|Ph.D Student||Bussi Yonit|
|Subject||Responsive Nanostructured Porous Si/Polymer Hybrids:|
Synthesis and Characterization
|Department||Department of Nanoscience and Nanotechnology||Supervisor||Professor Ester H. Segal|
Hybrid systems consisting of inorganic porous Si (PSi) hosts combined with polymers are attractive nanomaterials, as they can display a combination of advantageous chemical and physical characteristics not exhibited by the individual constituents. Recent research highlights their potential applications in biosensing, lab-on-chip devices and drug delivery. Importantly, these hybrids can be designed in numerous configurations, which can be tailored to exhibit specific mechanical, chemical, and optical properties for a desired function.
This research focuses on the integration of stimuli-responsive hydrogels into PSi hosts of different nano-morphologies via various bottom-up synthetic techniques, allowing fabrication of sophisticated optical architectures with programmable properties. The unique optical characteristics of the PSi structures are employed for "real-time" monitoring of the responsiveness of the hybrids to external stimuli via reflective interferometric Fourier transform spectroscopy (RIFTS) and photoluminescence (PL) measurements.
We first describe the syntheis and characterization of different responsive PSi/hydrogel hybrid systems with a double-layered morphology, in which the responsive hydrogel layer caps the pores of the oxidized PSi (PSiO2) film. A "capping" hydrogel layer is achieved by partial infiltration of the hydrogel into the porous nanostructure. The optical properties of the porous scaffold provide a means for monitoring "real-time" changes in the PSiO2/hydrogel hybrid, occurring during its fabrication and functionalization. RIFTS is used to characterize the structure of the hybrids as well as their optical response to a variety of external triggers, e.g., enzymes, pH and light. We also demonstrate the feasibility of loading and releasing a model drug, Cannabidiol - an effective anticancer drug, from these PSi-based hybrids.
Next, we describe the design of two optically-responsive PSiO2/hydrogel hybrid architectures, in which a pH-responsive hydrogel, a poly(2-dimethylaminoethyl methacrylate) [poly(DMAEMA)], is used. The first example demonstrates that integration of this hydrogel with chemically-oxidized PSi significantly enhance its PL intensity and long-term stability under physiologically relevant conditions. Moreover, these hybrids change their PL intensity upon pH cycling in a reversible and reproducible manner, not exhibited by the neat PSiO2. In another hybrid system, a two-dimensional (2D) periodic macro-PSi array (MPSi) is used as a host for in situ synthesis of coaxial Ge-TiO2 core-shell nanowires (NWs). The latter are confined within the micro-scale pores of the MPSi support, which in turn prevents their collapse upon their wetting. Subsequently, the NWs are used as a template for incorporation of the pH-responsive poly(DMAEMA) hydrogel by surface-initiated atomic transfer radical polymerization (ATRP). The optical properties of the MPSi are employed for studying of the polymer nanotubes synthesis process, as well as monitoring their pH-response using the RIFTS method. This study demonstrated a novel and a generic approach for facile fabrication for responsive hydrogel/polymer nanotubes in a highly controlled manner.