Abstract
Identification of tumor and normal cells is a promising application of Raman spectroscopy. The throughput of Raman-assisted cell sorting is limited by low sensitivity. Surface-enhanced Raman spectroscopy (SERS) is a well-recognized candidate to increase the intensity of Raman signals of cells. First, different strategies are summarized to detect tumor cells using targeted SERS probes. Then, a protocol is described to prepare multicore-SERS-labels (MSLs) by aggregating gold nanoparticles, coating with a reporter molecule and a thin silver shell to further boost enhancement, encapsulating with a stable silica layer, and functionalizing by epithelial cell adhesion molecule (EpCAM) antibodies. Raman, dark field and fluorescence microscopy proved the specific and nonspecific binding of functionalized and nonfunctionalized MSLs to MCF-7 tumor cells, leukocytes from blood, and nontransformed human foreskin fibroblasts. Raman imaging and dark field microscopy indicated no uptake of MSLs, yet binding to the cellular membrane. Viability tests were performed with living tumor cells to demonstrate the low toxicity of MSL-EpCAM. The SERS signatures were detected from cells with exposure times down to 25 ms at 785-nm laser excitation. The prospects of these MSLs in multiplex assays, for enumeration and sorting of circulating tumor cells in microfluidic chips, are discussed.