Strategies for Optical Trapping in Biological Samples: Aiming at Microrobotic Surgeons

Optical trapping and manipulation of objects down to the Angstrom level has revolutionized research at the smallest scales in all natural sciences. The flexibility of optical trapping methods facilitates real-time monitoring of the dynamics of biological processes in model systems and even in living cells. Different optical trapping and manipulation approaches allow displacement of nanostructures with subnanometer precision and force measurements with femtonewton precision. Due to inherent constraints of optical methods, most optical trapping experiments are performed in water or simple aqueous solutions. However, in recent years, there is an ever-growing interest of shifting from simple aqueous media towards more biologically-relevant media. Precise optical trapping and manipulation, combined with state-of-the-art microfabrication, will enable the development of microrobotic "surgeons" with tremendous potential for biomedical and microengineering applications. This review introduces the basics of optical trapping and discusses its applications for biological samples, with focus on trapping in biological media and strategies for overcoming the challenges of optical manipulation in complex environments as a stepping-stone for microrobotic "surgeons."