Since the introduction of micro total analytical systems (μTASs), significant advances have been made toward development of lab-on-a-chip platforms capable of performing complex biological assays that can revolutionize public health, among other applications. However, use of these platforms in low-resource environments (e.g. developing countries) has yet to be realized as the majority of technologies used to control microfluidic flow rely on off-device hardware with non-negligible size, cost, power requirements and skill/training to operate. In this paper we describe a magnetic-adhesive based valve that is simple to construct and operate, and can be used to control fluid flow and store reagents within a microfluidic device. The design consists of a port connecting two chambers on different planes in the device that is closed by a neodymium disk magnet seated on a thin ring of adhesive. Bringing an external magnet into contact with the outer surface of the device unseats and displaces the valve magnet from the adhesive ring, exposing the port. Using this configuration, we demonstrate on-device reagent storage and on-demand transport and reaction of contents between chambers. This design requires no power or external instrumentation to operate, is extremely low cost ($0.20 materials cost per valve), can be used by individuals with no technical training, and requires only a hand-held magnet to actuate. Additionally, valve actuation does not compromise the integrity of the completely sealed microfluidic device, increasing safety for the operator when toxic or harmful substances are contained within. This valve concept has the potential to simplify design of μTASs, facilitating development of lab-on-a-chip systems that may be practical for use in point-of-care and low-resource settings.
Coxiella burnetii is an intracellular bacterial pathogen that causes flu-like illness called Q-fever. C. burnetii extensively subverts host-cell vesicle traffic to create an acidic, lysosome-derived vacuole to support its intracellular replication. This is a unique evolutionary adaptation since lysosomal environment is hostile to most microbes. IFNγ signaling is essential for host protection against C. burnetii, but the underlying immune defense strategies are not well-defined. Using siRNAs to deplete IFNγ-induced genes, we identified that restriction of intracellular C. burnetii requires atleast two host factors, Indoleamine Dioxygenase 1 (IDO1) and Syntaxin 11 (STX11). IDO1 activity depletes tryptophan availability by catabolizing cellular tryptophan. This mechanism renders C. burnetii metabolically inactive since it is a tryptophan auxotroph, but is not sufficient to clear the infection. STX11 is a SNARE protein (Soluble NSF Attachment Protein Receptor) that promotes fusion of lysosome-derived organelles with target membranes. Bacterial replication as well as size of the C. burnetii-containing vacuole (CCV) are significantly increased in STX11-deficient cells. These cells also exhibited increased extracellular release of lysosomal proteins. STX11 over-expression reverses these phenotypes. Furthermore, STX11 accumulated in the CCV during infection. We hypothesize that STX11 regulates CCV-associated cargo-sorting and vesicle fusion events, leading to a sub-optimal vacuolar environment for C. burnetii. These findings demonstrate that, IFNγ-induced nutrient deprivation and altered intracellular niche can synergistically and effectively restrict lysosome-adapted pathogens.
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