Homogeneous sol-sol assay

A method for detecting the presence of a ligand in a fluid sample comprising

• (a) providing a first reagent comprising a sol particle having a visibly detectable physical property bound to the ligand;
• (b) providing a second reagent comprising a sol particle having a visibly detectable physical property bound to a substance capable of specifically coupling the ligand;
• (c) combining the first and second reagent in a solution so that the first and second reagents couple which gives the solution a different visibly detectable physical property than that of the first and second reagents prior to the combination;
• (d) adding the sample;
• (e) observing the physical property of the solution;
• (f) correlating the physical property to the presence or absence of ligand in the sample.

A method for detecting the presence of or determining the amount of multiple ligands in a fluid sample wherein the method comprises

• (a) providing a first reagent for each of said multiple ligands comprising a sol particle bound (i) to the ligand or (ii) to a substance capable of specifically coupling with the ligand;
• (b) providing a second reagent for each of said multiple ligands comprising a sol particle bound to a substance capable of specifically coupling with the ligand, the sol particles of the first and second reagents corresponding to each of said ligands having a unique detectable physical property which is distinguishable from the physical properties of the sol particles corresponding to the other ligands;
• (c) combining the reagents with the fluid sample, said reagents coupling with one another as a function of the presence of the multiple ligands in the sample to thereby produce a change in the physical properties which is related to the degree of coupling of the reagents;
• and
• (d) detecting or determining during or after the reaction the physical property of the sol particles which detection or determination provides a qualitative or quantitative indication of the multiple ligands in the fluid sample.