Optical Tweezers Grab Blood Cells

May 22, 2013

The technology for manipulating single molecules in the nano and micro scale has been around since the 1980s. Holographic or diffractive optical tweezers are continuous-wave micro laser beams whose photons, when tuned to a specific frequency and energy density, can influence a certain type of matter due to weak interactions between photons. A team from University of Science and Technology of China, led by Yin-Mei Li, has been experimenting with infrared optical tweezers that can manipulate red blood cells, about 10 micrometers in size, in living organisms.

In a report published by the journal Nature Communications, the team explains their manipulation of red blood cells (RBCs) in sub-dermal capillaries on the ear of a mouse.

In a series of experiments, the team showed they could use optical tweezers to move individual RBC in capillaries, recreating blood clots as well as deconstructing blockages cell by cell. Currently, the laser can only penetrate 40 micrometers deep, but more intense lasers, combined with advanced optics, will increase this depth in the future.

This type of non-invasive vessel clearance has never been done on a live specimen. The team was able to determine the trap stiffness for controlling a RBC in a capillary, a calculation that depends on the wavelength; polarization; intensity of the focused laser; the micro object's aperture, size, and shape; as well as the refractive index of the particle and medium. The energy density needed for interactions between infrared optical tweezers and red blood cells is in the order of 10^7J/cm3.

This method of manipulating living cells has potential for some exciting experimentation and research. New physiological information could be obtained concerning live cellular dynamics about processes that are still mysterious. The tweezers could also be used to study cellular pathology by keeping cells still and watching diseases develop under a microscope. As photon scattering is prevented and lasers penetrate deeper, this non-invasive technique could be used to relieve blockages in bigger blood vessels like veins and arteries in humans.

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