Freeze-frame approach for robust single-molecule tip-enhnaced Raman spectroscopy at room temperature

TL;DR

This paper introduces a freeze-frame method using a thin Al2O3 layer to enable robust, room-temperature single-molecule TERS imaging of BCB, revealing conformational heterogeneity through spectral analysis and DFT calculations.

Contribution

The study presents a novel freeze-frame approach with an Al2O3 capping layer that stabilizes single-molecule TERS measurements at room temperature, allowing for reliable chemical imaging and spectral analysis.

Findings

Successful hyperspectral TERS imaging of single molecules at room temperature.

Observation of Raman peak variations up to 7.5 cm-1 at the single-molecule level.

Revealed conformational heterogeneity through DFT-based spectral analysis.

Abstract

A quantitative single-molecule tip-enhanced Raman spectroscopy (TERS) study at room temperature remained a challenge due to the rapid structural dynamics of molecules exposed to air. Here, we demonstrate the single-molecule level hyperspectral TERS imaging of brilliant cresyl blue (BCB) at room temperature for the first time, along with quantitative spectral analyses. Freeze-frame approach using a thin Al2O3 capping layer, which suppresses spectral diffusions and inhibits chemical reactions and contaminations in air, enabled reliable and robust chemical imaging. For the molecules resolved spatially in the TERS image, a clear Raman peak variation up to 7.5 cm-1 is observed, which cannot be found in molecular ensembles. From density functional theory-based quantitative analyses of the varied TERS peaks, we reveal the conformational heterogeneity at the single-molecule level. This work provides a facile way to investigate the single-molecule properties in interacting media, expanding the scope of single-molecule vibrational spectroscopy.