3 research outputs found
Switchable Hydrogel-Gated Organic Field-Effect Transistors
Stimuli-responsive
hydrogels represent a class of materials capable
of reversibly switching their morphological and physicochemical characteristics.
An ultrathin poly(acrylic acid) film (ca. 6 nm) grafted onto the gate
of a p-type EGOFET is studied, and the correlation between the swelling
state of the hydrogel and the transistor output characteristics is
presented. The hydrogel-related swelling process occurring in basic
medium causes an increase in threshold voltage due to the abrupt and
intense increase of the negative charge density on the gate electrode.
The variation of the drain current during the <i>in situ</i> modification of the pH electrolyte allows a quantitative analysis
of the hydrogel switching kinetics. This work shows not only the relevance
of EGOFET as an analytical tool in the broad sense, i.e., able to
follow in real time phase transition processes of stimuli-responsive
materials, but also the relevance of using a hydrogel for field-effect-based
(bio)detection according to the ability of such material to overcome
the well-known Debye length problematics
Molecular Dynamics Simulation of a RNA Aptasensor
Single-stranded RNA
aptamers have emerged as novel biosensor tools.
However, the immobilization procedure of the aptamer onto a surface
generally induces a loss of affinity. To understand this molecular
process, we conducted a complete simulation study for the Flavin mononucleotide
aptamer for which experimental data are available. Several molecular
dynamics simulations (MD) of the Flavin in complex with its RNA aptamer
were conducted in solution, linked with six thymidines (T6) and, finally,
immobilized on an hexanol-thiol-functionalized gold surface. First,
we demonstrated that our MD computations were able to reproduce the
experimental solution structure and to provide a meaningful estimation
of the Flavin free energy of binding. We also demonstrated that the
T6 linkage, by itself, does not generate a perturbation of the Flavin
recognition process. From the simulation of the complete biosensor
system, we observed that the aptamer stays oriented parallel to the
surface at a distance around 36 Å avoiding, this way, interaction
with the surface. We evidenced a structural reorganization of the
Flavin aptamer binding mode related to the loss of affinity and induced
by an anisotropic distribution of sodium cationic densities. This
means that ionic diffusion is different between the surface and the
aptamer than above this last one. We suggest that these findings might
be extrapolated to other nucleic acids systems for the future design
of biosensors with higher efficiency and selectivity
Insights into Structural Behaviors of Thiolated and Aminated Reduced Graphene Oxide Supports to Understand Their Effect on MOR Efficiency
It is essential to develop novel
catalysts with high catalytic
activity, strong durability, and good stability for further application
in methanol fuel cells. In this work, we present for the first time
the effect of the chemical functional groups (thiol and amine) with
different electron affinity in reduced graphene oxide supports on
the morphology and catalytic activity of platinum nanoparticles for
the methanol oxidation reaction. Hydroxyl groups on graphene oxide
were initially brominated and then transformed to the desired functional
groups. The good dispersion of metal nanoparticles over functionalized
carbon substrates (particle size less than 5 nm) with good durability,
even at a limited functionalization degree (less than 7%) has been
demonstrated by morphological and structural studies. The durability
of the catalysts was much improved via strong coordination between
the metal and nitrogen or sulfur atoms. Impressively, the catalytic
activity of platinum nanoparticles on aminated reduced graphene oxide
was found to be much better than that on thiolated graphene oxide
despite the weaker affinity between amine and noble metals. These
findings support further developing new graphene derivatives with
the desired functionalization for electronics and energy applications.