Optical tools get new twist

Ashley N. Rice, ashley.rice@photonics.com

Conventional optical tools gently push and pull microscopic particles using light, but a new fiber-based system also gives microbiologists the ability to twist and turn samples.

The fiber optic spanner (the British term for wrench), developed at The University of Texas at Arlington, can precisely twist and turn microscale objects such as DNA strands in any direction and along any axis without moving any optical component, an ability that sets the virtual tool apart from others such as optical tweezers, which move objects backward and forward along a straight line.

An innovative fiber optic tool developed at UT Arlington allows scientists to twist and turn, as well as push and pull, single cells for cancer research. (1) Light-assisted controlled rolling of an object (dice). (2) Light-assisted controlled orientation of a fluorescently labeled cell, visualized in different orientations. (3) Stretching and untwisting a single DNA molecule by fiber optic spanner for faster sequencing or measuring torsional rigidity. Courtesy of Samarendra Mohanty, The University of Texas at Arlington.

The instrument consists of two flexible single-mode optical fibers, one that carries a 980-nm CW Ti:sapphire laser beam and one that is coupled to a 975-nm butterfly laser diode. Its beams strike opposite sides of the microscopic object, trapping and holding it in place, assistant professor of physics Samarendra Mohanty told BioPhotonics. If the fibers are slightly offset, the beams can impart a small twisting force, causing the object to rotate in place.

An intense laser beam creates just enough power to gently rotate microscopic particles using scattering forces, he said in a university release. The method already is used to perform optical tweezing, but lacks the control and versatility needed for working deep inside tissue.

Its precision was demonstrated by rotating and shifting human smooth muscle cells without damaging them. It can be used to manipulate other cells as well, Mohanty told BioPhotonics.

“It can be used for any cells, but we will be using [it] for discriminating breast cancer cells from their normal counterpart,” he said. “Also, our group is interested in rotating oocyte and stem cells for holographic imaging.”

The device could have use in both clinical and laboratory settings.

“For cellular diagnostic and imaging, it can be used in [the] near future,” he said. “However, it would require some efforts to establish its efficacy and improve the efficiency of analysis.”

The team would next like to “integrate holographic (quantitative phase imaging) with the fiber optic spanner for tomographic imaging of cells as well as nonbiological samples,” he said.

The findings were reported in Optics Letters (doi: 10.1364/OL.37.005030).