Resonant waveguide grating (RWG) systems illuminate an array of diffractive nanograting waveguide structures in microtiter plate to establish evanescent wave for measuring tiny changes in local refractive index arising from the dynamic mass redistribution of living cells upon stimulation. Whole-plate RWG imager enables high-throughput profiling and screening of drugs. Microfluidics RWG imager not only manifests distinct receptor signaling waves, but also differentiates long-acting agonism and antagonism. Spatially resolved RWG imager allows for single cell analysis including receptor signaling heterogeneity and the invasion of cancer cells in a spheroidal structure through 3-dimensional extracellular matrix. High frequency RWG imager permits real-time detection of drug-induced cardiotoxicity. The wide coverage in target, pathway, assay, and cell phenotype has made RWG systems powerful tool in both basic research and early drug discovery process.
G protein-coupled receptors (GPCRs) are the largest family of cell surface proteins involved in transmitting extracellular signals to the interior of the cell. These membrane-spanning proteins constitute one of the most important families of drug targets. Despite their importance, the power and utility of microarray technology has not been extended to GPCRs or other membrane proteins because of issues due to immobilization - these proteins typically need to be embedded in membrane environment to maintain their native conformations. This paper describes the fabrication of GPCR microarrays by conventional robotic pin-printing and demonstrates straightforward assays for screening of ligands on these arrays. GPCRs, obtained as membrane preparations form cell lines over-expressing particular GPCRs, were arrayed using a quill-pin printer. The arrays were incubated with solutions of labeled cognate ligands and unlabeled compounds, and imaged using a fluorescence scanner. The assays conducted were designed to test: (i) the specificity of ligand binding among different families of GPCRs; (ii) the selectivity of ligand binding and inhibition among different members of a GPCR family; (iii) the affinity of ligand binding. The results showed highly selective binding of ligands to arrays of receptors, with affinities similar to those reported in the literature and obtained suing other techniques. This demonstration of membrane-protein arrays and associated assays overcomes a fundamental limitation in protein microchip technology - the lack of practical microarray based methods for membrane proteins.