Patent ID: 7790392

Claim:
A homogenous assay method for measurement of biological activity, its modulation or analyte concentration of a sample, comprising a) bringing a sample, a first group, a second group and optionally a third group, in contact with each other to obtain an assay mixture, b) allowing the assay mixture to react, c) bringing the third group in contact with the assay mixture if it was not brought in contact with the assay mixture in step a), d) allowing the third group to react with the assay mixture if it was brought in contact with the assay mixture in step c), e) exciting a donor, and f) measuring a sensitized emission of an acceptor, wherein i) said first group comprises an acceptor, which acceptor is a short lifetime fluorescent compound capable of energy transfer, and ii) said second group comprises a quencher, which quencher is capable of energy transfer from an acceptor, and iii) said third group comprises a donor for energy transfer to said acceptor, which donor is an up-conversion fluorescent compound, a long-lifetime fluorescent compound or an electrogenerated luminescent compound; and said first group comprises a tag, said third group comprises a binder, and said binder has a high affinity for binding to said tag; and said sensitized emission of said acceptor is fluorescence brought about by exciting the donor resulting in energy being transferred from the donor to the acceptor, such that the increase or decrease, respectively, of fluorescence of said acceptor due to the decrease or increase, respectively, of energy transfer from said acceptor to said quencher resulting from lengthening or shortening, respectively, of the distance between said acceptor and quencher is measured.