Biological Functionalization of Carbon Nanotubes
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BIOLOGICAL FUNCTIONALIZATION OF CARBON NANOTUBES Ranjani Sirdeshmukh, Kasif Teker and Balaji Panchapakesan Delaware MEMS and Nanotechnology Laboratory Department of Electrical and Computer Engineering University of Delaware, Newark, DE 19716 ABSTRACT Carbon nanotubes are known for their exceptional mechanical and unique electronic properties. The size dependant properties of nanomaterials have made them attractive to develop highly sensitive sensors and detection systems. This is especially true in biological sciences, where the efficiency of detection systems reflect on the size of the detector and the sample required for detection. At approximately 1.5 to 10nm wide, and approximately 1.5 to 2µm long, the use of carbon nanotubes as sensors in biological systems would greatly increase the sensitivity of detection and diagnostics, for a reduced sample size consisting of few individual proteins and antibodies. Since all the atoms in carbon nanotubes are surface atoms, binding proteins or antibodies to the surfaces can greatly affect their surface states, and thus their electrical and optical properties. This effect can be exploited as a basis for detecting biological surface reactions in a single protein or antibody attached to carbon nanotube surfaces. In this paper, we show the binding of fluorescently tagged antibodies in phosphate buffered saline on the surfaces of carbon nanotubes. Investigations using a confocal microscope suggest a significant interaction of the antibodies with the surfaces of the nanotubes, the intensity depending on incubation time. Since the surface area to volume ratio of CNTs is high, the use of surfactant to separate the nanotubes creates a greater surface area for antibody attachment. The interaction between CNTs and antibodies is seen to be primarily due to adsorptive surface phenomenon, between the nanotube sidewalls and antibody molecule clusters. INTRODUCTION Biological functionalization of nanomaterials has come to be of significant interest in recent years due to the possibility of developing sensitive and ultra-fast detection systems that can be addressed using electronic or optical techniques. Most often, biological sensing techniques depend on optical signals derived from the analytes in use, thus involving a series of steps for preparation, varying reagents to differentiate components, and a relatively large sample size. Although these techniques are relatively sensitive, they result in complex data analysis involving unnecessary time consumption and expensive examination techniques. Miniaturizing processes in biological sensing to make them application specific could result in lowering sample size, time and expenses related to detection and sensing. Nanostructures functionalized with biological assays could be the key to novel nano-biosensing techniques. Several issues are important regarding functionalization of biomaterials on solid-state nanomaterials such as biocompatibility, specificity to the target biomolecule, extent of functionalization, interface effects and
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