Microfluidics without pumps: reinventing the T-sensor and H-filter in paper networks.

Conventional microfluidic devices typically require highly precise pumps or pneumatic control systems, which add considerable cost and the requirement for power. These restrictions have limited the adoption of microfluidic technologies for point-of-care applications. Paper networks provide an extremely low-cost and pumpless alternative to conventional microfluidic devices by generating fluid transport through capillarity. We revisit well-known microfluidic devices for hydrodynamic focusing, sized-based extraction of molecules from complex mixtures, micromixing, and dilution, and demonstrate that paper-based devices can replace their expensive conventional microfluidic counterparts.

Laboratory-scale protein striping system for patterning biomolecules onto paper-based immunochromatographic test strips.

A method for patterning narrow lines of biomolecules onto nitrocellulose membranes using laboratory syringe pumps is described. One syringe pump is used to drive the biomolecule solution through a needle, while another modified syringe pump acts as a one-dimensional translation stage, moving the needle across the membrane much like a pen. This method consumes very small volumes of reagents, and is a viable option for laboratory-scale fabrication and prototyping of point-of-care rapid diagnostic test strips.

Enabling a microfluidic immunoassay for the developing world by integration of on-card dry reagent storage.

As part of an effort to create a point-of-care diagnostic system for the developing world, we present a microfluidic flow-through membrane immunoassay with on-card dry reagent storage. By preserving reagent function, the storage and reconstitution of anhydrous reagents enables the devices to remain viable in challenging, unregulated environmental conditions. The assay takes place on a disposable laminate card containing both a porous membrane patterned with capture molecules and a fibrous pad containing an anhydrous analyte label. To conduct the assay, the card is placed in an external pumping and imaging instrument capable of delivering sample and rehydrated reagent to the assay membrane at controlled flow rates to generate quantitative results. Using the malarial antigen Plasmodium falciparum histidine-rich protein II (PfHRP2) as a model, we demonstrate selection of dry storage conditions, characterization of reagent rehydration, and execution of an automated on-card assay. Gold-antibody conjugates dried in a variety of sugar matrices were shown to retain 80-96% of their activity after 60 days of storage at elevated temperatures, and the release profile of the reconstituted reagent was characterized under flow in microfluidic channels. The system gave a detection limit in the sub-nanomolar range in under nine minutes, showing the potential to expand into quantitative, multi-analyte analysis of human blood samples.