Surface plasmon polariton-enhanced upconversion luminescence for biosensing applications

Area of Science:

• Nanotechnology and Materials Science
• Biomedical Engineering
• Photonics and Optics

Background:

• Upconversion luminescence (UCL) offers high sensitivity for biosensing due to unique wavelength shifts.
• Low quantum efficiency is a primary limitation of UCL, often requiring high excitation power or sensitive detectors.
• Surface plasmon polaritons (SPPs) are known to enhance light-matter interactions.

Purpose of the Study:

• To demonstrate and investigate SPP-enhanced UCL for improved biosensing performance.
• To enhance the quantum efficiency of upconverting nanoparticles (UCNPs) using SPP coupling.
• To enable UCL-based assays with reduced excitation intensity requirements.

Main Methods:

• Fabrication of a gold grating to excite surface plasmon polaritons (SPPs).
• Optimization of the gold grating to match SPP resonance with UCNP absorption wavelengths.
• Immobilization of antibody-conjugated UCNPs onto the fabricated gold grating surface.
• Experimental measurement and computational simulation of UCL enhancement.

Main Results:

• Achieved up to a 65-fold enhancement in UCL intensity at low excitation power density.
• Demonstrated that SPP coupling increases the absorption cross-section of UCNPs.
• Computational analysis revealed a minor quenching effect near gold surfaces, consistent with experimental data.

Conclusions:

• SPP enhancement is an effective strategy to overcome the low quantum efficiency of UCNPs for biosensing.
• The developed method allows for highly sensitive UCL biosensing with significantly reduced excitation power.
• This approach is promising for applications requiring low excitation intensity, such as scanning-free imaging.