Carbon nanotube modified electrode in the applicat

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Carbon nanotube modified electrode in the application in biosensors

Abstract In this paper, chemically modified electrode based on carbon nanotubes and Advances in biological sensors. Key words Carbon nanotubes; modified electrode; biological sensors; progress electron microscopy of Japan since 1991, Iijima discovered carbon nano-experts tubes (carbon nanotubes, CNTs) since, CNTs because of their unique mechanical, electronic and chemical properties, a world-wide research focus. It can be considered to be folded into the carbon-graphite cylinder results, divided into MWNTs (MWNTs) and SWNTs (SWNTs). In recent years, with the depth of the properties of CNTs, more and more people will be the field of CNTs used in bio-sensors, as a new type of electrode material, and achieved the desired results. Chinese papers League finishing. 1 Characteristics of Carbon Nanotubes Research CNTs also known as the nanotube, the carbon lines belonging to Fuller, seamless hollow tube, with a complete molecular structure, the six-carbon ring composed of planar coil made of graphite [1]. Pipe at both ends of the single pentagon or heptagon by the participation closed. CNTs by each carbon atom with sp2 hybridization of carbon atoms around the three form a hexagonal grid structure attached to, but usually have curved due to the formation of topological structure, so that some of the carbon atoms sp3 hybridization state [2]. The size of CNTs in the atoms, molecules, represented by the junction of microscopic objects and macroscopic objects, the transition region so that both typical and atypical macro-micro system, system, which has a substantial surface effect, volume effect, quantum effect and macroscopic quantum tunneling [3]. Explore and study the new properties of the carbon electrode structure is of great significance. Both single-walled or multi-wall CNTs can be used to produce CNTs modified electrode, and its electro-catalytic, electrical analysis of chemical and biological sensors, etc. that has broad application prospects. 2 CNTs modified enzyme sensor compared with other methods, electrochemical biosensor is portable, low cost, high sensitivity, good stability, etc., coupled with the CNTs themselves catalytic and sensitizing effects, making the biosensor based on CNTs have broad application prospects. Enzyme sensor is a biosensor research and application of the most one is the most typical representative of the biosensor. CNTs as an enzyme immobilization material, but also as a basis for the modification of the electrode material is a new type of CNTs sensor modifying enzyme sensor [4], such sensors have many advantages. CNTs and electrodes in accordance with the basis of the different ways of modifying enzyme sensor can be divided into CNTs irreversible adsorption type, paste type, in situ growth (array) type, covalently bonded and other types. 2.1 absorption-type CNTs modified enzyme sensor is a very simple and effective adsorption and ancient method of electrode modification, CNTs can be adsorbed by van der Waals force base electrode surface, and sometimes the electrode surface also covered with protective film to prevent loss of CNTs, but also play a protective role of the enzyme. Azamian et al [5] method using adsorption of SWNTs fixed in a glassy carbon electrode, made of GOD  SWNTs modified glassy carbon electrode. Cai et al [6] studied the CNTs modified glassy carbon electrode direct electron transfer of GOD on the experimental results show that the GOD electrode in GCPCNT maintain their bio-electrical activity, showed the direct electron transfer. 2.2 modifying enzymes CNTs paste type sensor paste type electrode is cylindrical electrode, which is a mixture of CNTs and insulators in the system, in which the CNTs is not only a modification of the electrode material is also the subject of such electrodes, plays the role of conductivity. This macro-like build modified Maria et al in 2004 [7] The MWNTs, mineral oil and glucose oxidase CNTs paste electrodes made from glucose, and the results showed that: the electrode glucose selectivity and high sensitivity, lower detection limit and wide linear range; Federica et al [8] made use of SWNTs CNTs paste electrode, the electrode with the traditional carbon paste electrode compared with the cathodic peak potential difference decreases, the anodic peak current increases,[link widoczny dla zalogowanych], the reversible and sensitivity. 2.3 CNTs modified enzyme sensor array type Preparation of CNTs under normal circumstances when, CNTs are free growth will occur at random bending and winding each other, causing a great impact. Therefore, the preparation of highly consistent orientation, diameter uniformity and purity of the CNTs arrays become a hot topic. Gao et al [9], iron phthalocyanine under high temperature pyrolysis, prepared on quartz glass substrates vertical growth of CNTs array. CNTs first sputtering a layer of Au film on the array, and then plated conductive polymer film, GOD as a biosensor platform architecture. Tang et al [10], the growth orientation of CNTs in situ on the electroplated Pt, and then dipping in the GOD solution, and finally coated with Nafion membrane, which obtained the linear range of the sensor, the detection limit, response time, sensitivity and stability and other areas have very excellent performance. 2.4 CNTs covalently modified enzyme-based sensors in Au, Pt, C, and other basic organic functional layer of the electrode membrane surface modification can improve the effect of pretreatment, such a large number of film groups in the role of reagents and reaction of the carboxyl end of CNTs, which will covalently CNTs. Patolsky et al [11] first reported oxidoreductase CNTs modified electrode surface reconstruction of Au electrode surface covered by a layer of 2  mixture of mercaptan and cystamine, experiments show that electron transfer rate determined by the length of SWNTs. Liu et al [12] The study also obtained similar results. Domestic scholars Xue et al [13] will be fixed SWNTs as a biological sensor materials, the carboxylic acid functionalized SWNTs coated on the platinum electrode to form a glucose biosensor, the biosensor in a wide range of pH values show a stable voltammetric response, and after four months 90% of the activity remained high stability. 3 CNTs in the application of DNA biosensors DNAs biosensor can generally DNA probe and DNA hybridization, or other information into a measurable signal of the transducer in two parts composition. DNA probes are usually fixed to the electrode surface, and then identified based on hybridization properties of DNA molecules were detected on the target genes. China's recent DNA electrochemical biosensor and its product testing in transgenic plants has been some work applications [14], but limited by the detection process as a hybridization indicator of the limitations of the electroactive materials, limit of detection experiments and accuracy is not very satisfactory. As we all know, DNA molecule itself is an electric activity (caused by base), earlier studies mostly based on this. Recently, the use of CNT properties, DNA modification in the CNTs or CNTs on the electrochemical behavior of solid electrodes have been widely studied and applied [15  18]. General terms, mainly concentrated in three major directions: First, the DNA probes fixed on a large surface area and strong adsorption of CNTs on the preparation of hybrid sensor [17]; the second is the study of electrical activity on the part of DNA or in the CNTs directly on the CNTs modified electrode electrochemical behavior [15  16]; Third, by analyzing the interaction between CNTs and DNA to obtain DNA sequence information [18]. With the improvement of production process and the preparation / modified electrode pre-treatment technology to further improve, CNTs DNA biosensor is expected to make greater overall performance improvement.