<title>Silicon microphysiometer for high-throughput drug screening</title>

Abstract

ABSTRACT We report on a micromachined silicon chip that is capable of providing a high-throughput functional assay based oncalorimetry. A prototype twin microcalorimeter based on the Seebeck effect has been fabricated by IC technology andmicromachined postprocessing techniques. A biocompatible liquid rubber membrane supports two identical O.5x2 cm2measurement chambers, situated at the cold and hot junction of a 666-junction aluminum/p+-polysilicon thermopile. Thechambers can house up to 106 eukaryotic cells cultured to confluence. The advantage ofthe device over microcalorimeters onthe market, is the integration ofthe measurement channels on chip, rendering microvolume reaction vessels, ranging from 10 to 600 tl, in the closest possible contact with the thermopile sensor (no springs are needed). Power and temperature sensitivity of the sensor are 23 V/W and 130 mVIK, respectively. The small thermal inertia of the microchannels results inthe short response time of 70 s, when filled with 50 il of water.Biological experiments were done with cultured kidney cells ofXenopus laevis (A6). The thermal equilibration time of thedevice is 45 mm. Stimulation of transport mechanisms by reducing bath osmolality by 50% increased metabolism by 20 %.Our results show that it is feasible to apply this large-area, small-volume whole-cell biosensor for drug discovery, where thebinding assays that are commonly used to provide high-throughput need to be complemented with a functional assay.Solutions are brought onto the sensor by a simple pipette, making the use of an industrial microtiterplate dispenser feasibleon a nx96-array of the microcalorimeter biosensor. Such an array of biosensors has been designed based on a new set cfrequirements as set forth by people in the field as this project moved on. The results obtained from the prototype large-areasensor were used to obtain an accurate model ofthe calorimeter, checked for by the simulation software ANSYS. At present,the sensor chip has been designed. Future publication(s) will deal will this part ofthe work.Key words: whole cell biosensor, physiometer, thermopile, sensor array, micromachining, high-throughput drug screening,cell metabolism, functional assay, microtiterplate