High-resolution permanent photoresist laminate TMMF for sealed microfluidic structures in biological applications

Abstract

We demonstrate the use of photosensitive epoxy laminate TMMF S2045 for the fabrication and sealing of tapered microfluidic channels. The 45 μm thick resist enables the fabrication of shallow sealed cavities featuring extreme aspect ratios of less than 1:40 (h = 45 μm, w = 2000 μm). It also provides high resolution and enables minimum feature sizes of 10 μm. For the fabrication of free-standing structures, an aspect ratio of up to 7:1 was achieved. The dry-film photoresist can be applied easily by lamination onto structured substrates. The total thickness variation of the resist across a 100 mm wafer was determined to be less than ±0.6 μm. Process parameters for the fabrication and sealing of various micro-channels are discussed and optimized in this paper. The main focus was to minimize thermal impact during lamination, soft-bake, exposure and post-exposure bake, which could lead to lid sagging or channel clogging due to liquefaction of uncured resist. We tested TMMF according to ISO 10995-5 and found it to be non-cytotoxic, enabling its use for biological applications. Swelling of less than 5% for incubation of the dry-film resist in several biologically relevant solvents, buffers and cleaning solutions was observed.

Screening ion-channel ligand interactions with passive pumping in a microfluidic bilayer lipid membrane chip

“…A second layer of TMMF S2030 was laminated over the first layer at 45 C to define the BLM aperture. 32 To make the surface hydrophobic (for stable bilayers and control of droplet surface tension), the chips were exposed to a CF 4 plasma, at a gas ratio of 2% O 2 and 98% CF 4 , 50 W and 50 mTorr pressure for 2 min. The contact angle for water on the treated TMMF surface was around 115 .…”

“…Only those channels that insert with the intracellular side facing the trans (pH 4.0) chamber will be active; channels inserting with the intracellular side facing the cis (pH 7.4) chamber will be functionally silent. 16,17,32 Characteristically, KcsA displays longlived "quiet" or closed intervals and exhibits low open probabilities, 16 hence we used the noninactivating KcsA mutant (E71A) where the long closures have been abolished and the open probability is >90%. 40 Single-channel KcsA-E71A traces in symmetrical 150 mM KCl solutions were obtained, demonstrating proteoliposome fusion with the aperture-suspended bilayer and bilayer incorporation of a non-toxin ion channel.…”

Scalable micro-cavity bilayer lipid membrane arrays for parallel ion channel recording

“…After stripping the AZ9260 resist and cleaning, the cavity was defined from a single layer of TMMF S 2055 dry-film resist (S200 series, TOK, Kanagawa, Japan), laminated onto the wafer at 80 • C followed by soft baking for 5 min at 70 • C [19]. The protective foil was removed before soft baking and the resist exposed in a mask aligner (EVG 620) using an i-line filter for 40 sec at 11 mW/cm 2 .…”

“…The protective foil on top of the dry film resist affects the smoothness of the aperture [19] because the foil scatters the exposure light causing roughness in the resist. In addition, the metal chuck of the mask aligner can also reflect light to some extent and may affect the smoothness of the aperture wall.…”

Rounding of Negative Dry Film Resist by Diffusive Backside Exposure Creating Rounded Channels for Pneumatic Membrane Valves

“…DFR technology is competitive to standard SU-8 processes in respect to feature size [12,13] and consistent height of the resist over a large substrate area [14,15]. Nevertheless, fabrication of round shaped channels in DFR technology for the realization of microfluidic membrane valves and pumps is not feasible yet, other than for SU-8 technology [16].…”