Patent ID: 8227260

Claim:
A method of detecting an interaction between a first antibody and an antigen, the method comprising: (a) contacting the antigen with a planar wave guide which contains the first antibody located at defined locations on the planar wave guide to form a first antibody-antigen complex, (b) contacting the first antibody-antigen complex with a second antibody with binding specificity for the antigen, to form a first antibody-antigen-second antibody complex, wherein the second antibody contains a gold particle label, (c) illuminating one or more of said defined locations on the planar wave guide by illuminating an edge of the wave guide, wherein the light illuminating said defined location is not evanescent light, and (d) detecting light scattered from the wave guide by the gold particle label, wherein the gold particle label has a diameter of from about 10 nm to about 140 nm and maximum absorption wavelengths of from about 525 nm to about 635 nm.