Metal-Mediated Electrochemical Oxidation of DNA-Wrapped Carbon Nanotubes

Interplay of proton and electron transfer to determine concerted behavior in the proton-coupled electron transfer of glutathione oxidation

Glutathione (GSH), whose thiol group dictates its redox chemistry, is oxidized to the thiyl radical (GS˙), which rapidly dimerizes to GSSG. Previously, we found that the oxidation rate of GSH by IrCl62- depends on the base (B) concentration and the pKa of its conjugate acid BH+, so that collateral to a stepwise mechanism, the concerted pathway GSH + IrCl62- + B = GS˙ + IrCl63- + BH+ was proposed as the rate determining step. Herein, this investigation is extended to include oxidant-base pairs that render exothermic and endothermic conditions of ΔG°' for electron transfer (ET) and proton transfer (PT). Experiments were conducted by the reaction of GSH with an electrogenerated oxidant M+ and using digital simulations to infer the mechanism. Data analysis shows that despite parallel mechanisms, the concerted one seems to predominate for the oxidant-base pair that renders the most isoenergetic coupled state, whereby a PT with is capable of producing an ET with , as a result of the Nernstian shift of with pKa. In contrast, the stepwise PT-ET appears to dominate when GS- grows in stability as becomes more negative. Understanding the interplay between ET and PT will help in the design of catalysts for energy harvesting processes that rely on proton-coupled electron transfer.

A Bioactive Carbon Nanotube-Based Ink for Printing 2D and 3D Flexible Electronics

The development of electrically conductive carbon nanotube-based inks is reported. Using these inks, 2D and 3D structures are printed on various flexible substrates such as paper, hydrogels, and elastomers. The printed patterns have mechanical and electrical properties that make them beneficial for various biological applications.

In Situ Derivatization of an Intrinsic Iron Impurity as a Surface-Confined Iron(II)tris(2,2'-bipyridine) Complex on MWCNT and Its Application to Selective Electrochemical Sensing of DNA's Purine Bases

The derivatization of an intrinsic iron impurity in a carbon nanotube (CNT-*Fe, *Fe-intrinsic, and redox-active iron impurity) as a functional molecular system has been challenging to realize. There are certain limitations on the derivatization of such iron impurities such as low concentration and limited accessibility. Herein, we report an in situ electroassisted derivatization of an intrinsic and redox-active iron impurity in a multiwalled carbon nanotube (MWCNT-*Fe, *Fe, 2.1 wt %) as MWCNT-*Fe(bpy)3(2+), where Fe(bpy)3(2+) = iron(II)tris(2,2'-bipyridine) complex and bpy = 2,2'-bipyridine. The hybrid complex was prepared by the electrochemical treatment of a 2,2'-bipyridine ligand adsorbed {MWCNT-*Fe + Nafion} modified glassy carbon electrode in pH 7 phosphate buffer solution. This new MWCNT-*Fe(bpy)3(2+) hybrid electrode showed well-defined, stable redox at E1/2 = 830 mV with a peak-to-peak separation (ΔEp) of 72 mV in a neutral pH solution. This is quite different from an ex situ Nafion-Fe(bpy)3(2+) complex system that showed an unstable response at neutral pH. This in situ approach can allow the redox-active iron impurity in the CNTs to be quantified using the current signal of the Fe(bpy)3(2+) hybrid system. This MWCNT-*Fe(bpy)3(2+) hybrid modified electrode was further used as an electrochemical detector for selective and separation-less flow injection analysis of DNA's purine bases, adenine and guanine, without interference from pyrimidine bases, cytosine, and thymine at different oxidative detection potentials of 1 V (for adenine and guanine) and 0.7 V vs Ag/AgCl (for guanine) using the pH 7 phosphate buffer solution as a carrier system.

Hybrids of Nucleic Acids and Carbon Nanotubes for Nanobiotechnology

Recent progress in the combination of nucleic acids and carbon nanotubes (CNTs) has been briefly reviewed here. Since discovering the hybridization phenomenon of DNA molecules and CNTs in 2003, a large amount of fundamental and applied research has been carried out. Among thousands of papers published since 2003, approximately 240 papers focused on biological applications were selected and categorized based on the types of nucleic acids used, but not the types of CNTs. This survey revealed that the hybridization phenomenon is strongly affected by various factors, such as DNA sequences, and for this reason, fundamental studies on the hybridization phenomenon are important. Additionally, many research groups have proposed numerous practical applications, such as nanobiosensors. The goal of this review is to provide perspective on biological applications using hybrids of nucleic acids and CNTs.

Potentiometric, electronic, and transient absorptive spectroscopic properties of oxidized single-walled carbon nanotubes helically wrapped by ionic, semiconducting polymers in aqueous and organic media

We report the first direct cyclic voltammetric determination of the valence and conduction band energy levels for noncovalently modified (6,5) chirality enriched SWNTs [(6,5) SWNTs] in which an aryleneethynylene polymer monolayer helically wraps the nanotube surface at periodic and constant morphology. Potentiometric properties as well as the steady-state and transient absorption spectroscopic signatures of oxidized (6,5) SWNTs were probed as a function of the electronic structure of the aryleneethynylene polymer that helically wraps the nanotube surface, the solvent dielectric, and nanotube hole polaron concentration. These data: (i) highlight the utility of these polymer-SWNT superstructures in experiments that establish the potentiometric valence and conduction band energy levels of semiconducting carbon nanotubes; (ii) provide a direct measure of the (6,5) SWNT hole polaron delocalization length (2.75 nm); (iii) determine steady-state and transient electronic absorptive spectroscopic signatures that are uniquely associated with the (6,5) SWNT hole polaron state; and (iv) demonstrate that modulation of semiconducting polymer frontier orbital energy levels can drive spectral shifts of SWNT hole polaron transitions as well as regulate SWNT valence and conduction band energies.