Observing Single Molecules Complexing with Cucurbit[7]uril through Nanogap Surface-Enhanced Raman Spectroscopy.

Area of Science:

• Supramolecular Chemistry
• Spectroscopy
• Nanotechnology

Background:

• Surface-enhanced Raman spectroscopy (SERS) offers single-molecule sensitivity.
• Supramolecular host-guest chemistry involves interactions within molecular cages.
• Cucurbit[7]uril is a macrocyclic host with a well-defined cavity.

Purpose of the Study:

• To investigate host-guest interactions of cucurbit[7]uril at the single-molecule level.
• To utilize SERS for probing structural changes in cucurbit[7]uril upon guest inclusion.
• To explore anisotropic intermolecular interactions between guests and the host molecule.

Main Methods:

• Employing a nanogap geometry with gold nanoparticles on a gold surface for intense SERS signals.
• Achieving single-molecule sensitivity using a modified bianalyte method.
• Analyzing changes in Raman modes of cucurbit[7]uril to detect guest-induced structural alterations.

Main Results:

• Observed distinct changes in cucurbit[7]uril's Raman modes when single guests were encapsulated.
• Demonstrated that encapsulated guests cause internal stretching of the host molecule.
• Identified anisotropic intermolecular interactions between guests and the host, leading to unique Raman spectral features.

Conclusions:

• Single-molecule SERS is effective for studying supramolecular host-guest systems.
• Guest molecules induce measurable structural changes and anisotropic interactions within cucurbit[7]uril.
• This technique provides detailed insights into molecular recognition and binding at the single-molecule level.