An experimental device, based on the optical tweezers technique, has been developed as a versatile tool for the realization of stable three-dimensional optical trapping and manipulation of microscopic particles, with dimensions ranging from 300nm to 10μm. It consists of an optical microscope (Nikon ME 600) and a coupled laser beam, which is tightly focused by a high numerical aperture (N.A.=1.25) objective. The trap was utilized in the focus of a near infrared cw diode laser beam (Vector Tech.), emitting at 810 nm with an output power of ~50 mW. The power of the trapping laser was enough to produce a stable trap since ~10mW where delivered on the focus of the objective. The wavelength of the laser beam was selected such that damage of trapped microparticles and especially biological cells was reduced to minimum. No optical destruction of the trapped cells was observed whatsoever. The optical tweezers device was developed in such a way that trapping of sub-cellular organelles was also possible. To achieve further manipulation of microparticles or biological cells a second laser beam has been introduced to the unit, to achieve the excitation of the trapped particles. The wavelength of the excitation beam was selected according to the absorption characteristics of the studied chromophores of the particles. In the frame of this study a cw Ar+ emitting at 514 nm has been used. Using this configuration the emission of trapped polystyrene microspheres has been observed. Photons were collected with an optical fiber through the eyepiece of the microscope, spectrally resolved with a spectrograph and detected by a diode array. Destruction of biological cells has been also observed. Further development of our setup, with the addition of time resolved fluorescence studies, will allow us to study the kinetics and dynamics of biological cells, as well as the underlying mechanisms that govern them.
(EN)
University of Crete
