In a multiplexed assay, each molecule of a plurality of molecules is attached to a support matrix particle with a substrate adapted for attachment and/or synthesis of molecules. A spectrally-encoded identifier embodied in a photochemical medium is embedded or encased within the substrate to uniquely identify the molecule attached to the substrate. The molecules are exposed to one or more processing conditions, and then placed within the path of an optical detector adapted to read the spectrally-encoded identifier and measure biochemical activity on each support matrix particle. The measured biochemical activity is associated with the unique identity of the support matrix particle and, hence, with the molecule attached to the particle.