Homogeneous competition assays
Homogeneous assays wherein an unlabeled analyte is detected by displacing a more weakly binding tracer from a binding partner are described. The tracer has signal generating properties which differ when bound or unbound to the binding partner.
1 . A method to assay for the presence or concentration of an analyte which method comprises contacting a sample to be tested for said presence or concentration of analyte with a binding partner for said analyte, wherein said binding partner is coupled to a tracer
wherein the affinity of the tracer for the binding partner is at least 10-fold weaker than the affinity of the analyte for said partner; and
wherein an intrinsically detectable property of the tracer is altered when said tracer is displaced from said binding partner; and
determining the presence or amount of the change in said detectable property of the tracer,
whereby the presence or concentration of the analyte in said sample is determined.
2 . The method of claim 1 in which the intrinsic property that changes is fluorescence, or NMR signal.
3 . The method of claim 1 , which is performed intracellularly in a living cell.
4 . A kit for performing the method of claim 1 , which kit comprises, in suitable containers, a binding partner for the analyte and a tracer which has an affinity for the binding partner at least 10-fold weaker than that of the analyte and wherein said tracer has an intrinsically detectable property which changes upon displacement from the binding partner, along with instructions for performing the assay.