Thermally-modulated shape transition at the interface of soft gel filament and hydrophobic substrate.

A liquid filament may pinch off into different shapes on interacting with a soft surface, as modulated by the interplay of inertial, capillary, and viscous forces. While similar shape transitions may intuitively be realized for more complex materials such as soft gel filaments as well, their intricate controllability towards deriving precise and stable morphological features remains challenging, as attributed to the complexities stemming from the underlying interfacial interactions over the relevant length and time scales during the sol-gel transition process. Circumventing these deficits in the reported literature, here we report a new means of precisely-controlled fabrication of gel microbeads via exploiting thermally-modulated instabilities of a soft filament atop a hydrophobic substrate. Our experiments reveal that abrupt morphological transitions of the gel material set in at a threshold temperature, resulting in spontaneous capillary thinning and filament breakup. We show that this phenomenon may be precisely modulated by an alteration in the hydration state of the gel material that may be preferentially dictated by its intrinsic glycerol content. Our results demonstrate that the consequent morphological transitions give rise to topologically-selective microbeads as an exclusive signature of the interfacial interactions of the gel material with the deformable hydrophobic interface underneath. Thus, intricate control may be imposed on the spatio-temporal evolution of the deforming gel, facilitating the inception of highly ordered structures of specific shapes and dimensionalities on demand. This is likely to advance the strategies of long shelf-life analytical biomaterial encapsulations via realizing one-step physical immobilization of bio-analytes on the bead surfaces as a new route to controlled materials processing, without demanding any resourced microfabrication facility or delicate consumable materials.

Kinetics of protein aggregation at a temperature gradient condition.

The unconventional multi-sigmoidal kinetic behaviour of protein aggregation at a temperature gradient condition is reported in this study. To establish a feasible theory for protein aggregation kinetics at a temperature gradient condition, the spatial height of the protein solution is divided into hypothetical layers and the kinetic equations in those layers are solved. Furthermore, we endeavour to study numerically the effect of the temperature gradient on the kinetics of oligomer-mediated protein aggregation and protein inhibition.

Fibril growth captured by electrical properties of amyloid-ß and human islet amyloid polypeptide.

The aggregation of amyloid-ß (Aß) and human islet amyloid polypeptide (hIAPP) proteins have attracted considerable attention because of their involvement in protein misfolding diseases. These proteins have mostly been investigated using atomic force microscopy, transmission electron microscopy, and fluorescence microscopy to study the directional growth of fibrils both perpendicular to and along the fibril axis. Here, we demonstrate the real-time monitoring of the directional growth of fibrils in terms of activation energy of proton transfer using an impedance spectroscopy technique. The activation energy is used to quantify the sensitivity of proton conduction to the different stages of protein aggregation. The decrement (increment) in activation energy is related to the fibril growth along (perpendicular to) the fibril axis in intrinsic protein aggregation. The entire aggregation process shows different phases of the directional growth for Aß and hIAPP, indicating different pathways for their aggregation. The activation energy for hIAPP is found to be smaller than the activation energy of Aß during the aggregation process. The oscillatory behavior of the activation energy of hIAPP reflects a rapid change in the directional growth of the protofilaments of hIAPP. The results indicate higher aggregation propensity of Aß than hIAPP. In the presence of resveratrol, hIAPP exhibits slower aggregation compared to Aß. Methods of this study may in general be used to reveal the modulated aggregation pathway of proteins in the presence of different ligands.

Reduced electrode polarization at electrode and analyte interface in impedance spectroscopy using carbon paste and paper.

The double layer present at the interface of an electrode and an analyte causes electrode polarization (EP) in impedance spectroscopy, which hinders acquiring the actual impedance of biological samples at a lower frequency region. In this work, a novel carbon paste (CP) electrode material prepared by mixing the pencil graphite powder with transparent glue has been reported to reduce the EP by depositing its two coplanar electrodes on a chromatography paper substrate. Furthermore, two other devices having silver paste and pencil electrodes on the chromatography paper have been fabricated, analyzed for the EP, and compared with the CP electrode. The EP is quantified by fitting the impedance data to an equivalent electrical circuit having double layer capacitance as a constant phase element, and the CP electrode shows the lowest EP among the electrodes. The cyclic voltammetry analysis reveals blocking electrode property of the CP, which diminishes dc current flow at the electrode/electrolyte interface. Furthermore, the chromatography paper is found to increase the effective surface area of the deposited electrode by enhancing its surface roughness, which helps reduce the EP.