ABSTRACT
The importance of optical traps in biology arose from the development of the single-beam gradient trap, or “optical tweezers,” in 1986 [1] (see PAPER 1.5). Optical tweezers have since been applied in cell biology [2] and in the rapidly expanding field of single-molecule research [3]. Optical forces produced by commonly available lasers lie in the piconewton (pN) range, which is just right to experiment with biological cells and individual molecules. Because most biological materials absorb only weakly in the near infrared region of the electromagnetic spectrum, Nd:YAG (λ = 1064 nm) lasers are well suited to optical tweezers applications in biology [2,4,5]. Optical forces generated by relatively inexpensive, diode-pumped lasers (>100 mW power) easily overcome the relatively weak forces associated with thermal agitation, gravity, and fluid flow and enable biological cells and microorganisms (including viruses, bacteria, sperms, red blood cells, and other mammalian cells) to be picked up and manipulated at will within aqueous media. However, the biggest impact in biology so far has been the ability to make ultra-high-resolution mechanical measurements on individual biological molecules. Optical tweezers are suitable for many studies in biology because they can readily produce forces of between 0.1 pN to 500 pN.
