Figure 1 The Aurora Ultra-High-Throughput Screening System (UHTSS). The compounds are stored in industry-standard 96- and 384-well storage plates in the store. Compounds are screened for effects on physiological processes (probed in the assay cell lines) by automated selection from the store and conveyance of the compound plate to replication stations, where compounds are prepared for assay. Assays are staged by combining the compounds with assay reagents and cells in miniaturized reaction vessels at the microfluidic stations, incubating the reagents, and measuring fluorescence of donor and acceptor fluorophores at the detector.

To facilitate construction of parallel assays for large numbers of test compounds at a time, special high-density reaction well formats have been created that enable scaling of biological assays to the reduced volume required. To construct assays in small volumes requires confluence of accurate and precise fluid handling, automated positioning of fluid dispensers, and assay well design to avoid a series of potential pitfalls inherent in miniaturization. Thus, assays are constructed by bringing reaction wells that are formatted to evolving industry-standard designs under arrays of multiplexed fluid dispensers from which are ejected the constituents of the reaction. These include the engineered cells developed to serve as chemical and physiological platforms for the reaction, the cell culture medium, the buffers and any particular reagent requirements, the cell-permeant dual fluorophore, the traditional agonist (or antagonist) used to stimulate the transduction pathway, and the chemical compound under test. Each reaction requires

a particular concentration of reagent or compound, and the delivery of each chemical may be constrained by particular physical properties such as solubility. Thus, loading an assay to a total final volume of 1-2 µl requires combining assay constituents that are dispensed in volumes that may range from 0.1 to 1 µl (i.e., a range of 10,000-fold). This range of volumetric liquid delivery requires dispenser modalities that are adapted and suitable for specific ranges of volumes such as 0.1-10 µl or 0.1-10 nl. Each range of dispensing is performed by a single modular platform that can be replicated for the different reagents or to improve speed of delivery. Typically at these volume ranges, noncontact dispensation methods have inherent advantages over contact-based methodologies. Contact-based dispensation can be particularly effective in a “touch-off” mode with larger volumes or in dry plates but becomes cumbersome in small volumes.