Chemically Functionalized Carbon Nanotube Label for Immunoassay
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Chemically Functionalized Carbon Nanotube Label for Immunoassay Adeyabeba Abera1 and Jin-Woo Choi1, 2 1 Department of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, LA 70803, USA 2 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70803, USA ABSTRACT A recent approach in disease diagnosis and viral epidemics is aimed at point-of-care tests that could be administered near the patient rather than time-consuming processes involving centralized laboratories. Point-of-care devices provide rapid results in simple and low-cost manner requiring only small sample volumes. These devices will strongly benefit from advanced materials and fabrication methods to improve their efficiency and sensitivity. We report a functionalized carbon nanotube label for an immunosensor application. Carbon nanotube label was prepared by modifying the carbon nanotube surface to anchor biomolecules. First, the carboxylic acid treated multi-walled carbon nanotubes (MWCNTs) were uniformly dispersed with polyvinylpyrrolidone (PVP) by sonication in aqueous solution. PVP partially wraps around the carbon nanotubes and exposes the surface of the nanotubes for further functionalization. The MWCNTs were then conjugated with human immunoglobulin G (IgG) using EDC/Sulfo-NHS coupling chemistry, where the antibodies occupied sites not covered by PVP. The dispersion, surfactant modification, and antibody conjugation of the MWCNTs were also confirmed using SEM and TEM images. The successful functionalization of the MWCNTs and reactivity of the covalent attached antibodies were demonstrated for specific antigen binding on the microelectrode device. The carbon nanotube-based detection mechanism could be tailored for screening various analyte specific molecules. Furthermore, the reported technique could easily be integrated in various microfluidic and lab-on-a-chip devices for the development of functional electronic sensors providing quantitative, sensitive, and low-cost detection in pointof-care setup. INTRODUCTION A major concern in practical use of carbon nanotubes (CNTs) is their poor solubility in aqueous solution due to the strong van deer Waals attraction between carbon nanotubes [1-3]. Surface modification of carbon nanotubes is necessary to enhance the solubility and to form functional groups for immobilizing biomolecules. Adsorption of surfactants or polymers on the surface of carbon nanotubes is known to be an effective approach to disperse CNTs in aqueous solution [4-6]. Among various surfactants to enhance carbon nanotube dispersion, polyvinylpyrrolidone [7] and poly(ethylene glycol) [8] have been widely studied. It has also been reported that thin layer of surfactant or polymer coating on CNTs do not cause significant change in the electrical conducting properties.
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For potential immunosensing applications, the surface of the CNTs needs to be functionalized with functional groups for the immobilization of proteins through stable covalent bonding [9]. Functional groups ar
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