(314d) Pneumatically Driven 16 Channel Disposable Nucleic Acid Filter Device with Integrated Demultiplexing and Multiplexing

As the popularity of filter based nucleic acid extraction systems grows the need for regenerable or disposable filters and filter assemblies will follow. A unique advantage of filter based nucleic extraction systems is their ability to fully integrate and implement major extraction system components. Unlike their centrifugation centric counterparts the integrated soft lithography solutions don't require complex, power-hungry, poorly scalable centrifuges to separate NAs from the sample material. Instead, the solution is passed through a filter which provides a binding surface whereby NAs can be temporarily attached by means of a salt bridge. These NAs are later released in the presence of an elution buffer. This method, along with other solid state extraction schemes, has demonstrated extraction efficiencies comparable to those attained with a conventional centrifugation process(ref). A challenge presented by this type of system is the regeneration of the filter material. If proper elution and sterilization is not performed cross-contamination is almost guaranteed. This can be accomplished by means of sterilization assays and regeneration protocols. However, the additional resources required to implement such procedures, i.e. pumps, valves, solution storage, etc., can be undesirable. Additionally the filter material may have a limited number of regeneration cycles before its efficacy is compromised. This paper presents a novel solution that can act as a stand-alone device or can be integrated into a larger system. We propose a disposable or limited use filter ring containing 16 individual filters each addressable by means of pneumatically driven microvalves. The term ?ring? is used to describe the disposable filter material portion because the geometry of the reusable mux/demux portion requires that the filters be arranged in a circle or ring. The device offers a single input and single output. All demultiplexing and multiplexing of the solution is handled inside the device. By integrating demux/mux capabilities the device can be quickly integrated into any current single filter system. The only requirements for integration are: the necessary hardware connections, a reasonable tolerance for additional dead volume, and the supply of pneumatic selection lines. The device is constructed exclusively of four materials; polydimethylsiloxane or PDMS, silicone membrane, glass microfiber, and poly methyl methacrylate or PMMA. The PMMA is purely structural and does not contact the solution. The construction is a sandwich type. The device consists of individual isolated glass microfiber filters between PDMS slabs. This structure is compressed between the demux and mux subassemblies. The demux and mux assembly are mirror images and function identically. The control lines actuate both devices simultaneously. PMMA is used for even compression of the device by the clamping mechanisms. Also, a PMMA ring is used to direct compression of the device away from the microchannels, so as not to block the flow of solution, and towards the areas of potential leakage. The addressing scheme implemented for filter selection in the system is a based on a simple binary solution commonly used in electronic multiplexors. The pneumatic solution however, requires twice the number of control lines. This is due to the number of valves necessary to simply implement the demux/mux and the single pole single throw nature of the pneumatic valve. The relationship is as follows; where n is equal to the number of valves and f is equal to the number of filters f=2^(n/2). This relationship is very beneficial as the number of individual filters is increased. Note that n must be an even nonzero value. The device has shown to be easily integrated into existing systems providing a quickly disposable, individually addressable, multiple filter solution for solid state NA extraction.