Guided-mode resonance on pedestal and half-buried high-contrast gratings for biosensing applications

Optical sensors typically provide compact, fast and precise means of performing quantitative measures for almost any kind of measurand that is usually probed electronically. High-contrast grating (HCG) resonators are known to manifest an extremely sharp and sensitive optical resonance and can constitute a highly suitable sensing platform. In this paper we present two advanced high-contrast grating designs improving the sensing performances of conventional implementations. These configurations, namely pedestal and half-buried HCGs, allow to enhance the shift of the photonic resonance while maintaining the spectral features of the standard configuration. First, the spectral feature of the HCGs was numerically optimized to express the sharpest possible resonance when the structure is immersed in serum. Second, the sensing properties of conventional and advanced HCG implementations were studied by modelling the biological entities to be sensed as a thin dielectric coating layer of increasing thickness. Pedestal HCGs were found to provide a ∼ 12% improvement in sensitivity and a six-fold improvement in resonance quality factor (Q-factor), while buried HCGs resulted in a ∼ 58% improvement in sensitivity at the expense of a slightly broader resonance. Such structures may serve as an improved sensitive biosensing platform for near-infrared spectroscopy.