RESUMEN
The possibility of using a single electroactive and luminescent molecule both as a redox mediator and as a fluorophore in an experiment combining in situ Scanning Electrochemical Microscopy (SECM) and epifluorescence microscopy was validated. The usual working modes of SECM, namely positive and negative feedback as well as generation-collection, were used and the fluorescence images, intensity and spectra were recorded for each configuration. The tip potential, tip-substrate distance and, in the case of a conducting substrate, the substrate potential are the parameters that are likely to control the fluorescence. It is shown that the tip can be used to switch on and off the luminescence and that the modulation amplitude maximum is sensitive to the nature of the substrate. Approach curves based on this fluorescence modulation amplitude can be obtained showing a higher sensitivity than the classical electrochemical ones.
RESUMEN
A very sensitive technique where an electrochemical cell is coupled to a total internal reflection fluorescence microscopy setup is described and applied for the first time to the electrochemical monitoring of the fluorescence of organic dyes in solution. It is shown that this setup basically allows both spatial and time resolution for the recorded fluorescence signal as a function of the electrode potential: indeed the variations of the emission intensity are recorded within the diffusion layer for a classical cyclic voltammetry or chronoamperometry experiment inducing the redox conversion of an emissive form into a non emissive one (and conversely). Simultaneously, the variations of the emissive state lifetime are measured to discriminate between a mechanism involving only the conversion into a non emissive form from one involving a quenching between the emitter and the electrogenerated species. The results concerning the investigation of the electrochemical monitoring of the fluorescence properties for two types of original dyes are presented, demonstrating the possibility to switch on and off the emission in a fully reversible way and to investigate in depth the mechanisms associated to this switch.
Asunto(s)
Electroquímica/instrumentación , Colorantes Fluorescentes/análisis , Colorantes Fluorescentes/química , Microscopía Fluorescente/instrumentación , Diseño de Equipo , Análisis de Falla de EquipoRESUMEN
A direct route to silica-polypyrrole core-shell nanoparticles has been used to design new nanocomposites, in which the conducting part is then wrapped by an external silica shell in order to have finally neutral nanoparticles. The nanocomposites are characterized by TEM, spectroscopy, electrochemistry and thermal gravimetric analysis, demonstrating that the external silica shell actually insulates the conjugated polymer from the outer medium. Finally the electrorheological properties of these nanocomposites are checked in a dielectrophoretic device in which the motion of the particles induced by an external electric field can be used to monitor a switch of the light transmission properties.
Asunto(s)
Nanocompuestos/química , Nanotecnología/métodos , Reología/métodos , Electroquímica/métodos , Diseño de Equipo , Microscopía Electrónica de Transmisión , Conformación Molecular , Nanoestructuras/química , Polímeros/química , Pirroles/química , Dióxido de Silicio/química , Espectroscopía Infrarroja por Transformada de Fourier , Termogravimetría , Rayos UltravioletaRESUMEN
New xerogels functionalized by ferrocenes as redox probes have been prepared using various types of catalysis. The analysis of the electrochemical response in the case of modified electrodes allows us to get an insight into the gel nanostructure which has been found to be isotropic in the case of acidic catalysis, and fractal in the case of fluoride catalysis, provided that the amount of functionalized silanes is not too high. Indeed the results of electrochemical measurement prove that the fractality of functionalized hybrid silica is general in the case of basic catalysis, except in the case of very high functional moieties loading, where the electrode become essentially organic and isotropic. On the other hand, in the case of acidic catalysis, whatever the amount of organic material, the hybrid gel remains isotropic, and a classical electron pseudo-diffusive behaviour is observed. The diffusion coefficient values extracted from the current-time slopes do not vary monotonically with the amount of redox probe in the case of fractal xerogel structures, which is indicative that not all the functional moieties are electroactive in that case.
Asunto(s)
Electrodos , Compuestos Ferrosos/química , Fractales , Silicatos/química , Electroquímica , Geles , MetalocenosRESUMEN
Using an original protocol with a rotating gel electrophoresis apparatus, it is shown that duplex DNA undergoing crossed-field electrophoresis in agarose gets trapped in the gel when the field is increased above a threshold value which decreases with the chain length and depends on the angle between the fields in a non-monotonous manner. This trapping is irreversible, i.e. once trapped at a high field strength, chains are unable to resume their motion when the field is returned to a lower value at which they moved prior to trapping. A model of trapping by "tight knots" is proposed. It predicts a trapping threshold proportional to the inverse square of the electric field, in qualitative agreement with the data. The implications of our results for the separation of large DNA molecules are discussed.