Biofunctionalization and surface studies of semiconductor materials for sensing device fabrication
Creators: name: Cao, Yan
Publisher: name: No Publisher Supplied
Year: 2014

description: This thesis describes the development and study of innovative approaches for stepwise functionalization of semiconductor surfaces.  The methods developed in this thesis were applied to improve the selectivity and sensitivity of sensor devices.  The research projects involved in this thesis encompass material synthesis, biochemical functionalization, interfacial analysis, and nano-device development.    Inorganic semiconductor-based sensor devices, including ZnO and MgZnO nanostructured surfaces, and organic semiconductor (rubrene single crystals) were involved in these studies.     1) For inorganic nanomaterial-based sensor devices, we studied the effect of the surface morphology on the capabilities of the nano-sensors.  The surfaces studied were inorganic ZnO nano-structured semiconductors of three morphologies:  nanorod, rough, and planar.  These morphology effect studies were carried out by functionalization of ZnO surfaces with a linker possessing a terminal alkylthiol for coupling to single-stranded DNA.  The resulting ssDNA-functionalized films were then hybridized with complementary ssDNA tagged with fluorescein.  In a selectivity control experiment, no hybridization occurred upon treatment with non-complementary DNA. The ZnO films’ surface functionalization, characterized by FT-IR-ATR and fluorescence spectroscopy and detected on the nano-QCM, was successful on nanorod and rough surfaces but was barely detectable on the planar surface.    The copper-free click reaction was successfully explored as a surface functionalization methodology for ZnO and MgZnO nanorod films.  11-Azidodecanoic acid was bound to ZnO and MgZnO nanorod films through the carboxylic acid moiety, leaving an azide group available for Cu-free click reaction with alkynes.  The azide-functionalized layer was used to immobilize various molecules, either a fluorescent probe, for example pyrene, or a small bioactive molecule, for example biotin or folic acid, capped with an alkyne.  The immobilization of pyrene on the surface was probed by fluorescence spectroscopy, and immobilization of biotin was confirmed by binding with streptavidin-fluorescein isothiocyanate.  The functionalization of ZnO and MgZnO films was monitored by FT-IR-ATR, steady-state fluorescence emission, fluorescence microscopy, and FESEM.    Additionally, in a side development of the step-wise functionalization of inorganic semiconductor surfaces, this thesis proposed a pyrene-cucurbit[8]uril host-guest system to control binding orientation on nanostructured ZrO2 and TiO2 semiconductor surfaces.  The fluorescence emission spectra were mainly used to study the binding orientation on surfaces.  With encapsulation of pyrene-based chromphore into CB8 to form a guest@host complex, the sharp blue-shifted monomer peak was presented in emission spectra and it helped to suppress the formation of excimer.   2) For organic semiconductor material, rubrene single crystal surface was functionalized with a trichlorosilane or diazonium salt as an anchor group, leaving an azide functional group for further Click Chemistry to immobilize various molecules.  The modification to the rubrene surface was monitored by conductivity changes and Hall measurements.