No abstract

The band gap of indium gallium nitride can be tuned by varying the compositional ratio of indium to gallium, spanning the entire visible region and extending into the near-infrared and near-ultraviolet. This tunability allows for device optimization specific to different applications, including as a biosensor or platform for studying biological interactions. However, these rely on chemically dependent interactions between the device surface and the biostructures of interest. This study presents a material gradient of changing In:Ga composition and the subsequent evaluation of amino acid adsorption to this surface. Arginine is adsorbed to the surface in conditions both above and below the isoelectric point, providing insight to the role of electrostatic interactions in interface formation. These electrostatics are the driving force of the observed adsorption behaviors, with protonated amino acid demonstrating increased adsorption as a function of native surface oxide buildup. We thus present a gradient inorganic substrate featuring varying affinity for amino acid adhesion, which can be applied in generating gradient architectures for biosensors and studying cellular behaviors without application of specialized patterning processes.

III-nitride materials have recently received increasing levels of attention for their potential to successfully interface with, and sense biochemical interactions in biological systems. Expanding on available sensing schemes (including transistor-based devices,) a III-N lateral polarity structure capable of introducing quasi-phase matching through a periodic polarity grating presents a novel platform for second harmonic generation. This platform constitutes a non-linear optical phenomenon with exquisite sensitivity to the chemical state of a surface or interface. To characterize the response of a biological system to the nanostructured lateral polarity structures, we cultured neurotypic PC12 cells on AlGaN with varying ratios of Al:Ga - 0, 0.4, 0.6, and 1 - and on surfaces of varying pitch to the III-polar vs. N-polar grating - 5, 10, 20 and 50 μm. While some toxicity associated with increasing Al is observed, we documented and quantified trends in cell responses to the local material polarity and nanoscale roughness. The nitrogen-polar material has a significantly higher nanoscale roughness than III-polar regions, and a 80-200 nm step height difference between the III-polar and N-polar materials in the lateral polarity configuration generates adequate changes in topography to influence cell growth, improves cell adhesion and promotes cell migration along the direction of the features. As the designed material configuration is further explored for biochemical sensing, the lateral polarity scheme may provide a route in assessing the non-specific protein adsorption to this varying nano-topography that drives the subsequent cell response.