Dielectrophoresis (DEP) is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. DEP can be used to manipulate, transport, separate and sort different types of particles. There are a lot of opportunities to exploit this method in the field of bio-related microfluidics, since biological cells already have dielectric properties.

The growing interest in DEP was evident at the recent 2009 Conference on Advances in Microfluidics and Nanofluidics in Hong Kong (Jan. 5-7). In fact, the editor of Biomicrofluidics was ecstatic, commenting, "We are in DEP heaven!"

A noteworthy work by Daniel Ou-Yang's group at the Physics department of Lehigh measures the DEP mobility of nanocolloids with an optical tweezers technique, as seen in his invited article in BMF¹. Note that he measures not just the cross-over but the mobility as a function of frequency. You will note in his last two figures the anomalous scalings that defy the Clausius-Mossotti theory.

Other notables right now include Elaine Zhu and Jiang Zhao who are working on molecular DEP—AC induced dipolar effects on polyelectrolyte conformation and hybridization with fluorescence correlation spectroscopy (FCS) techniques. Elaine just published a paper with Peter Hoffmann and Prasad Sarangapani in Langmuir² on binary nanocolloid phase separation by DEP and with Victoria Froude in an upcoming J. Phys. Chem. paper on DEP of liposomes. There are beautiful images and a very good characterization of surface conductance effect in Victoria's paper!

Another notable DEP paper is one on how DNA hybridization of nanocolloids changes their cross-over, by Zachary Gagnon and Senapati³, and was fast-tracked and featured on the cover of the December issue of Electrophoresis.

¹Ming-Tzo Wei, Joseph Junio, H. Daniel Ou-Yang (2009). Direct measurements of the frequency-dependent dielectrophoresis force Biomicrofluidics, 3 (1), DOI: 10.1063/1.3058569

²Peter D. Hoffman, Prasad S. Sarangapani, Yingxi Zhu (2009). Dielectrophoresis and AC-Induced Assembly in Binary Colloidal Suspensions Langmuir, 24 (21), DOI: 10.1021/la8013392

³Zachary Gagnon, Satyajyoti Senapati, Jason Gordon, Hsueh-Chia Chang. Dielectrophoretic detection and quantification of hybridized DNA molecules on nano-genetic particles Electrophoresis, 29 (24), DOI: 10.1002/elps.200800528

Greetings from Hong Kong!

A sunny day here at the Hong Kong University of Science and Technology marks the start of this first conference on Advances in Microfluidics and Nanofluidics.

Registration has been busy and the theater was full when Professor Weijia Wen, HKUST, welcomed the audience and Professor Hsueh-Chia Chang, Notre Dame, gave the opening remarks. With a full agenda of excellent speakers and a hall full of posters it seems we are set for a very nice start to the conference.

As the affiliated journal, Biomicrofluidics, is being represented via a stand just outside the entrance to the lecture theater. With lunch being served in the area directly in front of our stand, we hope to be able to interact with most of the researchers in attendance.