Impedance measurements of cell suspensions represent a well-established technique for determining the density of cells and their electrical properties. It only deserves a parallel plate capacitor or a comparable arrangement between which the cell ensemble has to be suspended. In order to avoid galvanic currents to occur between the electrodes, generally, alternating currents in the kHz- up to the MHz-range are applied for this purpose.
The availability of high-frequency impedance sensors by virtue of IHP’s SiGe:C heterobipolar transistors offers the opportunity to design impedance circuits that operate in the GHz range. Appropriate sensor chips have been prepared in the pilot line of IHP’s CMOS/BiCMOS clean room, and the figure shows an example. Their test in biotech environments is performed by integrating them into microtiter plate-sized platforms, so that their operation can be verified on vibrators, pipetting robotic systems and other realistic conditions.