Sensitivity enhancement in photonic crystal slab biosensors

Mohamed El Beheiry,Shanhui Fan,Victor Liu,Ofer Levi

doi:10.1364/oe.18.022702

Abstract

Refractive index sensitivity of guided resonances in photonic crystal slabs is analyzed. We show that modal properties of guided resonances strongly affect spectral sensitivity and quality factors, resulting in substantial enhancement of refractive index sensitivity. A three-fold spectral sensitivity enhancement is demonstrated for suspended slab designs, in contrast to designs with a slab resting over a substrate. Spectral sensitivity values are additionally shown to be unaffected by quality factor reductions, which are common to fabricated photonic crystal nano-structures. Finally, we determine that proper selection of photonic crystal slab design parameters permits biosensing of a wide range of analytes, including proteins, antigens, and cells. These photonic crystals are compatible with large-area biosensor designs, permitting direct access to externally incident optical beams in a microfluidic device.

Highlights

The ability to detect biologically active molecules is of crucial importance for fundamental studies in biochemistry, applications in drug development, and point-of-care diagnostics
We have presented a theoretical analysis of guided resonances in photonic crystal slab (PCS) structures for biosensing
We have reviewed the underlying physics and the engineering aspects in selecting a symmetric or asymmetric PCS topology

Summary

Introduction

The ability to detect biologically active molecules is of crucial importance for fundamental studies in biochemistry, applications in drug development, and point-of-care diagnostics. Many recent research efforts have focused on the study of two-dimensional planar PC structures, where light is coupled to in-plane guided modes from the narrow facet of a slab, as the review by Mortensen et al describes [26] Coupling light into such PC structures is challenging as a matching waveguide section may be needed to couple between the free space incident beam and the small mode size inside the PC structure. Theoretical studies of guided resonance modes for biosensing have evaluated a PCS embedded with spherical voids to capture analytes as well as using a pair of PCS structures as tunable dielectric mirrors to enhance sensitivity [34,35].

Computational methods

Measures of sensitivity

Guided resonance modes

Asymmetric structures

Biosensing

Conclusion