Microfabrication Process Development for a Polymer-Based Lab-on-Chip Concept Applied in Attenuated Total Reflection Fourier Transform Infrared Spectroelectrochemistry

Noah Atkinson; Tyler A Morhart; Garth Wells; Grace T Flaman; Eric Petro; Stuart Read; Scott M Rosendahl; Ian J Burgess; Sven Achenbach

doi:10.3390/s23146251

Microfabrication Process Development for a Polymer-Based Lab-on-Chip Concept Applied in Attenuated Total Reflection Fourier Transform Infrared Spectroelectrochemistry

Sensors (Basel). 2023 Jul 8;23(14):6251. doi: 10.3390/s23146251.

Authors

Noah Atkinson¹, Tyler A Morhart², Garth Wells², Grace T Flaman³, Eric Petro¹, Stuart Read⁴, Scott M Rosendahl⁴, Ian J Burgess³, Sven Achenbach¹

Affiliations

¹ Department of Electrical and Computer Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada.
² Synchrotron Laboratory for Micro and Nano Devices, Canadian Light Source Inc., Saskatoon, SK S7N 2V3, Canada.
³ Department of Chemistry, University of Saskatchewan, Saskatoon, SK S7N 5C9, Canada.
⁴ Mid Infrared Spectromicroscopy Facility, Canadian Light Source Inc., Saskatoon, SK S7N 2V3, Canada.

Abstract

Micro electro-mechanical systems (MEMS) combining sensing and microfluidics functionalities, as are common in Lab-on-Chip (LoC) devices, are increasingly based on polymers. Benefits of polymers include tunable material properties, the possibility of surface functionalization, compatibility with many micro and nano patterning techniques, and optical transparency. Often, additional materials, such as metals, ceramics, or silicon, are needed for functional or auxiliary purposes, e.g., as electrodes. Hybrid patterning and integration of material composites require an increasing range of fabrication approaches, which must often be newly developed or at least adapted and optimized. Here, a microfabrication process concept is developed that allows one to implement attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and electrochemistry on an LoC device. It is designed to spatially resolve chemical sensitivity and selectivity, which are instrumental for the detection of chemical distributions, e.g., during on-flow chemical and biological reaction chemistry. The processing sequence involves (i) direct-write and soft-contact UV lithography in SUEX dry resist and replication in polydimethylsiloxane (PDMS) elastomers as the fluidic structure; (ii) surface functionalization of PDMS with oxygen plasma, 3-aminopropyl-triethoxysilane (APTES), and a UV-curable glue (NOA 73) for bonding the fluidic structure to the substrate; (iii) double-sided patterning of silicon nitride-coated silicon wafers serving as the ATR-FTIR-active internal reflection element (IRE) on one side and the electrode-covered substrate for microfluidics on the back side with lift-off and sputter-based patterning of gold electrodes; and (iv) a custom-designed active vacuum positioning and alignment setup. Fluidic channels of 100 μm height and 600 μm width in 5 mm thick PDMS were fabricated on 2" and 4" demonstrators. Electrochemistry on-chip functionality was demonstrated by cyclic voltammetry (CV) of redox reactions involving iron cyanides in different oxidation states. Further, ATR-FTIR measurements of laminar co-flows of H₂O and D₂O demonstrated the chemical mapping capabilities of the modular fabrication concept of the LoC devices.

Keywords: Lab-on-Chip (LoC); UV lithography; attenuated total reflection Fourier transform infrared spectromicroscopy (ATR-FTIR); bonding; electrochemistry; micro electro-mechanical systems (MEMS); microfabrication; polydimethylsiloxane (PMDS).

Grants and funding

This work was funded by Discovery Grants from the Natural Science and Engineering Research Council (NSERC) of Canada. N.A. and G.T.F. acknowledge a Fellowship from the NSERC CREATE to INSPIRE program. G.T.F. acknowledges funding from the NSERC CGS-M program. Research described in this paper was performed at the SyLMAND and mid-IR beamlines of the Canadian Light Source (CLS). The CLS is supported by the Canada Foundation for Innovation, Natural Sciences and Engineering Research Council of Canada, the University of Saskatchewan, the Government of Saskatchewan, Western Economic Diversification Canada, the National Research Council Canada, and the Canadian Institutes of Health Research.