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Technique that links cell’s viscosity change to disease

Physicists have devised a technique that can help measure the viscosity of small volumes of different fluids1. This method could potentially be used to measure the viscosity of blood and even biological cells in which viscosity changes because of diseases.

To measure the viscosity of small volumes, the physicists from the Indian Institute of Science Education and Research (IISER) in Kolkata, India, led by Ayan Banerjee, immersed two polymer particles in water or in a mixture of water and glycerol. The particles, smaller than the diameter of a biological cell, were then trapped using laser light. A distance of about a hundredth of the thickness of a human hair separated the particles.

One of the particles, defined as control, was exposed to laser light, which made it to vibrate at different frequencies. The control particle then induced vibration of the other particle known as probe. When the control particle vibrates at a particular frequency, the probe particle’s vibration reaches its maximum value.

Such interactions of the two particles depend on the viscosity of the fluid in which they are suspended and optically trapped. This, in turn, helps measure the viscosity of the fluid.

Since the particles are smaller than a biological cell, it is possible to measure the viscosity of a cell by inserting them inside a cell, says co-researcher Subhajit Paul.

In the future, this technique can help detect cellular viscosity changes caused by blood disorders such as sickle-cell anemia and even viral infections, says lead researcher Banerjee.



  1. Paul, S. et al. Two-point active microrheology in a viscous medium exploiting a motional resonance excited in dual-trap optical tweezers. Phys. Rev. E. 97, 042606 (2018)

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