DNA based biosensors for environmental and medical applications

In the present thesis two electrochemical DNA based biosensors were developed using screen printed electrode as transducers. Biosensors are defined as a self-containing integrated devices, capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element which is in contact with a transduction element. The first DNA biosensor realized was applied to the rapid screening of toxic substances. The biosensor was constructed immobilizing a double helix DNA (Calf Thymus DNA) onto screen-printed electrodes. Subsequently, the biosensor was used for the determination of the toxicity of different kinds of common surfactants. Surfactant interactions with double stranded DNA were evaluated measuring the height of the guanine oxidation peak. Indeed, the interactions with toxic substances raises structural and conformational modifications of DNA causing decrease of guanine peak. The intensity of the guanine oxidation peak, was measured through Square Wave Voltammetry (SWV). Moreover, the toxicity of some selected surfactants was investigated both in sea water and tap water, and data were compared to those obtained in acetate buffer. The interaction between surfactants and Calf Thymus DNA in solution and adsorbed on the sensor surface was also investigated through FTIR and FTIR-ATR spectroscopy respectively. The second kind of biosensor studied was a Genosensor, that is an analytical device where the biological recognition element is a single strand oligonucleotide sequence. These sequences referred as capture probe are capable to recognize selectively a complementary sequence (RNA or DNA), named target, by a hybridization reaction. Among the sequence probes, modified locked nucleic acid (LNA) and the peptide nucleic acid (PNA) were used. In this case the screen printed electrode Abstract iv was used only as transducer while the hybridization assay was conducted onto paramagnetic micro beads. The genosensor was used for the analytical detection of DNA and RNA sequences. In particular, the analytical properties of PNA and LNA capture probes with classical DNA sequences were compared. Hybridization with RNA target as well as with the corresponding DNA sequence was also performed. Differential pulse voltammetry (DPV) was used to perform the electrochemical measurements