A.S. Johnston, Y. Tang, M.M. Alam
Keywords: lab-on-a-chip diagnostics, Alzheimer’s disease (AD), microelectonic biosensor, single-walled carbon nanotubes (CNTs), dementia, biomarkers, amyloid-β, Tau, p-Tau, point-of-care
Summary:We designed and developed a lab-on-a-chip for the early diagnosis of Alzheimer’s Disease (AD) based on our patent-pending innovative nanotechnology by utilizing patterned microelectronic sensor devices for detecting Food and Drug Administration (FDA)-approved AD biomarkers (Amyloid-β 1-42, Tau, and p-Tau).(1) AD is a severe and complex neurodegenerative disorder characterized by forms of dementia and cognitive decline. The cost of AD patient care in the United States was estimated to be $259 billion for 2017, and estimated to reach $1.1 trillion by 2050.(2) The standard method of AD diagnosis involves a combination of imaging and cognitive tests, while definitive diagnosis is performed postmortem. Most of these tests are expensive, time-consuming, require highly-skilled personnel, and not used as a tool for point-of-care applications. Because AD onset can occur decades before the manifestation of pathological hallmarks, (3,4) a panel of biomarkers that can tap into this early window of opportunity will be beneficial in detecting, staging, treating, and monitoring the disease. Technology of microelectronic devices (MEDs) involves the site-specific deposition of highly sensitive and robust single-walled carbon nanotubes (CNTs), which serves a simple, rapid, and low-cost AD diagnostic tool in a point-of-care or clinical setting. CNT-based devices can attain high levels of sensitivity due to a relatively large surface area and allow for a wide range of conjugation and functionalization opportunities to obtain optimal sensing capabilities. We fabricated MED-based biosensors using following steps: (1) CNT incorporation using a dielectrophoretic deposition method, (2) AD-specific antibody conjugation followed by surface passivation to prevent non-specific binding, and (3) sensor characterization by current-voltage measurements. Our studies showed that the MEDs detected Amyloid-β 1-42, Tau, and p-Tau biomarkers with high sensitivity (concentrations as low as 10fM–50fM up to 100nM) in 1X PBS, artificially-spiked cerebrospinal fluid (aCSF), and clinical cerebrospinal fluid (CSF) media. In PBS, the MEDs revealed a sensor response ≈ 55% for Amyloid-β 1-42, 60% for Tau, and 50% for p-Tau. General responses in aCSF ranged from 40–60%, while responses for Tau and p-Tau in CSF showed slightly lower values (26–31%) due to possible unknown contents in the samples. Furthermore, we were able to distinctively distinguish responses between appropriate antibody-antigen pairs with that of controls as well as cross reactivity pairs. This data along with further results will be presented at the upcoming conference. We would like to thank our collaborators, Dr. Charles Glabe of UCI and Dr. John Ringman of USC for their support on this project. We also thank the NIH-National Institute of Aging (NIA)-Small Business Innovation Research (SBIR) Grant # 2R44AG046059-02A1. References: (1) M.M. Alam, U. Sampathkumaran. Modular Chemiresistive Sensor. 2015, U.S. Pat. Application 14/658,034 (approved); (2) Alzheimer’s Association. 2017 Alzheimer’s Disease Facts and Figures. https://www.alz.org/facts/overview.asp; accessed December 2017; (3) C. Humpel. Identifying and Validating Biomarkers for Alzheimer’s Disease. 2011. Trends in Biotechnology. 29(1):26–32; (4) B.X. Wong, Y.H. Hung, A.I. Bush, J.A. Duce. Metals and Cholesterol: Two Sides of the Same Coin in Alzheimer’s Disease Pathology. 2014. Frontiers in Aging Neuroscience. 6(91):1–17.