Development Of Electrochemical DNA Biosensors Based On Nano-Materials

With the increase of knowledge about the mutations of genes being responsible for numerous inherited human disorders, sequence-specific DNA detection has become a topic of substantial interest in the areas of early diagnosis, medicine, epidemic prevention, environmental protection and bioengineering. In this context, many new biological technologies emerged and found their applications in this field. Of them, electrochemical genosensors may offer a promising alternative for faster, cheaper and simpler nucleic acid assays. Consequently there is a considerable enthusiasm towards the development of electrochemical biosensors for DNA hybridization detection. Such biosensors commonly rely on the immobilization of a single stranded DNA sequence that recognizes its complementary DNA sequence by hybridization and the conversion of DNA base-pair recognization event into a useful electrical signal. Electrochemical biosensors are not only uniquely qualified for meeting the size, cost and power requirements of decentralized genetic testing but offers an elegant route for interfacing at the molecular level the DNA recognition and signal-transduction elements. Therefore, they are expected to have a broad prospect of application in clinic examination of inherited diseases and drug screening.Nano-materials, with their size in the range of 1-100 nm, are currently under intense investigation owing to their special properties. Thanks to their small size, these materials exhibit quanta-size effect, small-size effect, surface effect and tunneling effect that differ from both their bulk material and the individual atoms from which they comprised. With these unique properties, they are widely used in the fields of catalysis, optical absorption, medicine, magnetic medium, new materials synthesis and particularly attractive in biological applications.The combination of the unique properties of nanometer-sized materials with the event of Watson-Crick base-pairing interaction makes them excellent candidates for DNA sensors with high sensitivity and selectivity. This dissertation focuses on fabricating electrochemical DNA biosensors by the use of some kinds of nano-materials, developing a sensitive, sequence-specific and quantifiable gene detection method, and establishing the bases for application of electrochemical DNA biosensor to clinic diagnose.The dissertation includes seven chapters:Chapter 1 Introduce the composition and classification of DNA biosensorsThe abstract mainly focuses on the major steps involved in electrochemical biosensfng of DNA hybridization, the formation of the nucleic acid recognization layer, the actual hybridization event, and the conversion of this hybridization event into an electrical signal in detail.Chapter 2 Cadmium sulflde nanocluster-based electrochemical stripping detection ofDNA hybridizationA novel, sensitive electrochemical DNA hybridization detection assay, using cadmium sulfide (CdS) nanoclusters as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the CdS nanocluster--oligonucleotide DNA probe, followed by the dissolution of the CdS nanoclusters anchored on the hybrids and the indirectly determination of the dissolved cadmium ions by sensitive anodic stripping voltammetry (ASV) at a mercury-coated glassy carbon electrode (GCE). The combination of the large number of cadmium ions released from each DNA hybrid with the remarkable sensitivity of the electrochemical stripping analysis for cadmium at mercury-film GCE allows detection at levels as low as 0.2 pmol L-1 of the complementary sequence of DNA.Chapter 3 Lead sulflde nanoparticle as oligonucleotides labels for electrochemicalstripping detection of DNA hybridizationWe report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. The nanoparticle was used as a marker to label a sequence-known oligonucleotide, which was then employed as a DNA probe for identifying...