The "optical funnel". A technique for measuring a microorganism's power

A novel and potentially useful optical technique called an "optical funnel" has been developed. The technique utilizes a system in which a microorganism is suspended by equilibrium between the medium flow and the radiation pressure applied in the opposite direction. At equilibrium, i.e., when the force of the laser pressure is equal to the force of the moving stream, the microorganism is captured. At this point, it has the ability to escape on its own power. Since the force applied to the microorganism is calculated on the basis of a ray-optics model, it is possible to measure the magnitude of the microorganism's power. A Trachelomonas volvocina cell was determined to have a power of ∼1 pN. This technique is superior to the laser trapping technique, which is currently used in these determinations, since it is possible to capture numerous organisms in a single experiment, thus allowing the calculation of the average power for an organism with minimal effort, in terms of repetitive samplings and measurements.