Abstract
We investigate the design, characterization, and application of metallic photonic crystal (MPC) structures, consisting of plasmonic gold nanogratings on top of a photonic waveguide, as transducers for lab-on-chip biosensing in cryogenic environments. The compact design offers a promising approach to sensitive, in situ biosensing platforms for astrobiology applications (e.g., on the "icy moons" of the outer solar system). We fabricated and experimentally characterized three MPC sensor geometries, with variable nanograting width, at temperatures ranging from 300 K to 180 K. Sensors with wider nanogratings were more sensitive to changes in the local dielectric environment. Temperature-dependent experiments revealed an increase in plasmonic resonance intensity of around 13% at 180 K (compared with 300 K), while the coupled plasmonic-photonic resonance was less sensitive to temperature, varying by less than 5%. Simulation results confirm the relative temperature stability of the plasmonic-photonic mode and, combined with its high sensitivity, suggest a novel application of this mode as the sensing transduction mechanism over wide temperature ranges. To our knowledge, this is among the first reports of the design and characterization of a nanoplasmonic sensor specifically for low-temperature sensing operation.
Highlights
Plasmonic sensors, based on surface plasmon resonance (SPR), have found wide application to biosensing and medical diagnostics, because of their high sensitivity, label-free biomolecular identification, compatibility with biological targets, and integration with microfluidic systems [1,2,3]
We have designed, fabricated, and experimentally characterized metallic photonic crystal (MPC)-based sensors for application to lab-on-chip sensing in cryogenic environments
The sensitivity enhancement trends were confirmed qualitatively using full wave electromagnetic simulations in CST Microwave Studio. These results suggest that nanograting width should be considered as a design parameter for the optimization of MPC-based sensors, in addition to grating period and waveguide thickness
Summary
Plasmonic sensors, based on surface plasmon resonance (SPR), have found wide application to biosensing and medical diagnostics, because of their high sensitivity, label-free biomolecular identification, compatibility with biological targets, and integration with microfluidic systems [1,2,3]. Under appropriate conditions (i.e., polarization, frequency, and angle of incidence), incident light is coupled into hybrid plasmonic-photonic modes, which have been demonstrated to have higher sensitivity to the local environment than their constituent plasmonic or photonic elements separately [21] These sensors have been applied to hydrogen sensing [22], HIV antibody detection [21], and molecular binding dynamics [24]. Nanogratings of approximately 200 nm in width and 35 nm in height excite a plasmonic resonance in this range to fulfill this requirement While both of these parameters influence the optical properties of the MPC structures, the grating width plays a much larger role (see Appendix A), especially towards exciting the coupled plasmonic-photonic modes used for our sensing application.
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