Seminarios y Eventos

Seminars and Events

Nanoestructuras, Superficies, Recubrimientos y Astrofísica Molecular

Cordinador: Rául Gago


16 March 2017, 11:00 h. Salón de Actos

Organic field effect transistors in biosensing and neurosciences

Fabio Biscarini
Life Sciences Dept., Università di Modena e Reggio Emilia, Modena , Italy


Organic bioelectronics is an emerging platform with impact in diagnostics,
loco-regional treatments and theranostics. It is largely based on organic
field effect transistors (OFET) that can be operated as ultra-sensitive
biosensors, transducers of electrical and electrochemical signals from
cells, and stimulators for electroactive cells. Their applications range
from detection of biomarkers in bodily fluids to implants for bidirectional
communication with the central nervous system. Several OFET layouts have
been demonstrated to be effective in aqueous operations, which are
distinguished either by their architecture or by the respective mechanism
of doping by the ions in the electrolyte solution. In this work we discuss
first some fundamental aspects that concern the coupling mechanism of these
devices with the biological systems, in particular we elucidate the role of
the different interfaces into greatly enhancing the sensitivity of these
devices and their capability to amplify very small potential variations at
the interfaces. We also show that this device, operated as a biosensor for
a primary inflammatory citokine, i.e. TNF-alpha, responds
super-exponentially, and not linearly, in current vs analyte concentration
in the sub-nM range. We unify the super-exponential and linear regimes by
means of an alaysis of the density of states of the organic semiconductor
channel upon the change of the electro-chemical potential caused by the
adsorption of TNF-alpha. We finally show that the response is modulated by
the gate voltage applied, and that is possible to measure the association
binding constant of the antibody-antigen recognition, the molar free
energy, and the electrostatic contribution to the


21 February 2017, 15:00 h. Sala de Seminarios, 182

Atomic Force Microscopy in controlled environment: a powerful tool for original experiments on hybrid systems, biomaterials, and biocomposites

David Siniscalco
Université Bretagne Sud, CNRS Centre de Recherche C. Huygens


There is a growing research interest on hybrid systems, biomaterials, and biocomposites because of their industrial application demands. Owing unique properties of these materials make more attractive in electronic, medical and transport applications.
Whatever the application field, a constant need of miniaturization, performance, structure lightening necessitates working and exploring the material properties at nanoscale. To do this, one of the most powerful tool is Atomic Force Microscopy (AFM). By using AFM nanoscale tips, which interact with matter due to attractive and repulsive forces, numerous properties can be studied systematically. Due to its strong impact on properties and behaviour, temperature is considered as a key parameter. Indeed, its variations induce a significant change in material behaviour which can be positive (adhesion for example) or negative (electrical change). Consists of tip, micro-lever, photodetector, laser and control loop, the AFM can be used in different modes i.e. tapping, contact, non-contact, and PeakForce QNM. Consequently, a wide selection of measurements can be made under controlled environment (humidity, liquids, temperature, etc.,), and with different purposes such as topography, electrical measurements, force measurements, PeakForce-QNM.

To illustrate the contribution of the technics, different applications are presented. In the first part, a combination of AFM and RX reflectivity is used to understand the structure and interfaces of hybrid nanofilms (Polystyren/Gold) at different temperatures (-20°C to 220°C). In this way, AFM has been used to highlight different properties which are not possible to study by other technics such as electrical behaviour, adhesion and surface characterization with a new method


23 January 2017, 12:00 h. Salón de Actos

Semiconductor nanowire photonics

Carsten Ronning
Friedrich-Schiller-University of Jena, Germany


The miniaturization of light sources, the confinement and manipulation of light on a sub-wavelength scale as well as the detection of single photons are key challenges for the realization of future photonic circuits. Here, semiconductor nanowires are of major interest as a serving material platform, since they do not only offer superior photonic properties, but can also bridge the interface to electronic circuits enabled by their semiconducting properties. The efficient and sub-wavelength waveguiding of light is one of such superior photonic properties specifying nanowires as truly one-dimensional systems for photons. It is also an important prerequisite and defines the geometrical diameter limit for enabling lasing oscillations within nanowire cavities. High pumping powers and gain values are necessary in order to overcome the thresholds for amplified spontaneous emission (ASE) and laser oscillations. We determined those thresholds for both ZnO and CdS nanowires as well as the geometrical limitations. Furthermore, the laser output originating out of the end facet of a single nanowire was detected “head-on”, and a double pump technique was applied to measure the laser dynamics. Finally, I will present in this seminar a route for “optical doping” of such nanowires, which provides a useful benchmark for the future development of these nanoscale devices, as well as the possibility of coupling with plasmonic structures.


       

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