Aptamer optical switches: From biosensing to intracellular sensing

Aptamers are the evidence of the power and versatility of DNA. In the biosensing field, if the important properties of aptamers together with all the many different conformations they can adopt are coupled to the proper transduction system, an unthinkable amount of possibilities is open up to construct biosensing methods for, in principle, any imaginable target. Inspired by classical molecular beacons, by using the intrinsic property of aptamers of changing their conformation when binding to the target and the possibility of labelling and coupling them to other DNA sequences, nanomaterials or polymers, a large variety of "turn on" or "turn off" optical biosensing systems, can be developed. This review gives an overview of the recent works dealing with aptamers as optical switches in biosensing. Several optical approaches based on luminescence are considered, ranging from fluorescence, to chemi/bio luminescence, to plasmon field-enhanced fluorescence. The attractive combination of aptamer optical switches and nanomaterials is also discussed. Finally, the appealing and challenging application of aptamer optical switches to intracellular sensing and imaging is presented.