged carbon nanoparticles

The electrocatalytic oxidation of neurotransmitters on the electrodes modified with oppositely charged carbon nanoparticles has been investigated. These nanoparticles were deposited at the electrode from the aqueous suspensions via a layer-by-layer method. The electrocatalytic response was evaluated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. The modified electrode exhibited good electrocatalytic properties towards not only dopamine oxidation, but also for epinephrine and serotonin oxidation. This allows us to separate their voltammetric signals from the signals of interfering substances such as ascorbic acid or uric acid. The obtained calibration curves are in the range 0.4–350 μM, 1–49 μM and 0.8–100 μM with detection limits of 0.4 μM, 1.0 μM and 0.8 μM for dopamine, epinephrine and serotonin, respectively. In addition these carbon nanoparticulate electrodes showed excellent sample to sample reproducibility (the relative standard deviations for n = 7 equal 0.7%) and, maintained 94% of electrochemical signal corresponding to dopamine oxidation after 18 month storage.

Stack of Nano-Films on Optical Fiber End Face for Label-Free Bio-Recognition

This paper presents a study on sensing capabilities of stacks of nano-films deposited on a single-mode optical fibers end face for application in label-free bio-recognition. The stack consist of five nano-films of periodically interchanging materials characterized by different refractive indices (n at λ = 1550 nm), aluminum AlxOy (n ~ 1.58 RIU) and titanium TiOx (n ~ 2.42 RIU) oxides layers. The stack was deposited with the reactive magnetron sputtering technique. It has been found that the structures show sensitivity to refractive index of surrounding liquid (74.4 nm/RIU and 44.3 dBm/RIU) and negligible sensitivity to variations of temperature. Moreover, we show that these structures when functionalized can be used for selective detection of biological layer formation on their surface. In this study, a biotin-avidin complex was used to show a label-free bio-recognition capability of the approach. Avidin concentration of 1 mg/ml induced shift of the resonance wavelength and change in reflected power by 3 nm and 0.8 dBm, respectively, when BSA, which is nonspecific to biotin, resulted in a negligible change in spectral response. The approach seems to be very interesting, especially when such advantages as batch device fabrication, sensor robustness, and fully automatized stack deposition process are taken into account.