Nanotextured Electrical Immunoassays for Ultrasensitive Protein Detection
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Nanotextured Electrical Immunoassays for Ultrasensitive Protein Detection Timothy O. Mertz1, Krishna Vattipalli1, Tom Barrett2, John Carruthers3 and Shalini Prasad1 1 Department of Electrical Engineering and Computer Science, Wichita State University, Wichita, Kansas 67260, U.S.A. 2 Department of Medicine, Oregon Health and Sciences University, Portland, Oregon 97239, U.S.A. 3 Department of Physics, Portland State University, Portland, Oregon 97201, U.S.A. ABSTRACT This paper describes the development of nanomonitors, which are electrical immunoassays for detection of multiple protein biomarkers. These devices are hybrid sensors with micro-fabricated electrode arrays on a silicon substrate, and integrated nanoporous alumina membranes to provide protein confinement and signal amplification. The disease biomarkers Creactive protein and Myeloperoxidase have been detected by the nanomonitors in ultra-low concentrations. Proteins were detected in pure samples, human serum, and patient blood samples. The detection accuracy and sensitivity of the nanomonitors in patient samples was comparable to the Enzyme Linked Immunosorbent Assay (ELISA) method of protein detection. Nanomonitors provide the additional benefits of being rapid, label-free, sensitive, and cost effective, providing improvements over traditional protein detection methods, and having potential applications in disease diagnosis. INTRODUCTION Robust diagnosis of a disease can be accomplished by reliable detection of multiple proteins that are identified as disease biomarkers. Traditional assay methods for protein detection such as enzyme-linked immunosorbant assay (ELISA) have several limitations – need for use of labels, time of detection in the order of hours, large volume of reagents, high cost of assay, potential for denaturing of the proteins, and multiple proteins cannot be detected simultaneously due to the complexity of the assay [2]. Research is focused on developing a more effective alternative to traditional assays. This paper discusses the design and development of nanomonitors, which are electrical immunoassays for label-free, sensitive, fast, reliable and cost effective detection of multiple protein biomarkers. These nanomonitors are comprised of a base silicon substrate with microfabricated planar microelectrode arrays onto which a nanomaterial is integrated. This creates a nanotextured surface to enable protein binding, and the electrical charge associated with this binding can be measured. The nanomonitors operate on the principle that conjugation of proteins results in a charge perturbation in the electrical double layer at the interface between the biomolecule and the measurement site, thus causing a measurable change in the capacitance. The integration of the electrically insulating nanoporous alumina membranes with the device results in isolated nanoscale well-like structures, also known as nanowells, which exhibit size matching with respect to proteins. The large surface area to volume ratio increases binding of target molecules. Size matc
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