A micro bead having a digitally coded structure that is partially transmissive and opaque to light. The pattern of transmitted light is determined by to decode the bead. The coded bead may be structured a series of alternating light transmissive and opaque sections, with relative positions, widths and spacing resembling a 1D or 2D bar code image. To decode the image, the alternating transmissive and opaque sections of the body are scanned in analogous fashion to bar code scanning. The coded bead may be coated or immobilized with a capture or probe to effect a desired bioassay. The coded bead may include a paramagnetic material. A bioanalysis system conducts high throughput bioanalysis using the coded bead, including a reaction detection zone and a decoding zone.