Super-paramagnetic particles are used extensively in diagnostics and other research applications for the purification of cells, biomolecules and assays. Here, we demonstrate full 3D optical manipulation of such sub-micrometer sized particle using optical tweezers. We report three types of anomalous behavior of such a trapped particle. Firstly, the analysis of particle motion recorded by the quadrant photodiode reveals spikes in the total detected intensity that are formed by a set of very fast oscillations. Secondly, the dependence of trap stiffness on the laser power deviates from the expected linear increase for higher trapping powers. And further, such a particle cannot be optically trapped above certain trapping power threshold. We speculate that these effects are caused by particle internal structure and by its heating.

Date Published: 16 September 2014
PDF: 8 pages
Proc. SPIE 9164, Optical Trapping and Optical Micromanipulation XI, 916436 (16 September 2014); doi: 10.1117/12.2062148

Published in SPIE Proceedings Vol. 9164:
Optical Trapping and Optical Micromanipulation XI
Kishan Dholakia; Gabriel C. Spalding, Editor(s)