Paste electrode based on short single-walled carbon nanotubes and room temperature ionic liquid: Preparation, characterization and application in DNA detection

A paste electrode (SWNT&RTIL PE) has been prepared using carboxylic group-functionalized short single-walled carbon nanotubes (SWNTs) mixed with 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6, one kind of room temperature ionic liquid, RTIL). Its electrochemical behavior was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in comparison with the paste electrode using mineral oil as a binder. Results highlighted the advantages of the paste electrode: not only higher conductivity, but also lower potential separation (Delta E-P), higher peak current (i(p)) and better reversibility towards dopamine (DA), methylene blue (MB) and K-3[Fe(CN)(6)]. The SWNT&RTIL PE could be used to detect the number of guanine bases and adenine bases contents in per mol oligonucleotides according to the current response in the range of 0.05 - 2.0 nM. Based on the current response of guanine bases, oligonucleotides could be detected sensitively in the B-R buffer solution with a detection limit of 9.9 pM. The heterogeneous electron transfer rate constant (k(s)) of guanine bases contents in the oligonucleotides was investigated and its value was 0.90 s(-1). In essence the SWNT&RTIL PE showed high sensitivity, reliability, stability and reproducibility for the detection of DNA.