Detection of microviscosity by using uncalibrated atomic force microscopy cantilevers

In this letter, we provide evidence that the vibrating resonance frequency of an uncalibrated atomic force microscope cantilever can be precisely related to the viscosity of the fluid in which it is immersed, independent of any knowledge of the cantilever s geometry and spring constant. Reverse geometry, density, and spring constants of a cantilever immersed in a fluid of known viscosity can be recovered with ease. The methods for monitoring viscosity we propose are of relevance to all biorheologic and microfluidic applications where functionalized cantilevers have to be used, and a simple, yet reliable nondestructive procedure is called for.