ElectrochemicalDetectionofNitricOxideonaSWCNT/RTILCompositeGelMicroelectrode资源-CSDN下载

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单壁碳管为基的一氧化氮传感器

Electrochemical Detection of Nitric Oxide on a SWCNT/RTIL

Composite Gel Microelectrode

Chang Ming Li

, Jianfeng Zang

a,b

, Dongping Zhan

, Wei Chen

, Chang Q. Sun

Ai. L.

Teo

, Yek. T. Chua

Vee. S. Lee

, Shabbir. M. Moochhala

School of Chemical and Biomedical Engineering, Nanyang Technological University, Nanyang Avenue,

Singapore 639798.

School of Electrical and Electronic Engineering, Nanyang Technological University,

Nanyang Avenue, Singapore 639798.

Defense Medical & Environmental Research Institute, DSO

National Laboratories, Singapore 117510.

* To whom correspondence should be addressed. E-mail: ecmli@ntu.edu.sg

Abstract

Single walled carbon nanotubes (SWCNT) and room temperature ionic liquid (RTIL)

were used to make a gel microelectrode for studies of the oxidation of nitric oxide (NO).

The Faraday response of the gel microelectrode was contributed from two components:

an outside-surface microdisk and a thin-layer cell formed by inner porous electrode

materials, and enhanced by the thin-layer effect. An EC mechanism, electrochemical NO

oxidation followed by a chemical oxidation, was proposed. The gel microelectrode with a

Nafion

coating eliminated interferences from nitrite and some biomolecules, improved

stability, and had a linear response range from 100 nM to 100 µM.

Keywords: Gel microelectrode, NO oxidation, NO sensor, Carbon nanotubes, Room

temperature ionic liquid

1. Introduction

Nitric oxide has been found to be released by many cells in mammalian systems to play a

number of important biological roles such as neurotransmitter, cytostatic agent, blood

pressure regulator [1], and has also been implicated in the pathogenesis of several

diseases, due to deficiency or excess concentration of NO [2]. From a biochemical as

well as a medical perspective, it is important to quantify NO generated in abnormal and

normal tissues, including in-vivo measurements. However, NO reacts rapidly with

hemoglobin, oxygen and other biological species in vivo or in vitro. At the presence of

superoxide, NO is rapidly converted to peroxynitrite. Consequently, NO has a half-life

period of two to six seconds in vivo. Thus, the detection of NO in biological systems is

difficult.

NO detection has been reported with spectroscopic, chromatography and

electrochemical methods [3-5]. Mass spectroscopy and gas chromatography for NO

detection are not sensitive. Reported spectroscopic methods also include UV-visible

spectroscopy, electron spin resonance spectroscopy, and fluorescence emission

spectroscopy or spin trapping. Electrochemical detections offer several prominent

features that are not available for the spectroscopic analysis, which include the capability

of employing microelectrodes in situ measurement of NO in single cells near the source

http://www.paper.edu.cn

of NO synthesis (nitric oxide synthase, NOS), the direct NO detection based on electron

exchange between NO and an electrode, and a portable detection instrument [2, 6, 7].

Electrochemical detection of NO is based on its oxidation because its reduction

reaction often interfered by oxygen. The main challenges to improve the performance of

NO sensors are: (i) adopting the selective polymer membrane to exclude the interference

from some biological species such as nitrite anions, ascorbic acid, dopamine and L-

arginine; (ii) significantly improving the sensitivity for low detection limit. Polymeric

porphyrins as electrocatalysts have been reported to improve the sensitivity [6-8].

Recently, nanoparticles and nanotubes as new electrode materials have been use in

electrochemical NO biosensor [9, 10]. However, there is still a need to further develop

new types of NO sensors for performance improvement.

Some superior properties of RTIL such as high thermal stability, wide liquid

range, high conductivity and negligible vapour pressure make it especially promising

toward the sensor application. Ionic liquid based carbon nanotube composite

demonstrated direct electrochemistry of redox proteins [11, 12]. The previously reported

electrodes made from conventional coating method, had poor stability due to the

desquamation of the gel in solution. An upside-down technology based electrode was

adopted to overcome the shortcoming, but it showed a rather large IR drop, which

hampers to obtained the correct kinetic information [13]. In this paper a novel gel

microelectrode based on the hydrophobic IL was employed to prevent the leaching

problems and improve the stability of the NO sensor. Micro-hole electrode, the tip of

which is etched with a cavity, is a powerful tool not only for the investigation of

electrochemical processes but also the application for electrochemical sensors and

devices. Various powder materials could be filled in the cavity to fabricate the powder

microelectrodes, which demonstrated excellent performance in electrocatalysis and

sensor applications [14-18]. In this report, we filled the micro-hole with a conductive gel

composite by SWCNT and ionic liquid to fabricate the gel microelectrode. The

electrochemical properties of the gel microelectrode and its NO sensor application were

investigated.

2. Experimental

2.1. Chemicals and Apparatus

Specimen of

1-Hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF

) was

purchased from Fluka. Single-walled carbon nanotubes (SWCNTs), Nafion

(5% in

ethanol), sulfuric acid (H

), nitrate acid (HNO

), hydrochloric acid (HCl), sodium

nitrite (NaNO

), sodium nitrate (NaNO

), sodium chloride (NaCl), potassium hydroxide

(KOH), phosphate buffered saline (pH=7.4), pyrogallol, potassium ferricyanide

[Fe(CN)

]) were provided by Aldrich. All chemicals were analytical grade or better.

Water used in all experiments was purified with a Millipore Milli-Q system.

Autolab PGSTAT30 (Metrohm Ltd., Switzerland) electrochemical workstation was

employed to perform the electrochemical measurements in a three-electrode cell. A

saturated Ag/AgCl and a platinum wire were employed as the reference and counter

http://www.paper.edu.cn

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