A New Wet Chemical Self Assembling Approach to Immobilize Single-Walled carbon Nanotubes (SWCNTs)On Gold Substrate

Abstract

The advent of green chemistry in the last two decade has significantly altered the science and technology of materials. For example, silicon (Si) is known to be the key material for electronic devices such as television, mobile phones, computers, most of which have enriched the quality of life tremendously. However, Si does not interfere with nature, which mostly relies on oxygen, nitrogen, carbon and few other elements and radicals. Since the bench-mark discovery of Carbon Nanotube (CNT) by Iijima at 1991, it makes a milestone in Nano-Tech research field, which can replace Si and can lead to better electronic devices than those from Si, great excitement ensued [1]. Incidentally, carbon has another close companionship with silicon; it is just above Si in group IV B of elements in the periodic table. The scientists paid passable attention on the application of CNT because of its solitary structure, high mechanical strength, chiralitydependent conductivity etc. These unique properties of CNT make it a good aspirant for nanoelectronic devices, electron field emission sensors [2], scanning probes, chemical sensors [3], Nanotube actuators [4] and so on. Due to very high aspect ratio, tangled nature and lack of specific functionality, unmodified CNT has hardly little practical interest to researchers. Due to strong intertube Van der Waals interaction, CNTs are normally insoluble in many solvents. Therefore, strategic approaches toward the solubilization of CNTs by debundling are important for the application of CNTs. Modified CNTs with comparatively shorter length in the range of 2 μm, can act as molecular electronic devices which provide as connectors. Couple of intriguing researches have been reported [5-10] to organize randomly tangled CNTs into well arrayed patterned on gold surface by condensation agent, dicyclohexyl-carbadiimide (DCC) and surface active agent, N,Ndimethylformamide (DMF). Especially scientists are interested to develop wet chemical approach to immobilize SWNTs on solid surface, because successful patterned, well aligned short SWNT arrays can act as nanoelectrodes that can swap electrons between a conductive substrate and redox couple in solution [6]. Gooding et al. and willner and coworker [11] showed that immobilized SWNTs on gold electrode can be pay roll as nanowires, which allow electron communication between the underlying electrode and electro active proteins chemically bonded on SWNTs. Liu et al. reported the electrochemical behavior of AU/AUT/SWCNT electrodes using an electron transfer mechanism which encompass an electron tunneling process across the AUT (11-amino-n-undecanthiol) monolayer [8]. These studies insinuate that, immobilized SWNTs into conductive solid surfaces have substantial potential for electrochemical sensors, bioelectronics devices, solar cells, acoustic and optical sensors [12, 13]. In this study, I have reported an alternative strategy for immobilizingrandomly, comparatively shortened SWNTs on gold surface. Here, the carboxyl SWNTs are immobilized on thiol modified amino treated gold surface via wet chemical approach with the aid of linker N-(3- Dimethylaminopropyl)-N′-ethylcarbidiimide hydrochloride (EDC HCL) and N-hydrosulfosuccinimide (Sulfo-NHS). The performance of immobilization of SWCNT was evaluated by SEM, AFM, optical and Raman Spectroscopy. This approach enables the formation of SWCNT monolayer on gold substrate and turns the hydrophobic gold substrate into hydrophilic SWCNT patterned gold surface. A gold patterned surface on Silicon wafer has been fabricated by Photolithography technique to check the feasibility of immobilization on patterned surface. The main reason to come up with different approach is, to increase the efficiency of the process. The existing conventional method has several limitations including temperature effect, poor efficiency and health hazards. We believe that, properly patterned densely arrayed SWNTs on gold will be a potential candidate for capacitive sensor and bio-sensor field.