This technology is a highly sensitive tethered-bead immune sandwich assay. Analyte molecules are captured between two antibodies, a capture antibody and a detection antibody. The capture antibody on a micron-size bead binds analyte from a sample fluid. The bead-captured analyte is then exposed to a “detection” antibody that binds to the bead-captured analyte, forming a “sandwich”. The sandwiched analyte-bead complex then connects to a flexible polymer (such as DNA) anchored on a solid surface to form tethered particles. Binding the analyte-bead complex to a flexible polymer forms tethered particles and may be done, for example, by streptavidin biotin. Motion of the tethered beads easily identifies bound analyte. The tethered beads are quantified using low-magnification light microscopy. Prior enhanced sensitivity tethered bead technologies require expensive and cumbersome detection equipment. This assay is inherently single molecule, low background, and works with simple inexpensive imaging formats, but is automatable and potentially adaptable to portable technologies. A prototype design using prostate specific antigen (PSA) shows detection sensitivity of ~.03ng/ml, compared with normal PSA sensitivity of ~ 4ng/ml. Design refinements further improve sensitivities.