Microfabricated Thermal Gradient Separator Device

The design and fabrication of a microfabricated fluidic device for particle thermophoresis is presented. The ability of the device to concentrate particles by generating a huge thermal gradient is demonstrated. In contrast to other microfluidics devices which use electrokinetics or pressure driven flow, in this device no external force acts on the particles. The separator device has been fabricated in a standard silicon substrate, consisting of a 20 μm deep channel and a 600 nm thick aluminum heater integrated into the device. The device is able to create a thermal gradient of approximately 10⁴ Km⁻¹. To maintain a thermal gradient over a long period, special attention had to be given to the design of the integrated heater and thermal insulation of the channel. In order to deposit the aluminum heater on the side wall of a micro channel, a silicon substrate was wet etched in KOH solution, forming sloping sidewalls. The temperature difference was measured using a thermocouple mounted on the two sides of the channel walls, showing about 2 K temperature difference. Experimental studies have been conducted in order to study the motion of particles in response to the thermal gradient. Particle motions are recorded before and after turning on the heater. Using polystyrene latex particles suspended in de-ionized water, it is shown that 90% of particles are concentrated on the cold side of the channel after 300 seconds using only 1W of electrical power. Apart from its applicability to particle suspensions, this device also has a great potential for DNA molecule concentration and separation in bio-chemical analysis.