Temperature gradient focusing in microfluidic channels. (General Developments).

NIST scientists have developed a new method to concentrate and separate chemical species in micro-fluidic channels. Microfluidic, or "lab-on-a-chip," devices are miniaturized chemical and biochemical analysis systems that one day may replace conventional bench top instruments.

The new technique, temperature gradient focusing, balances the electrophoretic motion of analytes in a microchannel against the bulk flow of buffer solution through the microchannel while applying both an electric field and a temperature gradient along the length of the channel. For buffer solutions having temperature-dependent ionic strength, the applied temperature gradient results in a corresponding gradient in the electrophoretic velocity of a charged analyte in the channel. The bulk flow velocity can then be adjusted so that the total analyte velocity (the sum of the bulk and electrophoretic velocities) is zero at some point along the channel length, and all of the analyte in the channel will be focused, or concentrated, at that point.

The technique gives simultaneous focusing and separation of differently charged analytes in a manner analogous to isoelectric focusing of proteins, but is much simpler to implement than isoelectric focusing and has the additional advantage of working with any charged analyte, rather than just proteins. Temperature gradient focusing has been demonstrated for a variety of different analytes including fluorescent dyes, amino acids, proteins, DNA, and colloidal particles. In addition, it has been shown to be capable of greater than 10 000-fold concentration of a dilute analyte. A description of the technique has been published in the journal Analytical Chemistry [(David Rosso and Laurie Locascio, Anal. Chem. 74(11), 2556-2564 (2002)].

CONTACT: David Ross, [phone]; [e-mail] or Laurie Locascio, [phone]; [e-mail].