The present invention provides disposable, semi-reusable, or single use reaction vessels with integrated optical elements for use with diffraction based assay systems. The vessel for assaying liquids for analytes includes a housing having at least one chamber or well for receiving a liquid therein and an optical element integrally formed with the housing for directing an incident light beam towards the well or chamber and directing a light beam away from the chamber after the light beam has interacted with analytes present in the liquid. The vessel may be test tube such as a blood collection tube, with or without, an optical element but having a pattern of analyte-specific receptors located on an inner surface of the tube wall so that when a liquid is introduced into the interior of the test tube analytes present in the liquid can bind with the pattern of analyte-specific receptors.