Flexible Microsphere-Embedded Film for Microsphere-Enhanced Raman Spectroscopy

Area of Science:

• Optics and Photonics
• Spectroscopy
• Materials Science

Background:

• Dielectric microspheres exhibit unique optical properties like photonic nanojets and whispering-gallery modes (WGMs).
• Microsphere-enhanced Raman spectroscopy (MERS) leverages these properties for enhanced molecular detection.
• Fabricating stable microsphere monolayer arrays on diverse surfaces remains a key challenge for MERS practical application.

Purpose of the Study:

• To develop a flexible and adaptable MERS sensing platform for various specimen surfaces.
• To investigate the Raman enhancement mechanisms in the proposed platform.
• To improve the limit of detection for ultrasensitive molecular sensing.

Main Methods:

• Fabrication of a microsphere-embedded film (MF) by immersing a microsphere monolayer array in a poly(dimethylsiloxane) (PDMS) film.
• Characterization of the MF platform for its optical properties and Raman enhancement capabilities.
• Integration of MF with surface-enhanced Raman spectroscopy (SERS) and development of a hybrid dual-layer enhancer.

Main Results:

• The MF platform demonstrated significant Raman enhancement, primarily attributed to directional antennas and wave-guided WGMs (WG-WGMs).
• Coupling MF with SERS resulted in over a 10-fold enhancement, improving the detection limit for crystal violet and Sudan I to 10^-7 M.
• A hybrid dual-layer microsphere enhancer achieved over a 50-fold enhancement ratio, with WG-WGMs becoming dominant.

Conclusions:

• The microsphere-embedded film offers a flexible and cost-effective MERS sensing platform for 1D to 3D surfaces.
• The developed platform, especially in its hybrid dual-layer configuration, significantly enhances Raman detection sensitivity.
• This work presents new avenues for designing advanced MERS and SERS techniques for ultrasensitive molecular analysis.