Low-frequency Raman spectroscopy has emerged as a powerful technique for investigating the vibrational dynamics of inorganic nanoparticles. These nanostructures support confined acoustic modes whose frequencies are governed by their size, shape, and composition. As such, low-frequency Raman measurements enable rapid, non-destructive characterization of nanoparticles, whether embedded in solid matrices or dispersed making it a valuable tool in nanomaterials science.

Colloidal nanoparticles are particularly appealing for applications in nanophononics due to the precise control they offer over size, morphology, and composition. [1]  In this context, surface ligands not only guide self-assembly but also influence the vibrational properties of the nanoparticles. This sensitivity of the acoustic vibration modes to surface modifications opens the door to using nanoparticles as sensitive “nanoresonators” probes for detecting and quantifying ligand adsorption.

In this work, we demonstrate how colloidal semiconductor nanoplatelets with precisely controlled thicknesses can serve as vibrational probes for monitoring surface chemistry via low-frequency Raman spectroscopy. We show that, beyond the simple “mass loading” effect of ligands, surface functionalization can induce notable structural modifications at the nanoscale, which are detectable through changes in vibrational spectra. [2] These findings are crucial for the accurate calibration of such nanoresonators when deployed as chemical or biological sensors.

In the second part, we examine the potential of nanoparticle-based vibrational probes for investigating chemical processes at interfaces. In particular, we present measurements related to the detection and monitoring of protein binding events, which suggest that low-frequency Raman scattering may be used as a label-free approach for probing biochemical interactions at the nanoscale.

[1] – Jansen, M., Tisdale, W.A. & Wood, V. Nanocrystal phononics. Nat. Mater. 22, 161–169 (2023). https://doi.org/10.1038/s41563-022-01438-4

[2] – Martinet, Q. et al. . Ligand-dependent nano-mechanical properties of CdSe nanoplatelets: calibrating nanobalances for ligand affinity monitoring. Nanoscale,13, 8639-8647 (2021). https://doi.org/10.1039/D1NR00270H