Patent ID: 8101424

Claim:
A biosensing method for measuring concentration of an analyte that induces colloidal aggregation, the method comprising: (a) preparing small metallic colloids comprising a metal and at least partially coated with a binding component having an affinity for the analyte, and wherein the small metallic colloids are sized to scatter light according to the Rayleigh theory and range from 10 nm to 40 nm; (b) contacting the small metallic colloids with an analyte that has an affinity for the binding component to form an analyte/binding component complex, wherein the analyte has the ability to bind to multiple binding components forming aggregates of metallic colloids; and (c) measuring the change in intensity of scattered light from small metallic colloids relative to the intensity of scattered light measured for aggregates of metallic colloidals when exposed to electromagnetic radiation at a frequency that is absorbed and scattered, wherein the intensity of the scattered light is measured at two angles relative to the incident light and a change of the ratio is determined between the measured values at the two angles, and wherein the value of the ratio decreases as aggregation increases.