Discrete Femtolitre Pipetting with 3D Printed Axisymmetrical Phaseguides

The capacity to precisely pipette femtoliter volumes of liquid enables many applications, for example, to functionalize a nanoscale surface and manipulate fluids inside a single-cell. A pressure-controlled pipetting method is the most preferred, since it enables the widest range of working liquids. However, precisely controlling femtoliter volumes by pressure is challenging. In this work, a new concept is proposed that makes use of axisymmetrical phaseguides inside a microfluidic channel to pipette liquid in discrete steps of known volume. An analytical model for the design of the femtopipettes is developed and verified experimentally. Femtopipettes are fabricated using a multi-scale 3D printing strategy integrating a digital light processing printed part and a two-photon-polymerization printed part. Three different variants are designed and fabricated with pipetting resolutions of 10 picoliters, 180 femtoliters and 50 femtoliters. As a demonstration, controlled amounts of a water-glycerol mixture were first aspirated and then dispensed into a mineral oil droplet. Introducing axisymmetrical phaseguides in microfluidic channels enables unprecedented liquid dosing resolution for pressure-controlled pipetting at the femtoliter scale. Leveraging a unique 3D printing method combining digital light processing and two-photon-polymerization, three femtopipette designs are demonstrated, achieving discrete pipetted volumes down to 50 femtoliters. This approach holds great promise as a multifunctional tool in micro-engineering, micro-chemistry, and micro-biology.image

Automated summary

This work proposes a new concept of pipetting liquid in discrete steps of known volume using axisymmetrical phaseguides in microfluidic channels. Three different variants of femtopipettes are fabricated using a multi-scale 3D printing strategy and demonstrated to achieve discrete pipetted volumes down to 50 femtoliters.