13 research outputs found
Phoretic Motion of Spheroidal Particles Due To Self-Generated Solute Gradients
We study theoretically the phoretic motion of a spheroidal particle, which
generates solute gradients in the surrounding unbounded solvent via chemical
reactions active on its surface in a cap-like region centered at one of the
poles of the particle. We derive, within the constraints of the mapping to
classical diffusio-phoresis, an analytical expression for the phoretic velocity
of such an object. This allows us to analyze in detail the dependence of the
velocity on the aspect ratio of the polar and the equatorial diameters of the
particle and on the fraction of the particle surface contributing to the
chemical reaction. The particular cases of a sphere and of an approximation for
a needle-like particle, which are the most common shapes employed in
experimental realizations of such self-propelled objects, are obtained from the
general solution in the limits that the aspect ratio approaches one or becomes
very large, respectively.Comment: 18 pages, 5 figures, to appear in European Physical Journal
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
ELECTRON TRANSPORT IN METAL-INSULATOR- METAL JUNCTION BASED ON SELF -ASSEMBLED MONOLAYERS
trasferimeto elettronico in giunzioni molecolari che incorporano molecole organiche di diversa struttura elettronic
CORRELATING ELECTRON TRANSPORT AND CHEMICAL STRUCTURE
correlazione fra struttura elettronica, interazioni molecolari e velocità di trasferimento eletttronic
Patterned delivery and expression of gene constructs into zebrafish embryos using microfabricated interfaces
We demonstrate a method which uses simple microfabrication and microfluidics to produce custom, shaped electroporators for the patterned delivery of foreign molecules into developing embryos. We show how these electroporators can be used to 'draw' two-dimensional patterns of tracer molecules, DNA and mRNA into the yolk and cells of zebrafish embryos (Danio rerio) at different stages of development. We demonstrate the successful delivery of patterns of Trypan Blue (normal dye), Texas Red (fluorescent dye), GFP-expressing DNA plasmids and GFP expressing mRNA constructs into both chorionated and dechorionated embryos. Both DNA and mRNA were expressed in the desired patterns subsequent to delivery. Square pulses of 10-20 V (0.20-0.40 kV/cm), 50-100 ms width were sufficient to create transient pores and introduce compounds from the late blastula period (3 hpf) to early pharyngula period (24 hpf) embryos. Using 24 hpf dechorionated embryos, we achieved a high survival of 91.3% and 89%, and a delivery efficiency of 38% and 50% for GFP-DNA and GFP-mRNA respectively. Lastly, we demonstrate the simultaneous delivery of different compounds into the developing embryo.close8
Generating steep, shear-free gradients of small molecules for cell culture
We present the fabrication, characterization and cell culture results of a microfluidic device for generating steep gradient interfaces of small molecules (< 1 kDa) across cell culture with no convective shear stresses applied to the cells. We use a novel streamline of two fluids to generate stable and uniform gradient interfaces/boundaries by confronting one fluid with the other. We separate a gradient generation channel and a cell culture channel by a polyester membrane so that viscous shear stress by the bottom channel flow does not convectively disturb the chemical environment of cultured cells seeded on the membrane in the top channel. Using two-component dyes to characterize the steepness of the diffusional interface, we demonstrate 50 mu m wide steps for about 400 Da molecules. Using BCECF, a 689 Da pH-sensitive diffusible dye which is actively taken up by living cells, we demonstrate gradient boundaries narrower than five cell diameters in HeLa culture. We also demonstrate steep gradients of pH across cells in the same device. This work should be of interest to researchers attempting to generate gradients of small, rapidly diffusing molecules for studies in cellular differentiation and signaling.close32