Toward 3D printed suspended microchannel resonators

Abstract

Biosensing properties like mass, density and stiffness on a single cell level can help diagnose diseases. Mass sensing of cells and subcellular components is typically performed with resonant microstructures. Recently such microstructures were fabricated using an emerging 3D printing technique called two-photon polymerization (2PP) contrary to conventional lithography-based fabrication. The suspended microchannel resonator (SMR) is such a resonant microstructure with an embedded fluidic channel for buoyant mass sensing, which has not yet been fabricated using 2PP. This work aims to 3D print an SMR with a sufficient mass resolution to detect the buoyant mass of E. Coli bacteria (175 fg in water). It was realized by first characterizing the damping in 3D printed polymer microbeam resonators for a better understanding of dominating damping sources. Followed by maximizing their quality factor and fabricating a prototype 3D-printed SMR. The characterized devices set a record-breaking standard for damping of polymer microbeam resonators: Cantilevers and bridges approached quality factors of 1000 and tensile stressed narrow bridges achieved a quality factor of 1819. These polymer resonators were dominated by bulk friction damping, but still had a mass resolution advantage over similar silicon-based devices when working in lower quality factor (Q < 1000) conditions, due to the low mass density of the polymer. Subsequently, prototypes of the suspended microchannel resonator were fabricated with multi-scale 3D printing containing a plug-and-play connection to fluidics and measurement equipment. Their theoretical mass resolution was estimated to be ≤ 60 fg, which is sensitive enough to detect E. Coli bacteria and compete with conventional fabricated SMRs. This paves the path towards actual biosensing 3D printed SMRs with the capabilities of lithography-based fabricated devices but with additional design and fabrication flexibility.