(314i) A Masked Corona Discharge Method for Selective Bonding in PDMS for Microfluidic Applications

Multi-layer PDMS devices are commonly used for microfluidic applications, and the method for bonding the several layers together has an impact on determining the possible uses for the device. Surface activation bonding methods such as oxygen plasma treatments and corona discharge methods have proven to supply ample adhesion between layers while having minimal adverse effect on the microfluidic device capabilities. This work examines an enhancement to corona discharge bonding methods by using a selective mask to bond only desired portions of the PDMS layers with applications in improving on-chip pneumatic valves and creating zero dead-volume channels and reservoirs.

Corona discharge bonding operates by creating hydrophilic, chemically active functional groups on the PDMS surface that bind to other activated groups when contacting another treated surface. Covering the PDMS layer to be bonded with a masking material during corona discharge treatment blocks areas from exposure to the corona plasma so that only exposed surfaces are activated. Subsequent removal of the mask and contact with another activated PDMS surface is shown to produce selective bonding, with the masked areas remaining unbound. Several masking materials are shown to be effective: Rubylith electrostatic film, Scotchcal Graphtec Instachange tape, mineral oil, and liquid spin-on glass. An acrylic sheet is also cut with a laser to provide a mask manifold to simultaneously mask multiple valve sites. The masked corona bonding method is shown to be effective in bonding PDMS to PDMS, glass, and other silicone materials.

This fabrication method is shown to be an efficient method to create passive check valves or pneumatically actuated valves in a three-layer PDMS device. The valves follow a similar design to other on-chip pneumatic valves, but the valve seat is masked from bonding to prevent it from becoming permanently closed while allowing the surrounding material to be permanently bonded in order for the valve to handle high pressures if needed.

Reservoirs and channels are created in a similar three-layer design with a pneumatic control layer separated from a fluidic layer by a thin membrane. Such features are demonstrated to consistently fill to a desired volume and subsequently empty completely, thus creating effectively zero dead-volume channels and reservoirs without the difficulty of fabricating channels and reservoirs with rounded edges in the vertical direction.

Masked corona discharge bonding in PDMS structures is used to create practical components in microfluidic devices with applications like trapping C. elegans worms and extracting nucleic acid from raw biological samples. This bonding method increases the capabilities of using PDMS as a material for rapid prototyping in microfluidic systems.