Methods capable of nondestructively collecting high-quality, real-time chemical information from living human stem cells are of increasing importance given the escalating relevance of stem cells in therapeutic and regenerative medicines. Raman spectroscopy is one such technique that can nondestructively collect real-time chemical information. Living cells uptake gold nanoparticles and transport these particles through an endosomal pathway. Once inside the endosome, nanoparticles aggregate into clusters that give rise to large spectroscopic enhancements that can be used to elucidate local chemical environments through the use of surface-enhanced Raman spectroscopy. This report uses 40-nm colloidal gold nanoparticles to create volumes of surface-enhanced Raman scattering (SERS) within living human-adipose-derived adult stem cells enabling molecular information to be monitored. We exploit this method to spectroscopically observe chemical changes that occur during the adipogenic differentiation of human-adipose-derived stem cells over a period of 22 days. It is shown that intracellular SERS is able to detect the production of lipids as little as one day after the onset of adipogenesis and that a complex interplay between lipids, proteins, and chemical messengers can be observed shortly thereafter. After 22 days of differentiation, the cells show visible and spectroscopic indications of completed adipogenesis yet still share spectral features common to the progenitor stem cells.

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