Manipulation of mammalian cells using a single-fiber optical microbeam

Abstract

Optical scissors and tweezers have been tools of the biologist for over two decades.^{1, 2} Recently, the application of optically based micromanipulation has led to an explosion of new applications. In particular, optical tweezers and scissors have had a major impact on the fields of biophysics^{3, 4} and colloidal science,⁵ with applications ranging from measurement of force at the single molecule level^{6, 7, 8, 9} to disease diagnosis¹⁰ to therapeutic applications¹¹ in the field of assisted reproductive therapy (ART). Recently, while optical tweezers have been shown to enhance and guide neuronal growth,^{12, 13} femtosecond laser scissors have been employed for axotomy of neurons, allowing measurement of the regeneration process.¹⁴ In contrast to the short working distance of the high numerical aperture (NA) microscope objectives, optical tweezers and scissors based on a single optical fiber will enable micromanipulation at much larger depths and thus open up additional avenues for biophysics and nanoscience research. While no report exists on single-fiber scissors, earlier attempts to trap in three dimensions using a single optical fiber have not been successful, even with a hemispherical lens built on the tip of fiber.^{15, 16} This failure is presumably due to the dominance of the scattering force in the axial direction. While particle trapping using a single fiber probe with an annular light distribution¹⁷ required balance of opposing optical and electrostatic forces, recently, pure-optical 3-D trapping was demonstrated using a tapered¹⁸ and axicon-tip fiber.¹⁹