Research Highlight

Optical trap detects asymmetry in cells

doi:10.1038/nindia.2016.79 Published online 17 June 2016

An optical trap that employs a tightly focused laser beam can be used to detect misshapen red blood cells1. Since deformation of red blood cells can indicate the onset of diseases such as malaria and sickle-cell anaemia, this technique may be useful for early diagnosis.

Minute changes to the shapes of biological cells indicating underlying diseases cannot be detected by conventional microscopy. To detect shape asymmetry in cells, the researchers used a tightly focused laser beam as an optical trap. They then controllably deformed normal red blood cells by treating them with different saline solutions.

The technique measured shape asymmetry of the blood cells by exploiting their Brownian motion in saline solutions. Brownian motion is mostly translational for tiny symmetric objects, but any asymmetry in objects will induce a rotational component.

The cross-relation between rotational and translational Brownian motions is a sensitive measure of shape asymmetry. The scientists measured the cross-relation of these motions by trapping single deformed blood cell in the optical trap and comparing the motion with that of normal symmetric red blood cells.

The cross-relation differed substantially between symmetric and asymmetric red blood cells. Unlike the asymmetric red blood cells, the normal red blood cells did not show rotational motion.

“Besides detecting asymmetry in red blood cells, this technique could be used to reveal asymmetry of microscopic particles such as polystyrene beads and gold rods,” says lead researcher Ayan Banerjee.


1. Roy, B. et al. Using Brownian motion to measure shape asymmetry in mesoscopic matter using optical tweezers. Soft Matter 12, 5077–5080 (2016)