Abstract
The effects of structural design parameters on the performance of nano-replicated photonic crystal (PC) label-free biosensors were examined by the analysis of simulated reflection spectra of PC structures. The grating pitch, duty, scaled grating height and scaled TiO2 layer thickness were selected as the design factors to optimize the PC structure. The peak wavelength value (PWV), full width at half maximum of the peak, figure of merit for the bulk and surface sensitivities, and surface/bulk sensitivity ratio were also selected as the responses to optimize the PC label-free biosensor performance. A parametric study showed that the grating pitch was the dominant factor for PWV, and that it had low interaction effects with other scaled design factors. Therefore, we can isolate the effect of grating pitch using scaled design factors. For the design of PC-label free biosensor, one should consider that: (1) the PWV can be measured by the reflection peak measurement instruments, (2) the grating pitch and duty can be manufactured using conventional lithography systems, and (3) the optimum design is less sensitive to the grating height and TiO2 layer thickness variations in the fabrication process. In this paper, we suggested a design guide for highly sensitive PC biosensor in which one select the grating pitch and duty based on the limitations of the lithography and measurement system, and conduct a multi objective optimization of the grating height and TiO2 layer thickness for maximizing performance and minimizing the influence of parameter variation. Through multi-objective optimization of a PC structure with a fixed grating height of 550 nm and a duty of 50%, we obtained a surface FOM of 66.18 RIU−1 and an S/B ratio of 34.8%, with a grating height of 117 nm and TiO2 height of 210 nm.
Highlights
A photonic crystal (PC) is a periodic arrangement of dielectric materials
We performed a parametric study of the effects of structural design factors on the performance of PC label-free biosensors
The bulk and surface figure of merit’ (FOM), S/B ratio, and full width at half maximum (FWHM) were proposed to define the performance of PC biosensors
Summary
A photonic crystal (PC) is a periodic arrangement of dielectric materials. PCs can support guided-mode resonance when the evanescent (cut-off) diffracted orders of a periodic sub-wavelength surface structure couple with the modes of an effective high-index layer. The energy is coupled with ‘leaky modes’ that escape from the structure in both the forward and backward directions because of its diffractive nature They interfere with the directly transmitted and reflected zeroth orders: this leads to a strong reflection about a resonant wavelength whose line width and spectral location are set by the physical parameters of the device [1]. Various approaches for improving the sensitivity of PC label-free biosensors by changing the structural parameters or material properties have been proposed, a full parametric study of the structural design factors on the performance of PC label-free biosensor has not been conducted, which is important to understand the nature of PC label-free biosensor. We applied an optimization method that considers the interaction effects and limits of fabrication/readout instruments as a design guideline for PC label-free biosensors
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