Abstract
Vertically aligned single-walled carbon nanotube (VASWCNT) assemblies are generated on cysteamine and 2-mercaptoethanol (2-ME)-functionalized gold surfaces through amide bond formation between carboxylic groups generated at the end of acid-shortened single-walled carbon nanotubes (SWCNTs) and amine groups present on the gold surfaces. Atomic force microscopy (AFM) imaging confirms the vertical alignment mode of SWCNT attachment through significant changes in surface roughness compared to bare gold surfaces and the lack of any horizontally aligned SWCNTs present. These SWCNT assemblies are further modified with an amine-terminated single-stranded probe-DNA. Subsequent hybridization of the surface-bound probe-DNA in the presence of complementary strands in solution is followed using impedance measurements in the presence of Fe(CN)63−/4− as the redox probe in solution, which show changes in the interfacial electrochemical properties, specifically the charge-transfer resistance, due to hybridization. In addition, hybridization of the probe-DNA is also compared when it is attached directly to the gold surfaces without any intermediary SWCNTs. Contrary to our expectations, impedance measurements show a decrease in charge-transfer resistance with time due to hybridization with 300 nM complementary DNA in solution with the probe-DNA attached to SWCNTs. In contrast, an increase in charge-transfer resistance is observed with time during hybridization when the probe-DNA is attached directly to the gold surfaces. The decrease in charge-transfer resistance during hybridization in the presence of VASWCNTs indicates an enhancement in the electron transfer process of the redox probe at the VASWCNT-modified electrode. The results suggest that VASWCNTs are acting as mediators of electron transfer, which facilitate the charge transfer of the redox probe at the electrode–solution interface.
Highlights
Significant progress has been made over the last few years to generate vertically aligned single-walled carbon nanotube (VASWCNT) arrays on various surfaces due to their potential applications in nanoscale circuits [1]; ultrathin, flexible, and transparent conductors [2]; super-capacitors [3]; and, in particular, novel biosensors [4, 5]
VASWCNTs on the amine-terminated gold surface are created using a self-assembled monolayer of aminothiol
In summary, VASWCNT arrays have been generated on gold surfaces and have shown significant changes in surface roughness compared to bare gold surfaces
Summary
Significant progress has been made over the last few years to generate vertically aligned single-walled carbon nanotube (VASWCNT) arrays on various surfaces due to their potential applications in nanoscale circuits [1]; ultrathin, flexible, and transparent conductors [2]; super-capacitors [3]; and, in particular, novel biosensors [4, 5]. VASWCNT arrays generated by self-assembly techniques are attractive because of the low-temperature wet-chemical approach Due to their range of electrical conductivities, excellent chemical stability, high surface area, and tubular structure, VASWCNTs have attracted much attention in order to achieve high sensitivity and detection limits in electrochemical biosensors [8]. This has been exemplified in a number of recent studies on the advantages of facile electron transfer properties of VASWCNTs compared to randomly distributed, disordered SWCNT mats on electrode surfaces [8,9,10,11,12]. In addition to the limited number of reports on post-synthesis assembly, the electrochemistry of these systems is not yet fully
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