The D4 Assay

Modern clinical medicine relies heavily on the blood-based diagnostic tests that measure the amount of protein biomarkers present in circulation to make clinical decisions. In hospital settings, this is most commonly done by enzyme-linked immunosorbent assay (ELISA). While accurate and sensitive, ELISA requires considerable resources, infrastructure, and expertise to perform. The D4 assay is a miniaturized, self-contained assay that can measure protein biomarkers in blood with ELISA-like performance without the need for equipment other than a smartphone and can be performed with minimal user training. Assay reagents are inkjet printed onto a glass chip coated with a special “zero-background” polymer coating, which acts to minimize biomolecular noise (making the assay very sensitive) and stabilize the reagents even without refrigeration. The assay is user-friendly because adding a liquid sample (blood, serum, cell lysate) to D4 chips automatically drives the assay to completion. Furthermore, the assay is very portable since a cellphone-based detector utilizes the phone’s camera lens to readout the fluorescence on the D4 assay. For a more in-depth explanation of how the D4 system works, read Joh, D.Y., et al. Because of the EpiView-D4 system’s portability, it has huge implications for healthcare in low-resource settings like Liberia.

Over the summer, I’m helping with two D4 assay projects. The first project is developing a point of care test for breast cancer. I’m optimizing a D4 assay that detects HER2, a protein found on breast cancer cells; this protein is important because if breast cancers are found to be HER2-positive, then they are likely to respond to so-called “anti-HER2” cancer drugs (e.g. trastuzumab), which is potentially life-saving. In the long-term, my goal is to make a multiplexed assay that targets the four major clinically-relevant biomarkers for breast cancer: these are ER, PR, HER2, and Ki67. This capability is standard care in the United States, but unavailable in many developing countries (where the majority of breast cancer deaths now occur). By having a single, low-cost, and user-friendly assay that profiles all four markers simultaneously, clinicians in the developing world will be able to match different breast tumors to the medications which they are most likely to respond to. The second project is developing a point-of-care test that rapidly identifies Methicillin-resistant Staphylococcus aureus (MRSA). MRSA can resist antibiotics due to expression of an altered penicillin-binding protein, PBP2a. Current methods for identifying MRSA versus methicillin-sensitive strains are based on culturing the bacteria, and this typically requires at least a day or longer.  If a point of care D4 assay can be developed to detect PBP2a, MRSA diagnosis and treatment could become more efficient.

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