Chemical and biochemical modifications of silicon surfaces

Chemical and biologically modified surfaces play a crucial role in the development of sensor technologies. Interfaces desirable for such applications require long term stability, fast and sensitive transduction of signals, compatibility with microelectronics for highly parallel processes, and the adaptability to continuous, real time sensing. While many efforts have been made to achieve an ideal combination of robust interfacial chemistry and electrical measurements, the use of modified Si surfaces is of particular interest. Therefore, this thesis work has focused on the chemical modification of Si surfaces for biological binding as well as developing electrochemical detection method for DNA hybridization on modified Si surfaces.; Hydrogen terminated Si(001) and (111) surfaces were used to covalently tether organic monolayers via UV-mediated photochemical reactions to provide suitable functionalities for subsequent DNA attachment. X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements were used to optimize these surface reaction conditions. The resulted DNA-modified surfaces demonstrated excellent chemical stability under hybridization conditions.; Iodine terminated Si surfaces were studied and shown reactive toward alkene molecules when exposed to 514-nm light. Studies using polarized light at varied angle of incidence show that the reaction mechanism is mediated by absorption of light in the bulk Si. In addition, it is demonstrated that heavily doped n-type silicon have much greater photo-attachment efficiency than p-type silicon. New insights regarding the mechanism of this type of photoreaction leads to new method for photopatterning a Si surface with specific reactive groups via visible light.; Electrochemical impedance spectroscopy (EIS) was used to investigate changes in interfacial electrical properties that arise when DNA-modified Si (111) surfaces are exposed to solution-phase DNA oligonucleotides with complementary and non-complementary sequences. Exposure to solutions containing complementary DNA molecules produced significant changes in both real and imaginary components of the electrical impedance, while exposure to non-complementary sequences generated negligible responses. Impedance responses of DNA-modified glassy carbon electrodes and silicon electrodes with different doping were compared and equivalent circuit models were proposed for both systems. Correlations between impedance changes upon DNA hybridization and the electrochemical properties of the interfaces are discussed.