Sensing operations based on hexagonal GaN microdisks acting as whispering-gallery mode optical microcavities

Ink-jet printed, blended polymer-based microdisk resonators for controlling non-specific adsorption of biomolecules

A blended FC-V-50 and TZ-001 polymer-based microdisk laser was fabricated by the ink-jet printing method and used for biosensing applications. The FC-V-50 polymer has a negative charge due to the presence of carboxyl functional groups, and the TZ-001 polymer has a positive charge due to the tertiary amine group at a pH of seven. In biosensing applications, non-specific adsorption due to opposite charges of biomolecules and microdisk surfaces can adversely affect the performance of the biosensor. By mixing FC-V-50 and TZ-001 polymers in different ratios, the microdisk surface charge was controlled, and the non-specific adsorption of bovine serum albumin and lysozyme was studied. In addition, the label-free biosensing of streptavidin was demonstrated using a blended polymer-based microdisk laser. This work reports, to the best of our knowledge, the first demonstration of a blended polymer microdisk laser for controlling the non-specific adsorption of biomolecules.

Evanescent Properties of Optical Diffraction from 2-Dimensional Hexagonal Photonic Crystals and Their Sensor Applications

The sensitivity of traditional diffraction grating sensors is limited by the spatial resolution of the measurement setup. Thus, a large space is required to improve sensor performance. Here, we demonstrate a compact hexagonal photonic crystal (PhC) optical sensor with high sensitivity. PhCs are able to diffract optical beams to various angles in azimuthal space. The critical wavelength that satisfies the phase matching or becomes evanescent was used to benchmark the refractive index of a target analyte applied on a PhC sensor. Using a glucose solution as an example, our sensor demonstrated very high sensitivity and a low limit of detection. This shows that the diffraction mechanism of hexagonal photonic crystals can be used for sensors when compact size is a concern.

Microsensors based on a whispering gallery mode in AlGaN microdisks undercut by hydrogen-environment thermal etching

AlGaN microdisks were fabricated via a top-down process using electron-beam lithography, inductively coupled plasma reactive-ion etching, and hydrogen-environment thermal etching from commercial epitaxial wafers with a 100-300 nm thick AlGaN layer grown on a c-plane GaN layer by metal-organic chemical vapor deposition. The hydrogen-environment thermal etching performed well in undercutting the AlGaN microdisks owing to the selective etching for the GaN layer. The AlGaN microdisks acted as the whispering gallery mode (WGM) optical microresonators, exhibiting sharp resonant peaks in room temperature photoluminescence spectra. The evanescent component of the whispering gallery mode (WGM) is influenced by the ambient condition of the microdisk, resulting in the shift of the resonant peaks. The phenomenon is considered to be used for microsensors. Using the WGM in the AlGaN microdisks, we demonstrated microsensors and a microsensor system, which can potentially be used to evaluate biological and chemical actions in a microscale area in real time.