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."