ИСТИНА

Laser tweezers (LT), also referred to as optical traps (OT), is a novel technology that has emerged in the 1970-s. It opened new possibilities to handle and manipulate without any mechanical contact the microparticles of different nature and to measure molecular-level (picoNewton scale) forces of the interaction between them and with the environment. Due to extremely wide area of potential applications of this technology it gained intensive development and many research groups went into designing new schemes and operation modes of LT and exploring their new application perspectives. Given the experience of long lasting scientific collaboration in the field of biophotonics between our laboratories, we decided to jointly enter this field of research and build two similar LT set-ups in Oulu and in Moscow for biophotonics applications. The initially set problem was to study the peculiarities of light scattering by non-spherical red blood cells (RBC) and their aggregates, and the biophysical mechanisms behind RBC interaction in the process of reversible aggregation. Measurements with the LT were backed with digital calculations of light scattering effects from nonspherical particles and extensive studies of RBC microrheology with other optical techniques, in particular, laser backscattering aggregometry (LBA) from whole blood samples, which we had been also developing for a number of years. In comparison with LT-assisted single cells level measurements, LBA yielded data averaged over millions of cells, this approach having its advantages and limitations. It is of fundamental interest to compare the information about the RBC interactions that can be obtained with LT and LBA. Implementation of these techniques into clinical practice has a perspective of drastic improvements in the health-care of patients suffering from cardio-vascular and various systemic diseases, like diabetes. The OT are formed with orthogonally polarized cw laser beams from two single mode diode pumped Nd:YAG lasers with the output power up to 250 mW. Large numerical aperture water immersion objective is used to tightly focus the laser beams and form two OT. The RBC trapping force can be varied in the range from 1 to 20 pN. Visual control of the trapped cells is implemented with a CMOS camera. We will present the latest results obtained with our LT devices including the measured RBC light scattering phase functions and the measured dependencies of the cells interaction forces on the content of the environmental medium. The presentation will be assisted with the real time video recordings of the cells interaction processes.