Surface Functionalization Of Carbon Nanotube Fiber Electrode And Its Application In Ascorbic Acid Detection

Ascorbic acid(AA) plays an important role in human body: it not only participates in various redox reactions to remove free radicals, but also helps to synthesis and transport many important compounds...Recent studies also shows that AA deficiency in brain may be associated with the brain disorder, which might be a sign of neurodegenerative diseases. It is expected to be used for the diagnosis of cerebral diseases such as ischemic stroke, Alzheimer’s disease, Parkinson’s disease and Huntington’s disease. However, due to the lack of accurate and real-time testing method of AA concentration, what’s physiological mechanism of AA in brain is still unclear. Carbon nanotubes attracts considerable attentions due to its excellent conductivity. Large amounts of researches have been conducted on this kind of functional carbon materials modified electrodes used as biosensors. However, it is still a challenge to design and synthesize functionalized carbon nanotubes as the electrochemical probe for the on-line measurement in living tissue, as which requests several specific requirements such as high selectivity and accuracy, long-term stability, and good biological compatibility.The noval carbon nanotube fiber, which was synthesized through chemical vapor deposition by Peng Huisheng group, is made into the microelectrodes after pretreatment.Various methods including Raman spectra, XPS, Scanning electron microscopy and Transmission electron microscopy, were used to find out the effect of electrochemical activation on the fibers. The electrochemistry behaviors of electrodes were also studied. Results showed that the electrochemical activation process not only increased the surface oxygen content and structure defects of fibers, but also improved the electrochemical activity of the carbon nanotube fiber electrodes for AA oxidation. The relationship between the structure defects of the fibers and its electrochemical activity has been further confirmed through a systemic study on the carbon nanotube fiber electrodes with different surface oxygen content and structure defects.The carbon nanotube fiber was also used as an accurate microsensor for electrochemical ratiometric detection of AA in live brain. The rat that has an Alzheimer’s disease is studied as a demonstration. The oxidation of AA is greatly facilitated at the surface of this fibre microsensor with a low potential, leading to a high selectivity against potential interferences in brain. Meanwhile, an unexpected separated peak from the fibre surface stays constant with the increasing AA concentration, thus providing a real-time and ratiometric detection with high accuracy. To the best of our knowledge, this work represents the first report on accurately detecting the AA concentration in live brain with Alzheimer’s disease.