Carbon nanotube based biosensor for high sensitivity and dual mode measurement

Abstract

We have fabricated carbon nanotube (CNT)-based biosensors on transparent quartz substrates, which can detect biomolecules by measuring the conductance change and the surface plasmon resonance (SPR). The device has a metal semiconductor field effect transistor (MESFET) structure with a metal (Au) top gate between source and drain electrodes. Since this Au topgate acts as a Schottky metal gate, the conductance of the device is controlled by the metal gate. In order to see whether it is possible to detect biomolecules adsorbed on the Au topgate using the CNT-MESFET, thiol-modified single strand DNA molecules are immobilized on the Au top gate and then DNA molecules with the complementary base sequence are added. When DNA hybridization occurs, the CNT conductance is observed to decrease, suggesting that biomolecules adsorbed on the Au top gate can be detected by measuring the conductance change. In addition, the Au top gate is also able to be utilized for SPR measurements, which detects the change in refractive index induced by binding of biomolecules on the metal surface. Indeed, we have demonstrated that DNA hybridization can be detected using the CNT-MESFET by measuring the SPR angle shift. Since the sensitivity of biosensors measuring the conductance change is higher than SPR biosensors, whereas the reproducibility and the reliability are better in SPR biosensors. Therefore, this dual mode CNT biosensor is expected to provide high sensitivity reinforced with more reliability. We compared the sensitivity of CNT-MESFET sensor and CNT-FET sensor using measuring the electrical conductance. CNT-MESFET showed higher sensitivity than the CNT-FET sensor due to the high gate capacitance in aqueous environment and the merit of immobilization biomolecules at Au surface.