Rapid prototyping of poly(methyl methacrylate) microfluidic systems using solvent imprinting and bonding

Abstract

We have developed a method for rapid prototyping of hard polymer microfluidic systems using solvent imprinting and bonding. We investigated the applicability of patterned SU-8 photoresist on glass as an easily fabricated template for solvent imprinting. Poly(methyl methacrylate) (PMMA) exposed to acetonitrile for 2 min then had an SU-8 template pressed into the surface for 10 min, which provided appropriately imprinted channels and a suitable surface for bonding. After a PMMA cover plate had also been exposed to acetonitrile for 2 min, the imprinted and top PMMA pieces could be bonded together at room temperature with appropriate pressure. The total fabrication time was less than 15 min. Under the optimized fabrication conditions, nearly 30 PMMA chips could be replicated using a single patterned SU-8 master with high chip-to-chip reproducibility. Relative standard deviations were 2.3% and 5.4% for the widths and depths of the replicated channels, respectively. Fluorescently labeled amino acid and peptide mixtures were baseline separated using these PMMA microchips in <15s. Theoretical plate numbers in excess of 5000 were obtained for a approximately 3 cm separation distance, and the migration time relative standard deviation for an amino acid peak was 1.5% for intra-day and 2.2% for inter-day analysis. This new solvent imprinting and bonding approach significantly simplifies the process for fabricating microfluidic structures in hard polymers such as PMMA.

Figure 1

PMMA microchip fabrication process. (A, B) PMMA substrates have a layer of acetonitrile deposited on the surface. (C) A patterned SU-8 template on glass is pressed down on a solvent-softened PMMA surface. (D) An unpatterned glass slide is contacted to the other acetonitrile-coated PMMA substrate. (E) The SU-8 patterned template is removed, leaving a PMMA piece with imprinted microchannels, (F) and the glass slide is removed from the PMMA cover plate. (G) The cover plate is placed atop the imprinted substrate and held with applied pressure for 30 s to seal the channels. (H) Microchip design; the injector offset is not drawn to scale.

Figure 2

SEM images depicting the effect of imprinting time on the channel structure. Imprinting times were (A) 6, (B) 10, (C) 20, (D) 30, and (E) 60 min. (F) Schematic of imprinted dimensions: channel height (h), channel edge ridge height (h′), channel width at the bottom (w), and channel width at the top (w′). Substrates are inverted relative to their orientation in bonded devices.

Figure 3

Top-view SEM of an imprinted channel injection region.

Figure 4

Effect of solvent exposure time on bonded channel structures. SEM images of bonded channel cross sections for acetonitrile exposure times of (A) 0.5 and (B) 2 min.

Figure 5

Electrophoretic separation of FITC-labeled (A) amino acids and (B) peptides in rapidly prototyped PMMA microchips, using 10 mM Tris buffer (pH 8.5) with 0.5% (w/v) HPC. Peaks in both separations were identified by spiking; no FITC peak was observed in (B) because the labeling reaction was allowed to proceed to completion [18].