The technique of optical tweezers has been improved a lot since its invention, which extends the application fields of optical tweezers. Besides the conventionally used Gaussian beams, different types of ring beams have also been used to form optical tweezers for different purposes. The two typical kinds of ring beams used in optical tweezers are the hollow Gaussian beam and Laguerre-Gaussian （LG） beam. Both theoretical computation and experiments have shown that the axial trapping force is improved for the ring beams compared with the Gaussian beam, and hence the trapping stability is improved, although the transverse trapping forces of ring beams are smaller than that of Gaussian beam. However, no systematic study on the trapping forces of ring beam has ever been discussed. In this article, we will investigate the axial and transverse trapping forces of different types of ring beams with different parameters systematically, by numerical computation in which the ray optics model is adopted. The spherical aberration caused by the refractive index mismatch between oil and water is also considered in the article. The trapping forces for different objectives that obey the sine condition and tangent condition are also compared with each other. The result of systematical calculation will be useful for the applications of optical tweezers formed by different types of ring beams.
Lymphocyte function associated antigen-1 （CD11a/CD18, LFA-1） plays an important role in the structure of the immunological synapse and is required for efficient lysis of cytotoxic T lymphocytes （CTLs） and natural killer （NK） cells. To study the activation mode of LFA-1 on the NK cell surface, optical tweezers were used in the work. As an emerging technology, optical tweezers are widely used to manipulate microscopic objects and measure the forces of molecular interactions in the field of biological research. In our study, a new platform was constructed to study the single molecular behavior of receptor on cell surface using optical tweezers. Based on the platform, the interaction between an NK cell and a polystyrene microsphere coated with anti-LFA-1 antibody was observed. The result confirmed that the adhesion forces between an NK cell and a polystyrene bead were time-dependent. According to our findings, we propose that anti-LFA-1 antibody may cause the clustering of LFA-1 on NK cell surface. Cellular ＆ Molecular Immunology.
