This paper presents a case study, carried out as a senior product design project (Chen et al., 2005), for the design of a chip for screening kinase inhibitors (KIs), which are promising cancer therapeutics. A poly(dimethyl-siloxane), PDMS chip is created using soft lithography. Using Fluidigm technology (Quake et al., 2000), devices for control (valves and peristaltic pumps) are added to the chip in a so-called multilayer soft lithography process. The top layer involves pressure-driven channels, which run orthogonal to the lower channels, controlling the fluid flow in the lower channels. The latter contain the reagents for all of the assays to be carried out.

Emphasis is placed on strategies for the design of this configured consumer product, which is manufactured for use by pharmaceutical companies that have the need to perform standardized kinase inhibition assays on potential new KIs. In the case study, the chips are designed to carry out about 10,000 assays per day, with each assay requiring on the order of 10-100 nl total reaction volume per assay. Luminescence is used to report the concentration of adenosine triphosphate (ATP), which is bound to an active site on a target protein by a kinase enzyme. The KIs are designed to compete with the target protein by binding to the kinase enzyme's active site.

Using microfluidic pumping and mixing, an array of reacting droplets (boluses) containing a range of concentrations for each of several KIs is created on the chip. The reacting boluses for each inhibitor provide sufficient information to generate an IC50 curve; that is, a curve that identifies the concentration of KI at which the rate of the binding reaction is reduced by 50 percent. Key design variables involve the spacing of the 50 and 100 µm channels on a 1”×1” chip, the number of boluses per IC50 curve, and the reaction time.

Chen, Q.-M., L. B. Heend, and J. Waring, NANOLUX Screening Technologies, Towne Library, Univ. of Pennsylvania, 2005.

Quake, S. R., H. P. Chou, M. A. Unger, T. Thorsen, and A. Scherer, “Monolithic Microfabricated Valves and Pumps by Multilayer Soft Lithography,” Science, 388, 113-116 (2000).