SERS of molecules that do not adsorb on Ag surfaces: a metal-organic framework-based functionalization strategy

Area of Science:

• Analytical Chemistry
• Materials Science
• Nanotechnology

Background:

• Surface-enhanced Raman scattering (SERS) offers unique vibrational signatures for chemical detection.
• Detecting weakly adsorbing molecules on non-functionalized plasmonic materials via SERS is challenging.
• Metal-organic frameworks (MOFs) can be utilized for molecular adsorption and pre-concentration.

Purpose of the Study:

• To develop an improved SERS-based detection method for volatile organic compounds (VOCs).
• To utilize a polycrystalline MOF film to recruit and concentrate analytes for SERS detection.
• To overcome the limitations of weak analyte adsorption on conventional SERS substrates.

Main Methods:

• Grew polycrystalline MOF films on silver "films-over-nanospheres" (FONs) substrates.
• Exposed MOF-coated FONs to various aromatic VOCs (benzene, toluene, nitrobenzene, 2,6-di-tert-butylpyridine).
• Analyzed SERS spectra of adsorbed analytes and performed concentration and time-resolved measurements.

Main Results:

• MOF films effectively trapped and concentrated target VOCs at the FON surface.
• Unique SERS spectra of benzene, toluene, nitrobenzene, and 2,6-di-tert-butylpyridine were successfully recorded.
• Analyte adsorption was found to be reversible, occurring at MOF nanocrystal grain boundaries.

Conclusions:

• The MOF-coated FON approach enables SERS detection of weakly adsorbing aromatic molecules.
• This method overcomes limitations of conventional SERS substrates for such analytes.
• The developed technique offers a generalized strategy for confining aromatic molecules for SERS sensing applications.