Biomedical engineers at Duke University have created a portable diagnostic tool that can detect telltale markers of disease as accurately as the most sensitive tests on the market, while cutting the wait time for results from hours or even days to 15 minutes.

Created by inkjet-printing an array of antibodies onto a glass slide with a nonstick polymer coating, the diagnostic tool, called the D4 assay, is a self-contained test that can detect low levels of antigens, the protein markers of a disease, from a single drop of blood.

By creating a sensitive, easy-to-use ‘lab on a chip,’ the researchers plan to bring rapid diagnostic testing to areas that lack access to standard lab-based diagnostic technologies.

The platform is described in the Proceedings of the National Academy of Sciences.

Beyond detecting diseases, healthcare workers use diagnostic tools to assess the severity of an illness, plan an effective treatment strategy, and track an individual’s response to treatment. While some tests, like the lateral flow test, are fast, portable and easy to use, they aren’t usually sensitive enough to provide information beyond the presence or absence of a particular biomarker, so healthcare workers often need to use quantitative methods to determine how severe an infection is.

Currently, the gold standard for quantitative diagnostic tests is the enzyme-linked immunosorbent assay (ELISA), which identifies how many specific antigens are present in a biological sample. While ELISA is among the most sensitive immunoassay tools on the market for detecting diseases like Zika and HIV or tracking hormone levels in the blood, it requires trained researchers or liquid handling robotic devices to follow a series of time-consuming steps to ensure that no unwanted proteins stick to the assay and muddy the results. The test also requires bulky laboratory instruments for data analysis, making it ill-equipped for use in resource-limited settings.

As an added complication, the ELISA platform can take up to 24 hours to show test results –which often means a delay in treatment even as the disease continues to spread.

The D4 assay allows clinicians to avoid these problems without sacrificing sensitivity or accuracy. The new assay can identify a disease biomarker in as few as 15 minutes, and results can be read using a tabletop scanner or 3D printed smartphone attachment that uses the phone’s camera to read the results, enabling the tool to be used in point-of-care settings for rapid diagnosis.

The real significance of the assay is the polymer brush coating,’ commented Ashutosh Chilkoti, Chair of the Department of Biomedical Engineering (BME) at Duke and senior author on the paper.

The polymer brush allowed us to store all of the tools we need on the chip while maintaining a simple design.’

Using the D4 assay, researchers don’t need to follow a complicated workflow to clear non-target proteins from their slide, as with the ELISA test. Instead, they simply need to wash the slide in a buffer solution to remove any extraneous particles.

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