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. read more