Biosensors Based On Nanocarbon Materials

Nanoparticles are widely used in different scientific and industric fields because of their unique properties, such as highly catalytic activity, good conductivity and excellent biocompatibility. Owing to the synergic effect of different nanoparticles, composites possess many more excellent properties than those of original ones and have been regarded as the most promising materials in 21st century. In this paper, based on the in-depth study of a series of carbon nanomaterial, we have synthesized high quality nanomaterials and use it to prepare new chemo-biological sensors. The developed sensors for dopamine (DA), glucose and hydrogen peroxide show high sensitivity, low detection limit and rapid response. The major contents of the paper are described as follows:1. EDTA-MWCNTs being prepared and applied to construct Dopamine sensorCarbon nanotubes possess high electrocatalytic active, specific electronic properties which can facilitate electron transfer between the electroactive species and electrode, and have been widely used in the development of biosensors. In order to further modification, multi-walled carbon nanotubes (MWCNTs) were first oxidized by refluxing in concentrated acid (98% H2SO4:HNO3=3:1) to produce carboxylated groups on the wall as well as the ends of the MWCNTs. On the basis of acylation between -COOH groups and -NH2 groups, EDTA-MWCNTs has been successfully prepared and was characterized by infrared (IR). The DA sensor was fabricated by the covalent attachment of gold nanoparticles (AuNPs) and EDTA-MWCNTs on glass carbon electrode (GCE) surface. The Electrochemical tests show that the Au-NPs and EDTA-MWCNTs modified film exhibits excellent sensitivity and selectivity for the dopamine analysis due to the synergic effect of AuNPs and EDTA - MWCNTs. The linear concentration range for dopamine is from 1.0×10-8 to 6.0×10-6 mol·L-1, and the detection limit is 3.0×10-9 mol·L-1. The response of the sensor is very quick and response time is less than 1 s. The method can be applied to detect the dopamine in human urine samples.2. Glucose sensor based on fullerene - enzyme biocompositesC60 is becoming the most focused research area and shows very promising applications in the fabrication of biosensors due to its unique structure and properties. PAMAM-C60-GOx biocomposite was prepared with PAMAM, C60 and Glucose oxidase (GOx) as matrix and used for the construction of biosensors (Chapter 3). The hybrids exhibited excellent electro-biocatalytic activity and the properties of the sensor have been improved remarkably. Using PAMAM-C60-GOx biocomposite to constrcture of biosensers has the following advantages: first of all, higly capacity of PAMAM can increase the loading amount of enzyme and C60 in the surface of the the sensors, which can enhance catalytic activity over a given area. Activity of enzyme in the nanocoposite can be well maintained in the favorable micro-environment which suuplie by PAMAM with similar with that of natural protein structure; secondly, the rapid and direct electron transferring between GOx and Au electrode surface; thirdly, the synergic effect among C60, AuNPs, PAMAM and active site of GOx. Under the optimal conditions, the biosensor showed very high sensitivity to glucose with a current response of 188.5μA·L·mmol-1·cm-2 and fast response within 1 s. The linear range was from 1.5μ·mol L-1 to 2.5 m·mol·L-1 with correction coefficient of 0.9992. The detection limit was confirmed to be 0.8μmol·L-1. The biosensors showed good repeatability and long-time stability. Therefore, this part of the study is very helpful to the development of multi-nanocomposites and the construction of enzyme sensors.3. The graphite oxide (GO) was synthesized for the preparation of simple H2O2 sensorGraphite, one of the most common carbon forms, plays an important part in many fields. GO was synthesized by oxidizing graphite in strong acid and lots of oxygen-containing groups, such as carbonyl, hydroxyl and carboxyl processed in the carbon layers, makes GO strongly polarity,hydrophilic activity as well as certain of chemical activity. In this part of the work, the structure and morphology of graphite oxide prepared from natural graphite according to modified Hummers method were characterized by XRD, SEM, and FT-IR. Then, a simple H2O2 sensor, fabricated by immobilizing GO on Au electrode modified with L-cystine, was investigated by cyclic voltammetric and amperometric experiments in PBS solution using conventional three - electrode system under optimal conditions. The results exhibited excellent electro - catalytic activity and show a fast response within 1s, indicating that graphite oxide is an excellent material and has a promising application prospect in biosensor construction.