We investigate the dielectric properties of hydrogel by means of the impedance spectroscopy technique. Our experimental data relevant to the frequency dependence of the real and imaginary parts of the electrical impedance of the cell indicate that, in the low frequency region ͑f Ͻ 20 Hz͒, the electric response of the cell is dominated by surface effects, weakly dependent on the thickness of the sample. On the contrary, in the high frequency region ͑f Ͼ 100 Hz͒, the electric response of the sample is mainly due to the bulk properties. The observed frequency dependence of the electrical impedance of the cell can be well interpreted by means of the Poisson-Nernst-Planck model taking into account the Ohmic character of the interface electrodes-hydrogel.

The electric response of a hydrosolution is investigated. We show that our experimental data can be interpreted by means of the standard drift-diffusion model only if the frequency dependence of the viscosity of the hydrosolution is taken into account. From this result, it follows that measurements of impedance spectroscopy can give information on the non-newtonian character of complex fluids.

Nucleic-acid aptamers consisting in single-stranded DNA oligonucleotides emerged as very promising biorecognition elements for electrochemical biosensors applied in various fields such as medicine, environmental, and food safety. Despite their outstanding features, such as high-binding affinity for a broad range of targets, high stability, low cost and ease of modification, numerous challenges had to be overcome from the aptamer selection process on the design of functioning biosensing devices. Moreover, in the case of small molecules such as metabolites, toxins, drugs, etc., obtaining efficient binding aptamer sequences proved a challenging task given their small molecular surface and limited interactions between their functional groups and aptamer sequences. Thus, establishing consistent evaluation standards for aptamer affinity is crucial for the success of these aptamers in biosensing applications. In this context, this article will give an overview on the thermodynamic and structural aspects of the aptamer-target interaction, its specificity and selectivity, and will also highlight the current methods employed for determining the aptamer-binding affinity and the structural characterization of the aptamer-target complex. The critical aspects regarding the generation of aptamer-modified electrodes suitable for electrochemical sensing, such as appropriate bioreceptor immobilization strategy and experimental conditions which facilitate a convenient anchoring and stability of the aptamer, are also discussed. The review also summarizes some effective small molecule aptasensing platforms from the recent literature.

The permanent structure induced by an Ar þ linearly polarised laser beam on an asymmetric dye-doped nematic liquid crystal cell was investigated in a pump-probe experiment. The polarisation direction of the probe beam was parallel to the easy axis and two configurations of pump beam were used: polarisation directions perpendicular and parallel to the easy axis. The transmitted intensity of the probe beam was recorded during irradiation and it was observed that it depended both on the power and polarisation direction of the pump beam. We explained the evolution of the transmitted intensity and evaluated the start time of formation of the ripple structure. The induced permanent structure in the irradiated zones and the laser-induced surface morphology was studied using a polarising optical microscope and an atomic force microscope, respectively. The surface morphology in the irradiated zones was also dependent on both the power and polarisation of the Ar þ laser beam. The orientation of the microgrooves in the ripple structure was parallel to the polarisation direction of the pump laser beam in both configurations. For a given pump power, the depth of the ripple structure was greater in the case of an Ar þ beam polarised parallel to the easy axis. The induced azimuthal anchoring energy provided by the ripple structure was evaluated.

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