Development of electrochemical sensors for selective detection of biological biomarkers and novel nanostructure to improve measurement sensitivity

Abstract

The major goal of this thesis was to fabricate electrochemical biosenors for the detection of Anthrax and develop versatile nanostructures to improve the performance of electrochemical measurement. In Part I, a short chain peptide (16mer) was successfully utilized for the selective electrochemical detection of the protein biomarker, protective antigen (PA), for the diagnosis of Anthrax. Since the size of the peptide was approximately 1~2 orders of magnitude smaller than that of the antibody, a more populated immobilization of peptide on the sensing layer was possible and eventually led to improved sensitivity for PA detection. The limit of detection (LOD) for was 5.2 pM. Sensitivity of PA detection was further improved by directly immobilizing a PA-specific peptide onto a multi-wall carbon nanotube (MWCNT). The MWCNT was covalently immobilized onto a polyaniline (PANI) electrode. Then, the PA-specific peptide was covalently immobilized to the MWCNT layer for measurement. By this way, an insulating self assembled organic layer in the previous sensing layer could be eliminated, thereby enhancing electron transfer across the sensing layer and resulting in LOD of 0.4 pM. In Part II, a strategy for efficient arrangement of gold microelectrodes to build an optimal array sensor and novel nanostructures able to improve the performance of electrochemical measurement have been demonstrated. First, a simply and reproducible carbon microelectrode array (CMA) was constructed and used as a frame to build gold (Au) microelectrode array sensor. To efficiently utilize space in a sensor and make sensor preparation simple, carbon fibers were oriented as a spiral fashion by rolling these around Cu wire. The distance among carbon fibers was carefully determined to avoid overlap among individual diffusion layers. After preparation of the spirally arranged CMA, Au film was formed on the surface of individual electrodes. Then, the Au-film CMA sensor was used to measure Hg2+ in a low concentration range. Second, a three dimensional (3D) Au nanodendrite network porous structure was constructed on a platinum surface through electrodeposition of Au under the presence of hydrogen bubble generated from the same surface. Iodide, used as a co-reagent, played an important role in the construction of the nanodendrite network by preventing continual growth of Au into larger agglomerates as well as inhibiting coalescence of neighboring nanodendrites. An electrochemical sensor incorporating the structure was built and used to detect As (III) in ultra low concentration range. Finally, a simple N-doping method to efficiently increase the concentration of quaternary N out of total doped nitrogen as well as decrease oxygen in graphene structure has been described. To meet the goal, two separate reactions were combined consecutively; reduction of graphene oxide (GO) first and then annealing of the reduced graphene (RGO) under NH3 environment for N-doping. For the identification of three different types of doped nitrogen and determination of atomic composition of the samples, X-ray photoelectron spectroscopy (XPS) was used. In addition, the sheet resistance of the samples was also measured to examine the variation of electro-conductivity according to the reaction conditions. To examine the electrochemical characteristics of the prepared samples, cyclic voltammograms (CVs) of K3Fe(CN)6 and H2O2 solution were measured.