Study On High Sensitive Electrochemical Immunosensors And Aptamers Constructed By Nano-materials

With the development of nanotechnology, the use of nanomaterials to fabricate electrochemical biosensors has attracted widespread interest, due to their unique mechanical, electrical and optical properties, such as high surface-to-volume ratio, good stability, small dimension effect, good biocompatibility and strong adsorption ability. Particularly attractive for numerous bioanalytical applications are gold nanoparticles, barcode quantum dot (QD) nanoparticles and carbon nanotubes (CNTs).Electrochemical immunosensors have become a powerful tools designed to detect the protein, due to their advantages such as simple preparation, low cost, fast analytical time, small size and sensitive platform. Aptamers are synthetic oligonucleotides, which possess specific recognition abilities to various targets ranging from small molecules to large proteins. Because of their high selectivity, stability, and easy regeneration capabilities over traditional antibodies, aptamers as recognition elements is widely attracted in bioapplications by researchers.Part 1 Sensitive label-free immunoassay of carcinoembryonic antigen based on Au-TiO2 hybrid nanocomposite filmIn this paper, a new nanostructured Au-TiO2 particle was synthesized and employed for the construction of a label-free amperometric immunosensor for carcinoembryonic antigen (CEA) determination. The spherical Au-TiO2 nanoparticles provided a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, had large surface-to-volume ratio, film-forming ability and high stability. The Au-TiO2 nanoparticles were characterized by transmission electron microscopy (TEM). The fabrication process of the electrochemical immunosensor was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques.Part 2 Reverse-micelle synthesis of electrochemically encoded quantum dot barcodes: application to electronic coding of a cancer marker Reproducible electrochemically encoded quantum dot (QD) barcodes were prepared using the reverse-micelle synthetic approach. The encoding elements, Zn2+, Cd2+, and Pb2+ were confined within a single QD, which eliminates the cumbersome encapsulation process used by other common nanoparticle-based barcode preparation schemes. The new synthetic approach also leads to reproducible preparation of the barcode QDs. The distinct voltammetric stripping patterns of Zn2+ Cd2+, and Pb2+ at distinguishable potentials with controllable current intensities offer excellent encoding capability for the proposed electrochemical (EC) QDs. Additionally, the simultaneous modification of the QD barcode surface with organic ligands during the preparation process make them potentially useful in biomedical research. For proof of concept of their application in bioassays, the EC barcoded QDs were further employed as tags for an immunoassay of a cancer marker, carcinoembryonic antigen (CEA). The synthesized EC barcode hybrid QDs hold considerable potential in biodetection, encrypted information, and product tracking.Part 3 Ultrasensitive aptamer-based protein detection via a dual amplified biocatalytic strategyWe present an ultrasensitive aptasensor for the electronic monitoring of proteins through a dual amplified strategy in this paper. The target protein thrombin is sandwiched between an electrode surface confined aptamer and an aptamer-enzyme-carbon nanotube bioconjugate. The analytical signal amplification is achieved by coupling the signal amplification nature of multiple enzymes with the biocatalytic signal enhancement of redox-recycling. Our novel dramatic signal amplification strategy, with a detection limit of 8.3 fM, shows about 4 orders of magnitude improvement in the sensitivity for thrombin detection compared to other universal single enzyme-based assay. This makes our approach an attractive alternative to other common PCR-based signal amplification in ultralow level of protein detection.