Abstract
Plasmonic chemical and biological sensors offer significant advantages such as really compact sizes and extremely high sensitivity. Biosensors based on plasmonic waveguides and resonators are some of the most attractive candidates for mobile and wearable devices. However, high losses in the metal and complicated schemes for practical implementation make it challenging to find the optimal configuration of a compact plasmon biosensor. Here, we propose a novel plasmonic refractive index sensor based on a metal strip waveguide placed under a waveguide-based racetrack ring resonator made of the same metal. This scheme guarantees effective coupling between the waveguide and resonator and low loss light transmittance through the long-range waveguide. The proposed device can be easily fabricated (e.g., using optical lithography) and integrated with materials like graphene oxide for providing adsorption of the biomolecules on the sensitive part of the optical elements. To analyze the properties of the designed sensing system, we performed numerical simulations along with some analytical estimations. There is one other interesting general feature of this sensing scheme that is worth pointing out before looking at its details. The sensitivity of the considered device can be significantly increased by surrounding the resonator with media of slightly different refractive indices, which allows sensitivity to reach a value of more than 1 μm per refractive index unit.
Highlights
In recent years, researchers proposed various schemes of optical label-free biosensors, which simultaneously have high sensitivity and a small footprint, allowing their integration into electronic devices [1,2]
Despite the fact that plasmonic resonators have a much lower Q-factor compared to photonic ones with few exceptions available [28,29], a sensitivity of about 1.2 μm/refractive index unit (RIU) can be achieved for a biosensor based on a plasmonic micro-ring resonator, whereas the typical sensitivity of biosensors based on photonic resonators does not exceed 0.5 μm/RIU
This paper presented a novel scheme of optical biosensors based on a vertically coupled plasmonic waveguide and racetrack ring resonator
Summary
Researchers proposed various schemes of optical label-free biosensors, which simultaneously have high sensitivity and a small footprint, allowing their integration into electronic devices [1,2]. The development of plasmonics significantly influenced modern biosensing technology and, currently, most commercial optical biosensors are based on surface plasmon resonance (SPR) excited using the Kretschmann configuration [13,14,15,16,17,18]. The other interesting approach in plasmonic biosensing technology is based on the same principles as those used in integrated nanophotonic biosensors. SPR biosensors that are commonly used today; it is much more compact and easier to integrate into digital devices. The simplicity of these schemes is that they do not contain any moving parts, such as rotating prisms in SPR systems, except for a tunable small range laser. Despite the fact that plasmonic resonators have a much lower Q-factor compared to photonic ones with few exceptions available [28,29], a sensitivity of about 1.2 μm/refractive index unit (RIU) can be achieved for a biosensor based on a plasmonic micro-ring resonator, whereas the typical sensitivity of biosensors based on photonic resonators does not exceed 0.5 μm/RIU
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