Optical assay apparatus and methods are provided having an optical assay cup for detecting analytes in a sample fluid. The cup's sidewall may include an optical waveguide having a detection coating on its inner surface. During use, the waveguide receives evanescent or darkfield interrogation light, interrogates at least part of cup's interior volume with it, and emits signal light as a function of the analytes. The detection coating may have fluid or non-fluid detection layers, at least part of which may form at least part of a waveguide for the interrogation light. The cup may be spun during use, such as to centrifugally-concentrate any high-density analytes towards cup's sidewall. The assay apparatus may further include an interrogation light source, a cover or spinning apparatus for the cup, and an optical detector for the signal light.