Broadband optical absorbance spectroscopy using a whispering gallery mode microsphere resonator

Area of Science:

• Optical Physics
• Nanotechnology
• Analytical Chemistry

Background:

• Whispering gallery modes (WGMs) in microsphere resonators are sensitive to their environment.
• Previous WGM sensors typically use single modes for limited measurements.
• Broadband absorbance measurements offer enhanced sensing capabilities.

Purpose of the Study:

• To develop a broadband optical absorbance measurement technique using multiple WGMs.
• To utilize a microfluidic channel integrated with a microsphere resonator for sensing.
• To investigate the interaction of analytes with functionalized microsphere surfaces.

Main Methods:

• Simultaneous excitation and monitoring of multiple WGMs in a microsphere resonator.
• Coupling WGMs using a hemispherical prism sealing a microfluidic channel.
• Measuring changes in transmission of precessed modes due to analyte absorbance.
• Functionalizing microsphere surfaces with organosilanes (octadecyl, amino, fluoro groups).

Main Results:

• Successful broadband optical absorbance measurements of dyes, aromatic, and biological molecules.
• Demonstrated interaction of analytes with functionalized surfaces via electrostatic and hydrophobic forces.
• Achieved repeatable pathlength measurements within a few percent.
• Observed significant pathlengths (several centimeters) for methylene blue dye indicating strong surface interaction.

Conclusions:

• The developed method enables sensitive, broadband absorbance measurements using multiple WGMs.
• Surface functionalization of microspheres allows for tailored analyte detection through specific interactions.
• This approach holds promise for high-sensitivity detection in microfluidic sensing applications.