Cheap and portable virus detection is extremely important for the future progress of accessible health diagnostics. Norovirus, the virus featured in our recent publication, is tricky to detect because just a few tens of virus particles can lead to the infection of a human. This virus was one of the original cruise-ship dangers, similar to the issues we saw with SARS-CoV-2 in early 2020.

In addition to being infectious at low doses, virus diagnostics can be a time consuming, expensive, and highly technical process. Our lab has spent many years figuring out ways to optimize the chemistry and lower the cost of the assay, all the while trying to keep our sensitivities and specificities competitive with existing techniques, such as ELISA and RT-PCR (virus culture is not an option as norovirus is not culturable in conventional lab settings).

The protocol presented in this paper is a collection of everything we have learned along the journey of portable norovirus detection using paper-based microfluidics, a smartphone-fluorescence microscope, and particle-based immunoassay. We use a 3D-printed enclosure to house the microfluidic chip, a cheap microscope attachment, and the appropriate LEDs and optical filters to illuminate the fluorescent particles. The smartphone photographs any clumps of particles to be analyzed and quantified. From optimizing the immunoassay sensitivity, choosing the materials and design of the wax-printed microfluidic chip, 3D-printing an enclosure, and pushing the smartphone camera to its limits with image processing code, this project encourages us to find connections across the definition of the STEM field to achieve our goal of low-cost, portable, norovirus diagnostics.

Today, we are continuing this research to adapt it for detection of SARS-CoV-2 from human mouth gargle samples at the University of Arizona. We hope that any readers interested in the protocol can learn from our triumphs and failures with norovirus to jump forward and continue progressing the technique for detection of other pathogens or chemicals. We are on the path to a future where basic health diagnostics can be accessible whether you are in the lab, out in the field, or at a small clinic.

Read our recent publication in Nature Protocols to learn more about this project: Norovirus detection in water samples at the single virus copies per microliter using a smartphone-based fluorescence microscope