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Based on the immobilization of horseradish peroxidase (HRP) in chitosan(CS) on a glassy carbon electrode (GCE) modified with the Au-Pt alloy nanoparticles (NPs) / polyaniline nanotube (nanoPAN) nanocomposite film, a novel hydrogen peroxide biosensor was constructed. The modified processes of GCE were monitored by cyclic voltammetry and electrochemical impedance spectroscopy. Au-PtNPs/nanoPAN/CS had a better synergistic electrochemical effect than did AuNPs/nanoPAN/CS or PtNPs/nanoPAN/CS. The amperometric response of the biosensor towards H 2 O 2 was investigated by successively adding aliquots of H 2 O 2 to a continuous stirring phosphate buffer solution under the optimized conditions. Because Au-PtNPs have unique catalytic properties and good biocompatibility, and especially Au-PtNPs and nanoPAN have synergistic augmentation for facilitating electron-transfer, the biosensor displayed a fast response time (< 2 s) and broad linear response to H 2 O 2 in the range from 1.0 to 2200 mmol L À1 with a relatively low detection limit of 0.5 mmol L À1 at 3 times the background noise. Moreover, the biosensor can be applied in practical analysis and exhibited high sensitivity, good reproducibility, and long-term stability.

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 (BMIMPF 6 , 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 (DE 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 À1. In essence the SWNT&RTIL PE showed high sensitivity, reliability, stability and reproducibility for the detection of DNA.

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