SERS Imaging of Mesenchymal Stromal Cell Differentiation

Abstract

Understanding the process of mesenchymal stromal cell (MSC) osteogenic differentiation is essential for a wide range of medical applications. However, these primary cells vary significantly from donor to donor, making it difficult to fully exploit their therapeutic potential. Although osteogenic differentiation has been studied extensively, there is still a shortage of standardized methods for the evaluation of the degree of differentiation. Here, we employ noninvasive surface-enhanced Raman scattering (SERS) for studying such cells, offering a better understanding of cellular processes in situ. We present the long-term differentiation of MSCs on biocompatible gold nanoisland SERS substrates, combining imaging of cells with spectroscopic detection of molecular species and chemical events occurring on the cellular membrane adjacent to the surface of the SERS substrate. We detect multiple signs of bone tissue formation, from an early stage to mature osteoblasts, without labeling. We show that the results correlate very well with classical differentiation-detecting assays, indicating that the SERS imaging technique alone is sufficient to study the progress of osteogenic differentiation of such cells, paving a way toward continuous label-free screening of live cells.

Surface enhanced Raman scattering for probing cellular biochemistry

“…On gold nanoisland decorated cover glasses, relevant features from the lipid bilayer structure can be studied in spite of the inherently low Raman cross section of lipids. [60][61][62] By probing the polar heads and the acyl chains of the lipids in the membrane outer leaflet, specific lipid/lipid interactions and membrane properties can be distinguished. As examples, regions of higher or lower degrees of order of the lipid acyl chains are evidenced by the presence of specific C-C stretching frequencies in the spectra from different membrane regions (see Figure 2), in agreement with known differences in the fluidity of the plasma membrane at different positions.…”

“…While SERS of intracellular compartments requires the incorporation, either actively or passively, of SERS substrates into the cells, the plasma membrane can be brought easily into the proximity of plasmonic nanostructures. [59][60][61][62] The selective probing of membrane proteins and ligand-receptor binding events at the plasma membrane level is usually assessed by fluorescence microscopy or other related techniques, but several recent examples show that SERS probing can provide a lot of additional chemical information without the addition of label molecules.…”

Recent Advances in Monitoring Stem Cell Status and Differentiation Using Nano-Biosensing Technologies

“…There are two SERS strategies—labeled and label-free methods for detection with and without biomarkers, respectively. The label-free SERS method provides rich stem cell information for identification without labeling the analytes [ 186 , 187 , 188 , 189 , 190 , 191 , 192 ]. In this method, the information of the biomacromolecules, such as the protein structure, nutrient amounts, and biological processes occurring at the cellular level that change during differentiation, can be detected.…”

“…In this method, the information of the biomacromolecules, such as the protein structure, nutrient amounts, and biological processes occurring at the cellular level that change during differentiation, can be detected. Milewska et al [ 189 , 192 ] reported on the differentiation of BM-MSCs using label-free SERS. They examined the bands of cholesterol, proteins, collagen backbone, proline, calcium hydroxyapatite, and a phospholipid alkyl chain for SERS mapping ( Figure 5 ) [ 192 ].…”

“…Milewska et al [ 189 , 192 ] reported on the differentiation of BM-MSCs using label-free SERS. They examined the bands of cholesterol, proteins, collagen backbone, proline, calcium hydroxyapatite, and a phospholipid alkyl chain for SERS mapping ( Figure 5 ) [ 192 ]. BM-MSCs cultured on a biocompatible nanostructured gold substrate for 7 and 21 days revealed different stages of the differentiation spectrum of individual cells, such as molecular species and chemical events on the cellular membrane [ 189 , 192 ].…”