Self-Assembled Carbon Nanotube Electrode Arrays: Effect of Length of the Linker between Nanotubes and Electrode

Abstract

The influence of the length of the carbon chain of a self-assembled monolayer (SAM) on gold electrodes on the electrochemical performance of carbon nanotube arrays attached to the SAM was explored. Four electrode constructs were assessed, all of which were modified with four different lengths (C2−C11) of amine-terminated alkanethiols. The four constructs were gold electrodes modified (1) with SAMs alone, (2) with carbon nanotubes randomly dispersed onto the SAM-modified electrodes by drop coating, (3) with vertically aligned carbon nanotubes formed by self-assembly onto the SAMs, and (4) with vertically aligned nanotubes with ferrocene attached to the nanotubes. By use of ruthenium hexaammine as a redox probe, the attachment of the carbon nanotubes to the SAM, either randomly dispersed or aligned, enabled electrochemistry to be observed at SAMs that were passivating prior to attachment of the nanotubes. The electrochemistry decayed exponentially with methylene chain length as expected but with a surprisingly low attenuation factor (β value) for the nanotube-modified surfaces. For randomly dispersed nanotubes, the β value was 0.27 per -CH2- (s = 0.04, n = 4), and for the vertically aligned nanotubes, 0.66 per -CH2- (s = 0.04, n = 4). A similar β value of 0.62 per -CH2- for vertically aligned nanotubes with ferrocene attached provided good evidence that the results with ruthenium hexaammine were due to tunneling through the SAM rather than electrochemistry proceeding via defects in the SAM or the nanotubes penetrating the SAM to the underlying electrode.

Charge Transfer Within Multilayered Films of Gold Nanorods

“…This effect of the aliphatic chain thiol has been frequently observed at SAM modified electrodes (Chou et al, 2009;Su et al,2006). The sequential self-assembly of the AuNR 1 layer has determined a decrease of the charge transfer resistance by 3 orders of magnitude (n = 2, table 2).…”

“…The Faradaic process was highly hindered by the 1,6hexanedithiol layers ( Figure 5, n= 1, 3, 5, 7). This electrochemical behaviour is caused by the insulating properties of this dithiol when self-assembled on gold electrodes (Chirea et al, 2009(Chirea et al, , 2010Chou et al, 2009). For example, the first layer self-assembled on the gold electrodes determined a disappearance of the Faradaic currents in the cyclic and square wave voltammograms ( Figure 5, n = 1, black curve) as compared to the bare gold electrode ( Figure 5, n=0, dashed black curve) illustrating a dense packing of the 1,6hexanedithiol layer on the gold electrodes.…”

“…The difference between these two types of multilayers is in the nature of the interaction between the redox probes in solution and the outermost layers. The depressed semicircles observed in the EIS spectra of the 1,6HDT outermost layers are due to the insulating properties of the aliphatic chain of the dithiol which is blocking the electronic communication between the redox probes in solution and the underlying bare gold electrodes (Chou et al, 2009;Su et al,2006). Table 2.…”

Vertically Aligned Single‐Walled Carbon Nanotubes by Chemical Assembly – Methodology, Properties, and Applications

“…Among these two approaches, most of the researchers preferred to choose the amide bond as the linking bridge to fix the shortened SWNTs on substrates. [44,[46][47][48]50,[65][66][67][71][72][73][94][95][96][97][98][99][100] This is possibly due to the high stability of amide bond and the high efficiency of the condensation reaction between carboxylic and amino groups. Figure 5B shows the typical tapping mode AFM image of v-SWNTs prepared on gold substrates using surface condensation reaction.…”

Electrochemical Biosensing with Carbon Nanotubes

“…Diao and colleges Diao & Liu (2005) shown that the adsorbed SWCNTs act as many "electron relay stations" that mediate electrons between the metal electrode and redox centers. Also it is noted that the linking bonds at the ends of the tubes ensure an high electron transfer between nanotubes and surfaces Chidsey et al (1990);Cui, Primak, Zarate, Tomfohr, Sankey, Moore, Moore, Gust, Harris & Lindsay (2001);Cui et al (2002);Finklea & Hanshew (1992); Koehne et al (2004) but Gooding et al Chou et al (2009) reported that the electron-transfer rate at the nanotube-modified electrodes decayed exponentially with distance when the chain of the molecule bridge is increased. In this context our recent study on the combined effect on height and surface density of nanotubes give an overall point of view of HET dynamics in SWCNT forests Lamberti et al (2011).…”