Technique for mechanical measurements using optical scattering from a micropipette [cells application]

The authors propose an optical method using forward light scattering to measure the deflection of a micropipette from a normal contact force with a small elastic solid, and the damping coefficient of a small fluid sample through a dynamic interaction with the pipette. An analytical and experimental study of this sensor is performed and described for each property. Topics covered include: (1) forward light scattering technique for determining the diameter of a micropipette (using exact and simplified geometric interference theories); (2) deflection measurement and analysis on the pipette-sample system using the finite element method; and (3) equivalent damping coefficient and resonant frequency measurement of the pipette-fluid system and its numerical solution derived from the finite element model. A comparison of the experimental results and the analytical results is included to provide the means for analyzing the potential of this new method.