Photophysical approaches to responsive optical probes

Responsive optical probes play a vital role in following and understanding biological events. In this review, we focus on the use of lanthanide complexes as molecular probes, as they offer many advantages in imaging and assays, particularly when used in time-gated protocols. We describe systems that illustrate the key photophysical approaches to achieving analyte-dependent signal modulation. In summary, this signal modulation can be achieved through changes either in the coordination sphere of the lanthanide or in the pathway of sensitized emission. In conclusion, we describe the main challenges to be overcome in the field of responsive probes, mainly the effective determination of concentrations in vivo and the development of probes with temporal responses adequate to follow fast processes.