Portable microresonator-based label-free detector: monotonous resonance splitting with particle adsorption

Area of Science:

• Photonics and sensing technologies
• Nanotechnology and materials science
• Biomedical engineering and diagnostics

Background:

• Whispering gallery mode (WGM) resonators offer high sensitivity for detection applications, particularly as biosensors.
• Current WGM resonator systems require expensive and bulky equipment, limiting their use to specialized laboratories.
• There is a need for simplified, cost-effective, and portable WGM-based detection systems.

Purpose of the Study:

• To propose and investigate a novel functionalization strategy for micro-ring resonators to enable self-heterodyne detection.
• To demonstrate a sensitive and robust detection scheme that can be monitored by conventional electronics.
• To pave the way for portable WGM-based detectors and point-of-care diagnostic tools.

Main Methods:

• A micro-ring resonator was designed and completely covered by a Bragg grating.
• Functionalization of the resonator was selectively applied to only a quarter of its perimeter.
• The frequency splitting of specific resonances near the band gap edge was monitored as target molecules bound to the functionalized region.

Main Results:

• Functionalization of a quarter perimeter of the Bragg-grating-covered micro-ring resonator induced monotonous frequency splitting of specific resonances.
• The observed frequency splitting was in the GHz range, detectable by conventional electronics.
• The ultrahigh sensitivity characteristic of WGM resonators was successfully maintained with the proposed method.

Conclusions:

• The proposed self-heterodyne detection scheme offers a robust and sensitive method for WGM resonator-based sensing.
• This approach eliminates the need for finely tunable lasers or spectrometers, simplifying the detection apparatus.
• The development holds significant potential for creating portable biosensors and point-of-care diagnostic devices.