A fortuitous discovery by UK chemists has led to a new type of probe for protein interactions that could eventually be used for cellular imaging. 

Based on a chiral lanthanide complex, the probe emits circularly polarised light that inverts on protein binding - so monitoring the emitted light allows researchers to follow the interaction between the complex and the protein. Observing this luminescence is a way of studying the chirality of the system, explains David Parker, from Durham University, who led the team behind the research. 'The optical signal you observe is carrying information in its circular polarisation.' 

The team found that only one enantiomer of its europium and terbium complexes bound selectively to a drug binding site of the protein serum albumin, and that the luminescence changed dramatically. This is the first example of chiral inversion following non-covalent protein binding of an emissive probe, explains Parker. Potentially this technology could be used to track protein association in vivo in real time, he suggests.

The researchers have been seeking to develop responsive optical probes for a while and were delighted when they finally cracked it. 'We were genuinely surprised,' comments Parker. 'The binding free energy and kinetics have to be just right - we've been lucky.'

Ben Feringa an expert in chiral chemistry at the University of Groningen, the Netherlands, welcomes the research. He explains that 'the team has combined dynamic chirality at the molecular level with intrinsic circular polarised emission to study molecular binding events in a unique way. This finding might offer bright prospects in probing details of selective binding to biomacromolecules.' 

Russell Johnson