Cheap Paper Strips Developed for Disease Diagnostics

In addition, a new touch paper spray method was developed for on-chip, sensitive, and cost-effective analyte detection.

Instead of regular ink, the scientists used wax ink to trace the outline of channels and reservoirs on the paper. The wax penetrates the paper and forms a waterproof barrier to capture the blood sample and keep it between layers. One 8.5 × 11-inch sheet of paper can hold dozens of individual tests that can then be cut apart into strips, each a little larger than a postage stamp. The technology works differently than other paper-based medical diagnostics like home pregnancy tests, which are coated with enzymes or gold nanoparticles to make the paper change color. Instead, the paper contains small synthetic chemical probes that carry a positive charge. It's these "ionic" probes that allow ultra-sensitive detection by a handheld mass spectrometer.

The chemists designed ionic probes to tag specific antibodies that extract the disease biomarker from the blood and onto the paper chip. Once they are extracted, the chemicals stay unchanged until the paper is dipped in an ammonia solution at the laboratory. There, an individual peels the paper layers apart and holds them in front of a mass spectrometer, which detects the presence of the probes based on their atomic characteristics, and, by extension, the presence of biomarkers in an infected person's blood.

The method successfully demonstrated the detection of Plasmodium falciparum histidine-rich protein 2 antigen and multiplexed and simultaneous detection of cancer antigen 125, a protein biomarker for ovarian cancer and carcinoembryonic antigen, a marker for cancer of the large intestine, among other cancers. The the strips were stored away and re-tested every few days to see if the signal detected by the mass spectrometer would fade over time, which it did not. The signal was just as strong after 30 days as on day one, meaning that the disease proteins were stable and detectable even after a month. The study was published on May 9, 2016, in the Journal of the American Chemical Society.

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