Effect of Surfactant Type and Redox Polymer Type on Single-Walled Carbon Nanotube Modified Electrodes

Abstract

Electrodes modified with single-walled carbon nanotubes (SWNTs) offer a number of attractive properties for developing novel electrochemical sensors. A common method to immobilize SWNTs onto the electrode surface is by placing a droplet of a SWNT suspension onto the electrode surface and allowing the solvent to evaporate. In order to maximize the properties of individual SWNTs, surfactants are normally present in these suspensions to provide stable and homogeneous SWNT dispersions. In this study we investigated the effect of different surfactants on the electrochemical and enzymatic performance of SWNT modified glassy carbon electrodes (GCEs). Amperometic biosensors for glucose were fabricated by a two-step procedure. In the first step, SWNT films were deposited onto GCEs by solution casting suspensions of SWNTs in water, Triton X-100, Tween 20, sodium cholate or sodium dodecylbenzenesulfonate (NaDDBS). In the second step, hydrogels containing a redox polymer and the enzyme, glucose oxidase (GOX), were deposited and cross-linked onto the SWNT-modified GCE. Three different redox polymers were tested: 3-ferrocenylpropyl-modified LPEI, (Fc-C3-LPEI), 6-ferrocenylhexyl-modified LPEI, (Fc-C6-LPEI), and poly[(vinylpyridine)Os(bipyridyl)2Cl](2+/3+)(PVP-Os). Biosensors constructed with SWNT films from suspensions of Triton X-100 or Tween 20 generally produced the highest electrochemical and enzymatic responses, with Triton X-100 films producing current densities of ~1.7-2.1 mA/cm(2) for the three different redox polymers. In contrast, biosensors constructed with SWNT films from sodium cholate suspensions resulted in significant decreases in the electrochemical and enzymatic response and in some cases showed no enzymatic activity. The results with SWNT films from NaDDBS suspensions were dependent upon the specific redox polymer used, but in general gave reduced enzymatic responses (~0.05-0.4 mA/cm(2)). These results demonstrate the importance of surfactant type in fabricating SWNT-modified electrode films.

Development of Fructose Dehydrogenase-Ferrocene Redox Polymer Films for Biofuel Cell Anodes

“…The increase in the current response is most likely related to both an increase in the electrochemical surface area provided by the SWNTs and more of the redox polymer's ferrocene centers being electrochemically accessible. 32,33 The large shift in the peak separation potentials is in consistent with our previous reports. 32,33 The cause of the change in the oxidation and reduction potentials is unknown and may be related to differences in the ability of SWNTs to donate or accept electrons at (i) the glassy carbon interface, (ii) junctions between interconnected SWNTs, or (iii) with ferrocene redox centers.…”

“…32,33 The large shift in the peak separation potentials is in consistent with our previous reports. 32,33 The cause of the change in the oxidation and reduction potentials is unknown and may be related to differences in the ability of SWNTs to donate or accept electrons at (i) the glassy carbon interface, (ii) junctions between interconnected SWNTs, or (iii) with ferrocene redox centers. Similar to the electrochemical results, modification of the GCEs with the SWNT films had a significant effect on the enzymatic response to fructose.…”

“…The redox polymers PVP-Os 31 and Fc-C 6 -LPEI 30 were prepared as previously described. Dispersions of SWNTs were prepared as previously described 33 by adding 2 or 5 mg of SWNT powder to 5 mL of a Triton X-100 aqueous solution resulting in a final SWNT concentration of 0.4 and 1.0 mg/mL, respectively. The concentration of Triton X-100 in the aqueous solution was 5 g/L.…”

“…33 To form the SWNT film, 10 μL of the Triton X-100/SWNTs dispersion was cast on top of a polished glassy carbon electrode and allowed to dry overnight at room temperature. Next a 3 μL aliquot of the Fc-C 6 -LPEI/FDH/EGDGE mixture described above was deposited on top of the SWNTs film and allowed to dry and crosslink overnight ( Figure 1).…”

Electrochemical Behavior and Analytical Applications of Electronically Type-Sorted Carbon Nanotube Electrode

“…No negative factors from the surfactant, such as the hydrophobic naphthenic groups of the sodium cholate surfactant blocking the electronic signal, (22) were observed. Figure 2 shows CV profiles for the electrodes with unsorted SWCNTs, m-SWCNTs, and s-SWCNTs.…”