Cecilia Bonazzola

Methylene Blue Incorporation into Alkanethiol SAMs on Au(111): Effect of Hydrocarbon Chain Ordering

A detailed polarization modulation infrared reflection absorption spectroscopy, scanning tunneling microscopy, and electrochemical study on methylene blue (MB) incorporation into alkanethiolate self-assembled monolayers (SAMs) on Au(111) is reported. Results show that the amount of MB incorporated in the SAMs reaches a maximum for intermediate hydrocarbon chain lengths (C10-C12). Well-ordered SAMs of long alkanethiols (C > C12) hinder the incorporation of the MB molecules into the SAM. On the other hand, less ordered SAMs of short alkanethiols (C < or = C6) are not efficient to retain the MB incorporated through the defects. For C12 the amount of incorporated MB increases as the SAM disorder is increased. This information is essential to the design of efficient thiol-based Au vectors for transport and delivery of molecules as well as thiol-based Au devices for molecular sensing.

An electrochemical impedance and spectroelectrochemical study of the polypyrrole–flavin composite electrode

Electrodes modified with polypyrrole–flavin mononucleotide composite film (PPy–FMN) have been studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and UV-visible spectro-electrochemistry with optically transparent electrodes (OTE). Flavin molecules, electrostatically trapped in the composite film, act as dopant anions and can be reduced chemically by reduced PPy0 or electrochemically with a conducting PPy backbone connecting them to the underlying electrode. Both the electrochemistry and the electronic spectra of FMN entrapped in the PPy film markedly differ from those of FMN in aqueous solutions. These differences arise from the interactions of flavin molecules in a rigid matrix and the possibility of both chemical reduction of FMN by reduced PPy0 and flavin electro-reduction in the host polymer matrix.

Electrochemical fluorescence modulation at a redox hydrogel modified electrode

Electrochemical fluorescence modulation of flavin redox centers covalently attached to a poly(allylamine)-hydrogel modified ITO electrode was achieved by faradaic modulation of redox states. At least a fraction of the fluorescent flavins is electroactive. Redox switching between oxidised flavin and non-fluorescent reduced leucoflavin was monitored by square wave modulated and linear scan voltfluorometry. Differential cyclic voltfluorograms and cyclic voltammograms are in very good agreement. In situ fluorescence spectroscopy can be applied to complement electrochemical studies of redox-dyes incorporated in polymeric matrices attached to the electrode surface. Advantages of electrochemical modulated fluorescence in these systems are enhanced sensitivity and selectivity in bio-sensors and the ability to obtain an insight into dynamic electron transfer processes.