Biomedical subjects

Sonia Grego

Publications and source records attributed to Sonia Grego.

4 recordsLinked to original sources

PubMed2005

An AC electrokinetic technique for collection and concentration of particles and cells on patterned electrodes.

We report an electrohydrodynamic effect arising from the application of alternating electric fields to patterned electrode surfaces. The AC fields were applied to dilute suspensions of latex microspheres enclosed between a patterned silicon wafer and an ITO-coated glass slide in a small chamber. The latex particles became collected in the center of the conductive "corrals" on the silicon wafer acting as bottom electrode. The particle collection efficiency and speed depended only on the frequency and strength of the field and were independent of the material properties of the particles or the electrodes. The leading effect in the particle collection process is AC electrohydrodynamics. We discuss how the electrohydrodynamic flows emerge from the spatially nonuniform field and interpret the experimental results by means of electrostatic and hydrodynamic simulations. The technique allows three-dimensional microfluidic pumping and transport by the use of two-dimensional patterns. We demonstrate on-chip collection of latex particles, yeast cells, and microbes.

Journal Article↗

PubMed2005

Template-directed assembly on an ordered microsphere array.

We investigated the capability of an ordered array of microspheres to act as a template for deposition and ordering of a subsequent layer of microspheres. An evaporation-based technique was used to deposit monolayers of large colloidal spheres. A novel technique for selective deposition of polyelectrolyte film was used to stabilize the arrays and optimize the bead-substrate interaction. The template behavior of face-centered cubic and body-centered cubic (bcc) microsphere arrays was studied by optical and scanning electron microscopy, and the packing geometry was found to have a dramatic effect on the arrangement of the subsequent layer. A geometrical interpretation of the experimental data explains why a bcc bead array is well suited to act as a template for an additional layer of microspheres.

Journal Article↗

PubMed2002

The motion of a single molecule, the lambda-receptor, in the bacterial outer membrane.

Using optical tweezers and single particle tracking, we have revealed the motion of a single protein, the lambda-receptor, in the outer membrane of living Escherichia coli bacteria. We genetically modified the lambda-receptor placing a biotin on an extracellular site of the receptor in vivo. The efficiency of this in vivo biotinylation is very low, thus enabling the attachment of a streptavidin-coated bead binding specifically to a single biotinylated lambda-receptor. The bead was used as a handle for the optical tweezers and as a marker for the single particle tracking routine. We propose a model that allows extraction of the motion of the protein from measurements of the mobility of the bead-molecule complex; these results are equally applicable to analyze bead-protein complexes in other membrane systems. Within a domain of radius approximately 25 nm, the receptor diffuses with a diffusion constant of (1.5 +/- 1.0) x 10(-9) cm(2)/s and sits in a harmonic potential as if it were tethered by an elastic spring of spring constant of ~1.0 x 10(-2) pN/nm to the bacterial membrane. The purpose of the protein motion might be to facilitate transport of maltodextrins through the outer bacterial membrane.

Bacterial Outer Membrane Proteins↗

PubMed2002

EB1-microtubule interactions in Xenopus egg extracts: role of EB1 in microtubule stabilization and mechanisms of targeting to microtubules.

EB1 targets to polymerizing microtubule ends, where it is favorably positioned to regulate microtubule polymerization and confer molecular recognition of the microtubule end. In this study, we focus on two aspects of the EB1-microtubule interaction: regulation of microtubule dynamics by EB1 and the mechanism of EB1 association with microtubules. Immunodepletion of EB1 from cytostatic factor-arrested M-phase Xenopus egg extracts dramatically reduced microtubule length; this was complemented by readdition of EB1. By time-lapse microscopy, EB1 increased the frequency of microtubule rescues and decreased catastrophes, resulting in increased polymerization and decreased depolymerization and pausing. Imaging of EB1 fluorescence revealed a novel structure: filamentous extensions on microtubule plus ends that appeared during microtubule pauses; loss of these extensions correlated with the abrupt onset of polymerization. Fluorescent EB1 localized to comets at the polymerizing plus ends of microtubules in cytostatic factor extracts and uniformly along the lengths of microtubules in interphase extracts. The temporal decay of EB1 fluorescence from polymerizing microtubule plus ends predicted a dissociation half-life of seconds. Fluorescence recovery after photobleaching also revealed dissociation and rebinding of EB1 to the microtubule wall with a similar half-life. EB1 targeting to microtubules is thus described by a combination of higher affinity binding to polymerizing ends and lower affinity binding along the wall, with continuous dissociation. The latter is likely to be attenuated in interphase. The highly conserved effect of EB1 on microtubule dynamics suggests it belongs to a core set of regulatory factors conserved in higher organisms, and the complex pattern of EB1 targeting to microtubules could be exploited by the cell for coordinating microtubule behaviors.

Animals↗