MipTec - The 9th International Conference and Exhibition on Drug Discovery
08.05.2006 - 11.05.2006

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Home - 09.05.2006 - Poster Session I

Poster Session I

Dienstag, 09. Mai 2006, 12:30 - 14:00

Winner of the Basel Award for best poster 2006:
The Use of Ultrasound to Create Two Dimensional Arrays for Drug Screening and Bioassays Applications

Stefano Oberti*, Adrian Neild, Jürg Dual ETH Zurich (Zurich, CH)

Newly synthesized drugs can be screened in a parallel fashion against living cells held at multiple distinct locations. Similarly, bioaffinity assays can be performed using polymeric beads coated with proteins or antibodies. If each row contains cells or beads of different type and each column is treated with a different flow, data from a two dimensional array can be obtained.
An ultrasonic field can be used to trap cells and beads (collectively termed particles) in such a two dimensional pattern. A particle in a sound field experiences a force which causes particles denser and stiffer than the host medium to gather in locations of vanishing pressure and particles less denser and less stiffer than the medium to be trapped at the pressure maxima.
In contrast to other techniques based on electrical, magnetic or optical principles, the acoustic field acts throughout the whole fluid volume and its periodicity (the wavelength is typically larger than the size of the particle) can be exploited to simultaneously position many particles, hence dispensing with the need of multiple transducers or actuation sites, as in the case for other techniques. This results in a simpler design. Furthermore, sample preparation is unnecessary.
A standing ultrasonic field can be created within a micromachined cavity containing the particle suspension etched in a silicon wafer by defining a strip electrode on the surface of a piezoelectric transducer attached beneath this cavity (Fig. 1). To provide optical access, the cavity is sealed with a glass plate. Two inlets at the sides are used to load the device through capillary effect. When the system is excited at those frequencies for which a resonance in the fluid occurs, a one dimensional pressure field is then created, which causes particles to collect into lines parallel to the strip electrode.
We present here an extension of the previous principle, whereby superimposing the one dimensional fields created by a set of orthogonally oriented electrodes on the piezoelectric surface a two dimensional ultrasonic field capable of collecting particles at circular points is created. Depending on the number of active electrodes one can therefore decide whether to collect particles in lines or at points.
The working principle is illustrated using copolymer beads of 26 microns diameter first collected in lines and then separated into circular clumps (Fig. 2) and MCF10A cells positioned into clumps starting from a random distribution (Fig. 3).