Analyte Co-localization at Electromagnetic Gap Hot-Spots for Highly Sensitive (Bio)molecular Detection by Plasmon...

Area of Science:

• Plasmonics
• Nanotechnology
• Spectroscopy

Background:

• Electromagnetic hot-spots in plasmonic nanogaps enhance sensitivity in surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy.
• Leveraging these hot-spots requires analyte access to nanogaps, dependent on analyte size relative to gap dimensions.

Purpose of the Study:

• To develop a method for creating uniform plasmonic nanopillar arrays with tunable sub-10 nm gaps.
• To investigate the impact of analyte dimensions versus gap size on hot-spot utilization and assay sensitivity.
• To compare SERS and metal-enhanced fluorescence for detecting analytes within confined plasmonic gaps.

Main Methods:

• Fabrication of high-density plasmonic nanopillar arrays using self-assembled block copolymer colloids on a full wafer.
• Systematic variation of interpillar gap distances.
• Detection of labeled proteins and small organic molecules using SERS and metal-enhanced fluorescence.

Main Results:

• Achieved high-density arrays (>10^10 cm^-2) with uniform interpillar hot-spots and tunable sub-10 nm gaps.
• Demonstrated trends showing analyte size relative to gap distance critically impacts hot-spot leverage and SERS sensitivity.
• Revealed advantages of fluorescence over Raman detection under spatial confinement, achieving picomolar detection limits for both small molecules and proteins.

Conclusions:

• Rational design of electromagnetic hot-spots, considering analyte dimensions, is crucial for achieving ultrahigh sensitivity in plasmon-enhanced spectroscopies.
• Well-defined nanopillar geometries enable accurate correlation between structure, optical properties, and sensitivity in plasmonic assays.
• The developed nanofabrication approach provides a platform for optimizing ultrasensitive molecular detection.