High process yield rates of thermoplastic nanofluidic devices using a hybrid thermal assembly technique

Abstract

Over the past decade, thermoplastics have been used as alternative substrates to glass and Si for microfluidic devices because of the diverse and robust fabrication protocols available for thermoplastics that can generate high production rates of the desired structures at low cost and with high replication fidelity, the extensive array of physiochemical properties they possess, and the simple surface activation strategies that can be employed to tune their surface chemistry appropriate for the intended application. While the advantages of polymer microfluidics are currently being realized, the evolution of thermoplastic-based nanofluidic devices is fraught with challenges. One challenge is assembly of the device, which consists of sealing a cover plate to the patterned fluidic substrate. Typically, channel collapse or substrate dissolution occurs during assembly making the device inoperable resulting in low process yield rates. In this work, we report a low temperature hybrid assembly approach for the generation of functional thermoplastic nanofluidic devices with high process yield rates (>90%) with a short total assembly time (16 min). The approach involves thermally sealing a high Tg (glass transition temperature) substrate containing the nanofluidic structures to a cover plate possessing a lower Tg. Nanofluidic devices with critical feature sizes ranging between 25 – 250 nm were fabricated in a thermoplastic substrate (Tg = 104°C) and sealed with a cover plate (Tg = 75°C) at a temperature significantly below the Tg of the substrate. Results obtained from sealing tests revealed that the integrity of the nanochannels remained intact after assembly and devices were useful for fluorescence imaging at high signal-to-noise ratios. The functionality of the assembled devices was demonstrated by studying the stretching and translocation dynamics of dsDNA in the enclosed thermoplastic nanofluidic channels.

Thermoplastic nanofluidic devices for biomedical applications

“…This value was less than 60 m C/m 2 reported by Stein et al 109 and 214 m C/m 2 reported by Schoch et al 107 for glass-based nanoslits measured at pH 8. However, surface charge measurements performed in a nanoslit hybrid device – PMMA substrate bonded to oxygen plasma treated COC cover plate –|σ s | was 57.3 mC/m 2 85 . The difference in surface charge density was attributed to more carboxyl groups generated on COC compared to PMMA when treated under similar oxygen plasma conditions.…”

“…Furthermore, copolymers can be used as substrates for nanofluidic devices that have a range of physiochemical properties arising from differences in the ratio of monomeric components used in them. 85 …”

“…Although some reports have investigated this effect, more research must be done to show the effects of increased surface roughness on nanoscale fluid dynamics. 85, 102 …”

“…85 Device assembly was achieved by bonding an O 2 plasma treated cover plate to an untreated substrate at a temperature ~5°C lower than the T g of the cover plate. COC (T g = 75°C) was used as the cover plate for a PMMA (T g = 105°C) substrate due to its excellent optical transmissivity, low autofluorescence, 105, 106 low moisture uptake (< 0.01 %), high temperature tolerance, and chemical resistance.…”

High-strength thermoplastic bonding for multi-channel, multi-layer lab-on-chip devices for ocean and environmental applications

“…High-strength bonding is achievable by these processes at temperatures sufficiently low to minimise temperature-induced channel deformation. Nevertheless, polymer surface dissolution and softening may also lead to dimensional change or distortion (Uba et al 2015).…”