60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007;
Salt Lake City, Utah
Session LT: Invited Session: Making shock waves in microfluidics: The physics and applications of isotachophoresis
10:30 AM–11:05 AM,
Tuesday, November 20, 2007
Salt Palace Convention Center
Room: Ballroom FH
Chair: Haim Bau, University of Pennsylvania
Abstract ID: BAPS.2007.DFD.LT.1
Abstract: LT.00001 : Making Shock Waves in Microfluidics: The Physics and Applications of Isotachophoresis
10:30 AM–11:05 AM
Preview Abstract
Author:
Juan Santiago
(Stanford University)
Microfluidics lies at the interfaces between engineering, chemistry, and
biology, and aims to develop chemical laboratories on a chip. An important
technique is on-chip capillary electrophoresis which has been applied to a
wide range of chemical and biochemical assay applications over the last
decade. Perhaps the best way of improving the sensitivity of on-chip
electrophoresis is to integrate an online sample preconcentration method.
At Stanford, we are developing methods to concentrate ions into small
volumes using a method called isotachophoresis (ITP). In ITP, sample ions
are injected between the high mobility co-ions of a leading electrolyte (LE)
and the low mobility co-ions of a trailing electrolyte (TE). Upon
application of an electric field, the disparate ion mobilities of the LE and
TE cause sample species to segregate and focus into a series of narrow
self-sharpening zones which migrate at equal velocity (hence ``isotacho'').
ITP-type processes have been studied and used for more than 60 years, and
yet there remain significant challenges in the robust modeling of these
transport processes and the creation of widely applicable assays. We use ITP
to create sample ion concentration ``shock waves'' in microchannels. These
concentration waves can be integrated with on-chip electrophoresis for high
sensitivity assays, and novel modes of operation. The talk will summarize
the basic physics of ITP, experimental studies of ITP, models of ITP, and
the development of novel ITP-assays with unprecedented sensitivity and new
functionality. For example, using leading-to-sample ion concentration ratios
of 10$^{15}$ and local electric fields of $\sim $4~kV/cm, we can achieve
order one micron wide ITP zones. We can achieve million fold
preconcentration in 120~s and can detect 100~attomolar sample concentrations
(to our knowledge the highest demonstrated sensitivity for an
electrophoresis-related assay). We have also developed a method that uses
ITP to separate, indirectly detect, and identify the electrophoretic
mobilities of unlabeled (non-fluorescent) analytes using surrogate
fluorescent molecules. Our goal is the development of novel on-chip ITP
assays which expand the design space of microfluidic devices.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.DFD.LT.1