The 404pi is a surface plasmon resonance (SPR) instrument that incorporates phase-based common path interferometry technology. The 404pi features technology that allows for the simultaneous monitoring of multiple analytes in a single sample. This class of SPR instrumentation has been designed to measure protein/protein and protein-small molecule interactions (down to 100 Da) in a high-throughput 96/384-well platform utilizing four parallel channels rather than a single flow cell.