Research Highlight

How a microscopic bio-heat engine works

doi:10.1038/nindia.2016.113 Published online 31 August 2016

Physicists have designed a microscopic heat engine by optically trapping a colloidal bead in a bacterial bath1. The heat engine could potentially be used in nano-electromechanical and microfluidic devices.

A conventional macroscopic heat engine converts heat energy into mechanical work by confining a few cubic centimetres of gas between a moving piston and its walls.

To fabricate a similar heat engine on a microscopic scale, the researchers optically trapped a colloidal bead in a bacterial bath containing the soil-dwelling bacterium Bacillus licheniformis. Changes in laser intensities functioned as a piston, decreasing or increasing the space in which the bead was trapped.

The scientists varied the temperature of the bacterial bath by maintaining a flow of heat-exchanging fluid through a channel. At a specific laser intensity and a temperature of 290 kelvin, the bacteria were active but sluggish. When the laser intensity was increased and the temperature reached 313 kelvin, the bacteria became more active, which agitated and displaced the bead considerably from the trap centre and hence resulted in a broad distribution function and large work.

The cumulative work increased steadily with increasing bacterial activity. At its peak activity, the heat engine’s efficiency was almost an order of magnitude higher than passive engines, and a factor of two smaller than biological motors.

“This engine will help us understand biological motors, which operate with almost 100% efficiency without cycling the temperature in two reservoirs,” says lead researcher Ajay Sood from the Indian Institute of Science.

The authors of this work are from: Department of Physics and Biophysics Unit, Indian Institute of Science, International Centre for Materials Science and Sheikh Saqr Laboratory, Jawaharlal Nehru Centre for Advanced Scientific Research,  Bangalore, India.


1. Krishnamurthy, S. et al. A micrometre-sized heat engine operating between bacterial reservoirs.Nat. Phys. (2016) doi: 10.1038/NPHYS3870