Optical Biosensors Based on Silicon-On-Insulator Ring Resonators: A Review

Abstract

Recent developments in optical biosensors based on integrated photonic devices are reviewed with a special emphasis on silicon-on-insulator ring resonators. The review is mainly devoted to the following aspects: (1) Principles of sensing mechanism, (2) sensor design, (3) biofunctionalization procedures for specific molecule detection and (4) system integration and measurement set-ups. The inherent challenges of implementing photonics-based biosensors to meet specific requirements of applications in medicine, food analysis, and environmental monitoring are discussed.

Keywords: aptamers; biomaterials; biophotonics; biosensors; integrated optical sensors; lab-on-a-chip; optical sensor; ring resonators; silicon photonics.

Figure 1

(a) Schematic representation of a silicon-on-insulator ring resonator. According to the resonance condition, only selected wavelengths can propagate in the ring and distinct resonance peaks appear in the output spectrum. Typical ring diameter d range from 20 $\mathsf{\mu }$m to 100 $\mathsf{\mu }$m. (b) Molecular binding takes place if a sample of the analyte gets in touch with the adsorbed layer on top of the silicon waveguide leading to a resonance wavelength shift $\Delta \lambda$.

Figure 2

Typical silicon-on-insulator waveguide geometries for optical biosensing.

Figure 3

Simulation of the normalized E-field intensity for the first TE- and TM-mode for a strip and slot waveguide. Reproduced from Ref. [38] (CC BY 4.0).

Figure 4

Schematics of different ring resonator concepts: (a) Common silicon strip-waveguide ring resonator. (b) Fully slotted ring resonator with a strip-waveguide as bus waveguide. (c) Hybrid-waveguide ring resonator consisting of a slot- and strip waveguide. The strip-to-slot optical mode transition is achieved by a slow-varying waveguide taper. (© 2018 IEEE. Reprinted, with permission, from Ref. [14]).

Figure 5

Representative example for surface functionalization. (A) Silicon surface of an activated SOI ring resonator. (B) In order to generate an amino-terminated surface, APTES is reacting with the surface siloxane groups. (C) Afterwards, S-HyNic is reacting with primary amines to build a HyNic-displaying surface. (D) Finally, the addition of 4FB-modified antibodies leads to a hydrazone bond formation between the 4FB moieties on the antibodies and the HyNic moieties on the surface. Reprinted (adapted) with permission from Ref. [72]. Copyright (2018) American Chemical Society.

Figure 6

(a) The antibody receptors are usually randomly oriented on the silicon surface when they are directly immobilized using physical adsorption. (b) Using a protein A layer leads to properly oriented antibody receptors. Reproduced from Ref. [61] (CC BY 4.0).

Figure 7

Schematic of typical measurement set-ups in laboratories. (a) The light source consists of an external cavity laser, which can tune its wavelength (tunable laser). In this case, a photodiode can be used as detector. (b) If a broad band light source (e.g., superluminescent diode) is employed, an optical spectrum analyzer is needed on the detector side.

Figure 8

Schematic of ring resonator array. Each ring is separately addressed in the electronic regime to individually measure the transmission. The sinusoidal input signal is divided in certain time slots. Adopted from Ref. [85].