A test system includes an optical medium, a binding agent capable of capturing a target complex, and a light detector. The optical medium provides a light path, and the binding agent is positioned to hold the target complex in an evanescent field created by propagation of light along the light path. The complex interacts with the evanescent field and emits light that the detector positioned to detect. The optical medium and the detector can be included in an optical integrated circuit where detected light passes through the optical medium transverse to the direction of the light path.