Poly(styrene- alt-maleic acid) adsorption on hydroxyapatite and TiO (rutile) was studied using experimental techniques and complemented by ab initio simulations of adsorption of a maleic acid segment as a subunit of the copolymer. Ab initio calculations suggest that the maleic acid segment forms a strong covalent bonding to the TiO and hydroxyapatite surfaces. If compared to vacuum, the presence of a solvent significantly reduces the adsorption strength as the polarity of the solvent increases. The results of first-principles calculations are confirmed by the experimental measurements. We found that the adsorbed poly(styrene- alt-maleic acid) allowed efficient dispersion of rutile and formation of films by the electrophoretic deposition. Moreover, rutile can be codispersed and codeposited with hydroxyapatite to form composite films. The coatings showed an enhanced corrosion protection of metallic implants in simulated body fluid solutions, which opens new avenues for the synthesis, dispersion, and colloidal processing of advanced composite materials for biomedical applications.
We report on silicon waveguide distributed Bragg reflector (DBR) cavities hybridized with a tellurium dioxide (TeO2) cladding and coated in plasma functionalized poly (methyl methacrylate) (PMMA) for label free biological sensors. We describe the device structure and fabrication steps, including reactive sputtering of TeO2 and spin coating and plasma functionalization of PMMA on foundry processed Si chips, as well as the characterization of two DBR designs via thermal, water, and bovine serum albumin (BSA) protein sensing. Plasma treatment on the PMMA films was shown to decrease the water droplet contact angle from ∼70 to ∼35°, increasing hydrophilicity for liquid sensing, while adding functional groups on the surface of the sensors intended to assist with immobilization of BSA molecules. Thermal, water and protein sensing were demonstrated on two DBR designs, including waveguide-connected sidewall (SW) and waveguide-adjacent multi-piece (MP) gratings. Limits of detection of 60 and 300 × 10−4 RIU were measured via water sensing, and thermal sensitivities of 0.11 and 0.13 nm/°C were measured from 25–50 °C for SW and MP DBR cavities, respectively. Plasma treatment was shown to enable protein immobilization and sensing of BSA molecules at a concentration of 2 µg/mL diluted in phosphate buffered saline, demonstrating a ∼1.6 nm resonance shift and subsequent full recovery to baseline after stripping the proteins with sodium dodecyl sulfate for a MP DBR device. These results are a promising step towards active and laser-based sensors using rare-earth-doped TeO2 in silicon photonic circuits, which can be subsequently coated in PMMA and functionalized via plasma treatment for label free biological sensing.
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