Integrating Whispering Gallery Mode Refractive Index Sensing with Capillary Electrophoresis Separations Using Phase...

Area of Science:

• Optics and Photonics
• Analytical Chemistry
• Chemical Engineering

Background:

• Whispering gallery mode (WGM) resonators are dielectric structures that confine light via total internal reflection, exhibiting high-Q resonances sensitive to refractive index changes.
• WGM resonators excel in surface binding detection but struggle with bulk refractive index changes, limiting applications like capillary electrophoresis (CE).
• Capillary electrophoresis benefits from WGM's compact size and sensitivity for nondestructive, universal detection, but improved detection limits are needed.

Purpose of the Study:

• To develop a novel detection scheme for WGM resonators to enhance sensitivity for bulk refractive index sensing.
• To integrate WGM detection with capillary electrophoresis (CE) for improved analytical performance.
• To demonstrate the capability of the new method for real-time monitoring and separation analysis.

Main Methods:

• Development of phase sensitive WGM (PS-WGM) detection to monitor real-time shifts in the WGM spectrum.
• Direct comparison of PS-WGM detection with conventional spectral measurements for tracking WGM shifts.
• Integration of PS-WGM detection with capillary electrophoresis (CE) for analyzing separated analytes.

Main Results:

• PS-WGM detection achieved an improvement in detection limits by nearly 300-fold compared to standard spectral measurements.
• The integrated CE with PS-WGM system successfully demonstrated the separation of a three-component cation mixture (Na(+), Li(+), and K(+)).
• Real-time monitoring of refractive index shifts was achieved with enhanced sensitivity.

Conclusions:

• Phase sensitive WGM detection significantly enhances the sensitivity of WGM resonators for bulk refractive index sensing.
• The integration of CE with PS-WGM detection offers a powerful tool for sensitive, label-free analysis and separation.
• This advancement opens new possibilities for WGM resonators in demanding analytical applications like CE.