Origami-based Fast, Reconfigurable Flow Switch for Paper Microfluidics

Researchers have recently developed a new type of switch for paper microfluidics made out of folded chromatography paper, published in Lab on a Chip. The switch enables programmable switching of fluidic connections, and offers a number of advantages over current techniques. 

We spoke to Santosh Pandey, Associate Professor, Iowa State University, to learn more about the origami-based switch and its development.

What are some of the limitations of previously created switches for paper microfluidics?

Previous approaches of creating bidirectional switches for paper microfluidics have been limited by their long response time, the need for large volumes of actuation fluid, and the use of external components (such as magnetic timing valves and cellulose sponge) that increases the overall cost of the device.

Can you tell us more about the recently published origami-based switch? What led to its development?

There are several examples of one-way switches in paper microfluidics. However, real-world paper microfluidic applications can benefit from bidirectional switches that are fast and reconfigurable with minimal cost overhead. It was evident that the cheapest switch would be made of the same chromatography paper used to make flow channels but without adding extra components. The question was how we can actuate a strip of chromatography paper to connect or disconnect separate flow channels. We found that solution was simple: create a fold or crease in a paper strip, tape one end of it, and wet the crease with a small drop of water. During this process, a differential swelling occurs along the thickness of the paper causing the free end of the paper strip to rise up or lower by over 2 millimetres. This actuation mechanism can be exploited to realize a number of switching operations, as illustrated in the article and supporting movies.  

What are some of the advantages that the switch offers?

The response time is much reduced. The switch is activated within two seconds of wetting the crease of the paper strip. Only a small volume of water (four microliters) is required to actuate the switch. There are no extra components needed. Building the switch is very straightforward as the user simply creates a fold at a predefined distance from the flow channels and tapes one end of it. Multiple switches can be easily integrated next to each other.     



Which applications could this help to improve? 

We built an assay to simultaneously detect the presence of three analytes (glucose, protein, and nitrite) in artificial saliva. These switches may be particularly useful for applications where a sequence of chemical reactions occur in series, each with its characteristic time delay.      

Can you tell us about any future work you have planned?

We are exploring ways to scale down the physical size of the switches and to integrate them with existing paper microfluidic assays.  

Dr Pandey was speaking to Anna MacDonald, Editor for Technology Networks.

Reference:

Kong, T., Flanigan, S., Weinstein, M., Kalwa, U., Legner, C., & Pandey, S. (2017). A fast, reconfigurable flow switch for paper microfluidics based on selective wetting of folded paper actuator strips. Lab Chip. doi:10.1039/c7lc00620a