Microsystem technology (MST) is currently making a dramatic progress within the field of life science. A driving factor for this is the tremendous need of technology advancements in bioanalytical techniques to meet the expected demands as we are now entering the post genomic era and face much more complex biological queries than in the process of decoding the human genome. One of the most targeted areas are the efforts to find new technologies to perform protein analysis commonly called protein chips.

Microbeads are by several groups considered to be a fundamantal base for this development due to its inherently large surface area and thereby high analytical sensitivity. To be able to use these particles to dynamically generate protein arrays a microfluidic system making it possible to trap and manipulate the particles is needed. A microfluidic system based on particles will result in smaller sample volumes, higher throughput and a more flexible analytical system.

A microfluidic device using ultrasonic forces to trap and manipulate microparticles has been developed and verified. The device uses an array of miniaturised ultrasonic transducers integrated in the walls of a microchannel. The transducers are designed to work as acoustic resonators creating standing ultrasonic waves in the channel. Microparticles are forced to the pressure nodes or anti-nodes created in the nearfield of the transducer and are trapped by the ultrasonic forces.

Three sub-millimetre transducer elements were mounted on a printed circuit board (PCB) which was cast with epoxy. The epoxy was hardened and polished down to the upper surface of the transducer elements. To provide inlets and outlets for the fluid, holes were drilled in the PCB. Microchannels were fabricated using a photosensitive polymer, SU-8, on soda-lime glass substrates. The channels were 1 mm wide and less than 100 µm deep. The glass substrate was clamped onto the PCB to seal the channel against the epoxy surface. The whole unit was designed to work as a resonator to create a pressure node in the middle of the channel at 10 Mhz.

The device was evaluated using 5 µm polyamide particles suspended in water. The particles were trapped in the middle of the channel and held at a fluid flow of up to 1 mm/s. By switching off the ultrasound all microparticles were released.

In future work methods to expand the system to a two-dimensional array will be investigated together with possibilities to perform biochemical analysis.
Notes: Poster