Proceedings Article | 5 October 2023
KEYWORDS: Raman spectroscopy, Chemical analysis, Biological research, Biological imaging, Spatial resolution, Scanning tunneling microscopy, Monolayers, Atomic force microscopy, Imaging spectroscopy, Hyperspectral imaging
Lack of analytical tools capable of providing nanoscale chemical characterization of biomembranes under ambient conditions in a non-invasive and label-free fashion limits our understanding of the vital cellular processes. Tip-enhanced Raman spectroscopy (TERS) is one of the very few analytical techniques capable of meeting this challenge by combining the single-molecule sensitivity of surface-enhanced Raman spectroscopy and nanoscale spatial resolution of scanning probe microscopy [1, 2]. In this talk, I will discuss how TERS can be applied in both atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) modes for correlative topographical and chemical analysis of biological membranes at the nanoscale. Specifically, I will present some recent studies from our laboratory to demonstrate the application of hyperspectral TERS imaging for nanoscale visualization of molecular disorder in supported lipid membranes [3], phase separation in mixed lipid (DPPC, DOPC and cholesterol) membranes and molecular complexity of a human cell membrane [4]. For example, in a Au(111) supported DPPC monolayer sample, we achieved reproducible STM-TERS imaging together with the correlative topography imaging for the first time. Furthermore, TERS images revealed the presence of structural defects in the DPPC monolayer and ratiometric analysis of the C-H stretching region revealed domains of high and low molecular disorder with ca. 20 nm spatial resolution. We went a step further and investigated the molecular complexity of a real-life human cell membrane using TERS. Hyperspectral AFM TERS imaging showed segregation of nanoscale phenylalanine, histidine, phosphatidylcholine, protein, and cholesterol-rich domains in a pancreatic cancer cell membrane ca. 20 nm spatial resolution. These results demonstrate the unique ability of TERS to provide label-free and non-destructive characterization of biomembranes with nanoscale resolution under ambient conditions.
References
[1]Kumar, N., Mignuzzi, S., Su, W., Roy D., Tip-enhanced Raman spectroscopy: Principles and applications. European Physical Journal Techniques and Instrumentation 2015, 2(1), 9.
[2] Kumar, N., et al., Nanoscale mapping of newly-synthesised phospholipid molecules in a biological cell using tip-enhanced Raman spectroscopy. Chemical Communications, 2017, 53 (16), 2451-2454.
[3] Pandey, Y., Kumar, N., Goubert, G., Zenobi, R., Nanoscale Chemical Imaging of Supported Lipid Monolayers using Tip‐Enhanced Raman Spectroscopy. Angewandte Chemie. 2021, 133, 19189-19194.
[4] Mrđenović, D., Ge, W., Kumar, N., Zenobi, R., Nanoscale Chemical Imaging of Human Cell Membranes Using Tip-Enhanced Raman Spectroscopy. Angewandte Chemie International Edition, 2022, 61, e2022102.
