Strategy for photostable proximity bioassays using lanthanides.

We report initial findings for research aimed at creating photostable lanthanide chelate reporters for proximity assays. These reporters take advantage of the nanometer-scale distance dependence of fluorescence enhancement for molecules in the vicinity of noble metal nanoparticles and also capitalize on some unique properties of lanthanide chelates. This approach promises to lead to proximity assays that do not suffer from photobleaching and offer very high on/off enhancement ratios. Results for lanthanide chelates on silver island films and in colloidal suspensions are reported. Enhancement factors range from 1 to 2 orders of magnitude, with larger enhancements for strongly quenched lanthanides.