Biophysics in reverse: Using blood cells to accurately calibrate force-microscopy cantilevers

We report on the refinement and validation of one of the earliest ideas of "reverse" biophysics: the use of individual red blood cells as reliable, ultrasensitive mechanotransducers. Our analysis is based on the numerical prediction of the force exerted by a micropipette-held red cell as it is pushed against a test object. Examining this red-cell transducer, in conjunction with a custom-built "horizontal" force microscope, we were able to soundly corroborate its utility, while at the same time, accurately calibrating the spring constants of atomic-force microscope cantilevers.