Researchers developed a COVID-19 testing method that uses a smartphone microscope to analyze saliva samples and deliver results in about 10 minutes. The method combines the speed of existing nasal swab antigen tests with the high accuracy of nasal swab PCR (polymerase chain reaction) tests. They are adapting an inexpensive method that they originally created to detect norovirus — the microbe famous for spreading on cruise ships — using a smartphone microscope. They plan to use the method in conjunction with a previously developed saline swish-gargle test.

Traditional methods for detection of norovirus or other pathogens are often expensive, involve a large suite of laboratory equipment, or require scientific expertise. The smartphone-based norovirus test consists of a smartphone, a simple microscope, and a piece of microfluidic paper — a wax-coated paper that guides the liquid sample to flow through specific channels. It is smaller and cheaper than other tests, with the components costing about $45.

The basis of the technology is relatively simple. Users introduce antibodies with fluorescent beads to a potentially contaminated water sample. If enough particles of the pathogen are present in the sample, several antibodies attach to each pathogen particle. Under a microscope, the pathogen particles show up as little clumps of fluorescent beads, which the user can then count. The process — adding beads to the sample, soaking a piece of paper in the sample, then taking a smartphone photograph of it under a microscope and counting the beads — takes about 10 to 15 minutes. A non-scientist could learn how to do it by watching a brief video.

The team created a 3D-printed housing for the microscope attachment and microfluidic paper chip as well as a method called adaptive thresholding. Previously, researchers set a fixed value for what quantity of pathogen constituted a danger, which limited precision levels. This method uses artificial intelligence to set the danger threshold and account for environmental differences, such as the type of smartphone and the quality of the paper.

The team is working on an even simpler method that leaves slightly more room for error. It involves the same technology but instead of a smartphone microscope and specially designed enclosure, users would only need to download a smartphone app and use a microfluidic chip stamped with a QR code.

Unlike the fluorescent microscope technique, where the chip must be in just the right position, the user simply takes a snapshot of the chip. Regardless of the angle or distance the photo is taken from, the smartphone app can use AI and the QR code to account for variances and run calculations accordingly.

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