Development of carbon nanotube based biosensor fabrication for medical diagnostics application

Abstract

Carbon nanotubes are tiny hollow cylinders, made from a single grapheme sheet, that possess many amazing properties. Spurred by the Human Genome Project, deoxyribonucleic acid (DNA), carbon nanotube based biosensors are indispensable tools in molecular biology. A biosensor is an analytical device which converts a biological response into an electrical signal. A SWNT can be metallic, semiconducting, or semimetallic, depending on its chirality. Carbon materials have been used as components in biosensors for over a decade. Carbon nanotubes (CNT) chemical functionalization can be used to attach almost any desired chemical species to them, which allows us for instance to enhance the solubility and biocompatibility of the tubes. This has permitted the realization of composite electrodes comprising CNTs well-dispersed in an appropriate polymer matrix. DNA hybridization biosensors offer considerable promise for obtaining sequence-specific information in a faster, simpler and cheaper manner compared to traditional hybridization assays. These technologies rely on the immobilization of a single-stranded DNA probe onto different physicochemical transducers that convert the hybridization event into an electrical or optical signal. Applications for this technology are numerous and far reaching, including identification of pathogens, gene expression monitoring, diagnosis of genetic disorders and forensic examination. In this project, carbon nanotube based biosensor was fabricated on p-type silicon wafer which was coated with 100 Å -200 Å of silicon dioxide, titanium 100 Å-200 Å were grown and followed with 900 Å-1000 Å of Aurum.This metal multilayer is used for interconnections and reacts as conduction element for biosensor based carbon nanotube device. Silicon dioxide with the thickness of 300 Å-400 Å was grown once again, titanium of 100 Å-200 Å thick was grown and followed w- - ith 900 Å-1000 Å of Aurum. The distance between these two electrodes is 3-4 μm. Carbon nanotubes were deposited using dielectrophoresis and nanomanipulation method. The diameter of SWNT was around 1.2nm -1.5 nm. Small amount of SWNTs were ultrasonically dispersed in an aqueous solution for 30 minutes,then a small drop was casted the wafers in between the pairs of metal multilayer electrodes.AC bias was applied and the peak-to-peak AC voltage was between 4 and 8 V, and the frequency was fixed at 10 MHz to 50 MHz. Once the resistance drop was detected, the AC bias was turned off immediately. To improve the integration between the SWNTs and electrodes, this device was also annealed at 300°C for 15 minutes. AFM nanomanipulation takes place to ensure the placements of all SWNTs were successful. Nitride was grown to form a test channel for electrical and final testing. In this project development, we provide an introduction to biosensors based on carbon nanotubes. These carbon nanotube electrodes have very high sensitivity to detect biomolecules. For decades, the manipulation and placement of carbon nanotubes has always been research thoroughly. Dielectrophoresis and nanomanipulation method has been applied on this project because it has really big advantage over random spin coating and direct growth of carbon nanotubes. This project is currently in progress on integration of carbon nanotube and the procedure to apply the DNA onto the device using deoxyribonucleic acid (DNA) hybridization process.