Development of Precision Optical Traps for Single Molecule and Motor Protein Research

Optical traps have become an important instrument for investigating systems and processes at the micro- and nanoscale, particularly within biology where manipulation of biological systems from DNA to cells has offered new insights to cellular processes. Using the inherent momentum of light, particles are trapped in the high intensity field of a focused laser beam thus allowing for the manipulation of microscopic particles. This paper discusses the current development of a state-of-the-art optical trap with increased sensitivity for the measurement of single molecule and motor protein mechanics. A common position sensing technique uses quadrant photodiodes to detect motion on the order of tens of nanometers. However, the measurement of positions and forces on a smaller level than previously attempted requires increased precision. Interferometric techniques provide one method to improve the spatial resolution to the order of nanometers or less. Furthermore, the use of feedback control offers the ability to easily adapt the optical trap to the particular experiment being conducted. In addition, optical traps can apply torque to trapped objects for the study of rotary mechanics when the trapping laser has orbital angular momentum. Methods for generating a laser beam with orbital angular momentum will be discussed.