Homogeneous sol-sol assay

Abstract

The present invention provides methods for detecting the presence of or determining the amount of a ligand in a fluid sample. The methods comprise providing a first reagent comprising a sol particle having a detectable physical property bound to the ligand or ligand analogue (in a competitive format) or a substance capable of specifically coupling with the ligand (in a sandwich format), providing a second reagent having a detectable physical property comprising a sol particle bound to a substance capable of specifically coupling with the ligand and/or ligand analogue, if present, combining the first reagent, second reagent and the fluid sample and detecting before, during or after the reaction, a change in the physical property of the sol particles, which provides a qualitative or quantitative indication of the ligand in the fluid sample. The reagents couple with one another as a function of the presence of the ligand in the sample to thereby produce a change in the physical property of the sol particles which is related to the degree of coupling of the reagents. The invention also provides a kit for detecting the presence of or determining the amount of a ligand in a fluid sample. The invention further provides immunological complexes having a detectable physical property.