Tunable-Volume Handheld Pipette Utilizing a Pneumatic De-Amplification Mechanism

Abstract

We present the design, analysis, and validation of a tunable-volume handheld pipette that enables precise drawing and dispensing of ml and μl liquid volumes. The design builds upon the standard mechanism of a handheld micropipette by incorporating an elastic diaphragm that de-amplifies the volume displacement of the internal piston via compression of an entrapped air volume. The degree of de-amplification is determined by the stiffness of the elastic diaphragm and the amount of entrapped air. An analytical model of the diaphragm mechanism is derived, which guides how to achieve linear deamplification over an extended range where leading-order nonlinear contributions are significant. In particular, nonlinearities inherent in the mechanical behavior of the diaphragm and entrapped air volume may exactly cancel one another by careful design of the pipette's parameter constants. This linearity is a key attribute for enabling the pipette's tunable volumetric range, as this allows diaphragms with different stiffnesses to be selectively used with a conventional linearstepping piston mechanism. Design considerations regarding the range, accuracy, and precision of the proposed pipette are detailed based on the model. Additionally, we have constructed a handheld prototype that uses a planar latex sheet as the diaphragm. Our pipetting experiments validate the derived model and exhibit linearity between the piston stroke and drawn liquid volume. We propose that this design enables a single handheld mechanical pipette to achieve drawing and dispensing of liquids over a 1μl-10ml range (i.e., the range of the entire micropipette suite), with volumetric resolution and precision comparable to commercially available counterparts.