Dielectrophoretic spectra of translational velocity and critical frequency for a spheroid in traveling electric field.

An analysis has been made of the dielectrophoretic (DEP) forces acting on a spheroidal particle in a traveling alternating electric field. The traveling field can be generated by application of alternating current signals to an octapair electrode array arranged in phase quadrature sequence. The frequency dependent force can be resolved into two orthogonal forces that are determined by the real and the imaginary parts of the Clausius-Mossotti factor. The former is determined by the gradient in the electric field and directs the particle either toward or away from the tip of the electrodes in the electrode array. The force determined by the imaginary component is in a direction along the track of the octapair interdigitated electrode array. The DEP forces are related to the dielectric properties of the particle. Experiments were conducted to determine the DEP forces in such an electrode arrangement using yeast cells (Saccharomyces cervisiate TISTR 5088) with media of various conductivities. Experimental data are presented for both viable and nonviable cells. The dielectric properties so obtained were similar to those previously reported in literature using other DEP techniques.

Biographical memoir: Alexander Beaumont Hope, Australian biophysicist, 1928-2008.

This introductory article is the first of four short articles from the Tribute to Alex Hope Symposium held at the 2008 Australian Society for Biophysics meeting in Canberra, Australia, as a tribute to Professor Alex Hope, who died in July last year. As well as briefly introducing the other three articles by three former PhD students, it will also be a biographical memoir of Alex Hope.

Structural characterization of organic multilayers on silicon(111) formed by immobilization of molecular films on functionalized Si-C linked monolayers.

Silicon(111)-H surfaces were derivatized with omega-functionalized alkenes in UV-mediated and thermal hydrosilylation reactions to give Si-C linked monolayers. Additional molecular layers of organic compounds were coupled either directly or via linker molecules to the functionalized alkyl monolayers. In the first instance, amino-terminated monolayers were prepared from a tert-butoxycarbonyl-protected omega-aminoalkene followed by removal of the protecting group. Various thiols were coupled to the monolayer using a heterobifunctional linker, which introduced maleimide groups onto the surface. In the second system, N-hydroxysuccinimide (NHS) ester-terminated monolayers were formed by reaction of Si-H with N-succinimidyl undecenoate. The reactivity of the NHS ester groups was confirmed by further modification of the monolayer. The stepwise assembly of these multilayer structures was characterized by X-ray reflectometry and X-ray photoelectron spectroscopy.

Electrical breakdown of human erythrocytes: a technique for the study of electro-haemolysis.

This paper describes a technique suitable for investigating the electromechanical breakdown properties of erythrocyte cells. The cells were exposed to square wave electric pulses of precise duration and voltage. The erythrocytes were suspended in normal isotonic saline between two opposing platinum electrodes. A red LED light source and photodiode detector system were positioned orthogonally to the electrodes to record changes in the light transmission that occur immediately after applying an electric pulse. The light transmitted through the electrically treated erythrocyte suspension could be monitored continuously. Experiments were conducted to explore the inter-relationship between the critical voltage and pulse length for haemolysis. Human blood taken from "healthy" donors underwent haemolysis at a critical field strength of 304 kV/m for a 5 micros pulse and 292 kV/m for a 50 micros pulse. The relationship of critical pulse length and critical voltage for the blood samples was found to be inversely linear.

Electric field effects in proteins in membranes.

Both the organization and function of protein nanostructures in membranes are related to the substructural properties of the lipid portion of the membrane. Potential differences that are established across the membrane and generate electric fields in these very thin portions are shown to modulate the organizational and functional properties of the protein modules. Many protein modules also have nonisotropic distributions of charged sites, including configurations in which there are regions containing predominantly positive fixed charges, juxtaposed with adjacent regions containing predominantly negative fixed charges. In these double fixed charge regions, very large electric fields can manifest in the ionic depletion layer at the junction of the two fixed charge regions. Consideration is also given to the manner in which the intense electric fields that are established in protein modules, such as proton ATPases, can modulate the chemical reactions that are associated with proton transport and dehydration reactions.