Using laser tweezers, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with tangential surface anchoring. The interactions overcome the Brownian motion when the interparticle separation ${\overrightarrow{\mathbf{r}}}_p$ is less than 3 particle diameters. The particles attract when the angle $\theta$ between ${\overrightarrow{\mathbf{r}}}_p$ and the uniform far-field director ${\widehat{\mathbf{n}}}_0$ is between 0° and $\approx 70°$ and repel when $75°\lesssim \theta \le 90°$. The particles aggregate in chains directed at $\approx 30°$ to ${\widehat{\mathbf{n}}}_0$ and, at higher concentrations, form complex kinetically trapped structures.

We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal polarizing microscopy.