Research Highlight

Technique to measure tiny forces between particles, cells

doi:10.1038/nindia.2019.132 Published online 30 September 2019

When two surfaces come close to each other, a weak force, known as the Van der Waals force, comes into play. Such a surface force, formed because of molecular attractions over small distances, is manifested when a gecko sticks to a wall, for example. 

Indian physicists have devised a laser-based technique that can be used to measure such tiny forces between two particles1.

Several diseases are known to modify a cell’s surface. Such disease-induced surface modification may be captured using this method, making it potentially useful for detecting diseases such as malaria and cancer.  

Scientists from the Indian Institute of Science Education and Research in Kolkata, India, optically trapped a microscopic polystyrene particle that acted as a probe to measure the Van der Waals force. They then moved the probe particle close to the surface of a larger silica particle in a tiny volume of viscous fluid kept on a microscope cover slip.  

The researchers, led by Ayan Banerjee, measured how the presence of the silica particle’s surface influenced the motion of the probe particle. Although they measured the force between the two particles, it is a handy technique to measure the nature of any type of force between two particles or surfaces.

This work may be expanded to measure surface forces generated inside and outside of a cell. “Inside a cell, one can even study how surface forces influence the processes in which cells devour invaders such as pathogens, revealing how the intracellular environment behaves,” says Banerjee.


1. Kundu, A. et al. Measurement of Van der Waals force using oscillating optical tweezers. Appl. Phys. Lett. 115, 123701 (2019) doi: 10.1063/1.5110581