Label-free separation of human embryonic stem cells and their cardiac derivatives using Raman spectroscopy

Self-renewable, pluripotent human embryonic stem cells (hESCs) can be differentiated into cardiomyocytes (CMs), providing an unlimited source of cells for transplantation therapies. However, unlike certain cell lineages such as hematopoietic cells, CMs lack specific surface markers for convenient identification, physical separation, and enrichment. Identification by immunostaining of cardiac-specific proteins such as troponin requires permeabilization, which renders the cells unviable and nonrecoverable. Ectopic expression of a reporter protein under the transcriptional control of a heart-specific promoter for identifying hESC-derived CMs (hESC-CMs) is useful for research but complicates potential clinical applications. The practical detection and removal of undifferentiated hESCs in a graft, which may lead to tumors, is also critical. Here, we demonstrate a nondestructive, label-free optical method based on Raman scattering to interrogate the intrinsic biochemical signatures of individual hESCs and their cardiac derivatives, allowing cells to be identified and classified. By combination of the Raman spectroscopic data with multivariate statistical analysis, our results indicate that hESCs, human fetal left ventricular CMs, and hESC-CMs can be identified by their intrinsic biochemical characteristics with an accuracy of 96%, 98%, and 66%, respectively. The present study lays the groundwork for developing a systematic and automated method for the noninvasive and label-free sorting of (i) high-quality hESCs for expansion and (ii) ex vivo CMs (derived from embryonic or adult stem cells) for cell-based heart therapies.