Caged-Sphere Optofluidic Sensors: Whispering Gallery Resonators in Wicking Microfluidics

Area of Science:

• Optofluidics
• Microsphere Resonators
• Biosensing

Background:

• Optofluidic technologies require user-friendly, sensitive sensing platforms for real-time liquid monitoring.
• Existing methods often involve complex sample manipulation and light coupling techniques.

Purpose of the Study:

• To demonstrate an integrated optofluidic sensor for simple, real-time liquid monitoring.
• To showcase the potential of open microfluidic chips combined with active dye-doped microspheres.

Main Methods:

• An open microfluidic chip with a pillar array was designed for passive liquid flow via evaporation.
• Active dye-doped whispering gallery mode microspheres were integrated, eliminating the need for fiber tapers.
• The sensor's performance was evaluated using varying concentrations of glucose solutions.

Main Results:

• The integrated optofluidic sensor demonstrated dynamic and reversible responses to glucose solutions.
• A refractive index sensitivity of approximately 40 nm/RIU was achieved with Q-factors of ~5 × 10^3.
• A detection limit of ~3 × 10^-3 RIU (~20 mg/mL glucose) was determined.

Conclusions:

• The developed optofluidic sensor offers a promising platform for point-of-care diagnostics.
• Further improvements in microsphere quality factor or lasing could enhance detection limits.
• The system's ease-of-use and passive flow capabilities facilitate simple real-time liquid analysis.