Silicon Photonic Micro-Ring Resonators for Chemical and Biological Sensing: A Tutorial

Abstract

Silicon photonic micro-ring resonators (MRR) developed on the silicon-on-insulator (SOI) platform, owing to their high sensitivity and small footprint, show great potential for many chemical and biological sensing applications such as label-free detection in environmental monitoring, biomedical engineering, and food analysis. In this tutorial, we provide the theoretical background and give design guidelines for SOI-based MRR as well as examples of surface functionalization procedures for labelfree detection of molecules. After introducing the advantages and perspectives of MRR, fundamentals of MRR are described in detail, followed by an introduction to the fabrication methods, which are based on a complementary metal-oxide semiconductor (CMOS) technology. Optimization of MRR for chemical and biological sensing is provided, with special emphasis on the optimization of waveguide geometry. At this point, the difference between chemical bulk sensing and label-free surface sensing is explained, and definitions like waveguide sensitivity, ring sensitivity, overall sensitivity as well as the limit of detection (LoD) of MRR are introduced. Further, we show and explain chemical bulk sensing of sodium chloride (NaCl) in water and provide a recipe for label-free surface sensing.

Optimization of Surface Functionalizations for Ring Resonator-Based Biosensors

“…The functionalization strategy selected for the MRR surface is based on the covalent binding of aptamers through organosilanes exposing epoxy or mercapto groups. Organosilanes are often used to functionalize the MRR surface [20] due to the oxidized silicon surface of these sensors. However, the organosilanes generally used are the amino-and epoxy-silanes.…”

“…A large number of surface functionalization strategies do exist; some examples of such strategies are the physical adsorption by direct deposition of molecules, the covalent binding of molecular chemical groups to the sensor surface, and the non-covalent interactions with a deposited active layer [17]. Among the covalent binding of chemical groups, silanes are also widely used in the context of MRR [20]. This modification is based on the formation of covalent Si-O-Si bonds between the oxidized silicon structure and the coating substance, i.e., an organosilane with a chemical residue suitable for the binding of a specific recognition element.…”

“…This modification is based on the formation of covalent Si-O-Si bonds between the oxidized silicon structure and the coating substance, i.e., an organosilane with a chemical residue suitable for the binding of a specific recognition element. The most used silanes are aminoand epoxy-silanes [20], whereas here, a mercaptosilane was tested and compared to a more classical epoxysilane, showing much better performance.…”

Ultrasensitive Silicon Photonic Refractive Index Sensor Based on Hybrid Double Slot Subwavelength Grating Microring Resonator

“…The type of refractive index sensor based on silicon photonics is also a functional device that can resonate, interfere, and be absorbed by light waves, including microdisk resonator sensors [ 12 , 13 , 14 ], microring resonators (MRR) sensors [ 15 , 16 , 17 , 18 ], Mach-Zehnder interferometer (MZI) Sensors [ 19 , 20 , 21 ], multimode waveguide interference coupler sensors [ 22 , 23 ], photonic crystal cavities [ 24 , 25 ]. Or it could be a combination of MZI-MRR, MRR-MRR, and MZI-MZI, based on the Vernier effect that significantly increases sensitivity [ 26 , 27 , 28 , 29 ].…”

Surface Plasmon Resonance Imaging (SPRi) and Photonic Integrated Circuits (PIC) for COVID-19 Severity Monitoring

“…In this way, PIC-based biosensors can prescreen the patients in terms of COVID-19 severity to decide for a booster vaccination or further in-depth analysis using SPR imaging with multiplex targets as well as for the purpose of treatment and therapy of COVID-19 patients close to the point of care. PIC-based biosensors are intensively studied [3,4] and their sensitivity and limit of detection was improved over the last decade, reaching similar performance as SPR devices [5,6]. However, a widespread use as point-of-care device requires novel fabrication approaches to realize disposable COVID-19 tests [7].…”