Toward single-metal-ion sensing by Förster resonance energy transfer.

Here we describe progress toward our objective of detecting single nonfluorescent hydrated metal ions. Single-ion detection represents detection and spectroscopy at the ultimate sensitivity level of approximately 1.6 x 10(-24) M. Achieving this goal would provide a breakthrough in analytical science and allow much more detailed insight into sensor-ion interaction than that available with conventional bulk detection methods. We combine recent advances in confocal microscopy with the sensitivity and the noninvasive nature of fluorescence by analyzing Förster resonance energy transfer between sensor fluorophores and transition metal ions.