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Characterizing Individual Protein Aggregates by Infrared Nanospectroscopy and Atomic Force Microscopy
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Sub-Tip-Radius Near-Field Interactions in Nano-FTIR Vibrational Spectroscopy on Single Proteins
Jun Nishida1,2, Akihiro Otomo1,2, Takanori Koitaya1
1Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Aichi 444-8585, Japan.
Nano Letters
|January 9, 2024
Summary
Tip-enhanced infrared spectroscopy now probes single proteins at the nanoscale. Utilizing higher harmonic detection in nano-FTIR enhances vibrational resonance signals for subnanoscale chemical analysis.
Area of Science:
- Tip-enhanced vibrational spectroscopy
- Nanoscale chemical analysis
- Near-field interactions
Background:
- Tip-enhanced Raman spectroscopy achieves atomic-scale sensitivity.
- Tip-enhanced infrared spectroscopy (nano-FTIR, AFM-IR) enables nanoscale chemical analysis.
- Fundamental limits in infrared nanospectroscopy resolution and sensitivity require understanding near-field interactions.
Purpose of the Study:
- To quantitatively understand near-field interactions in infrared nanocavities.
- To demonstrate nano-FTIR spectroscopy for probing single protein vibrations.
- To explore enhanced spatial resolution and sensitivity in infrared nanospectroscopy.
Main Methods:
- Application of nano-FTIR spectroscopy.
- Probing the amide-I vibration of a single protein (∼500 amino acid residues).
- Utilizing higher tip tapping demodulation harmonics (up to the seventh order).
Main Results:
- Pronounced enhancement in vibrational resonance peak amplitude observed.
- Signal enhancement attributed to sub-tip-radius geometrical effects beyond dipole approximations.
- Quantitative characterization of single-nanometer near-field interactions achieved.
Conclusions:
- Nano-FTIR spectroscopy can probe single proteins at the nanoscale.
- Higher harmonic detection significantly enhances vibrational resonance signals.
- This work paves the way for subnanoscale and single-molecule infrared vibrational spectroscopy.
