• surface-enhanced Raman scattering;
  • live cell;
  • pH monitoring;
  • drug diffusion


The local pH inside individual live glioma (U-87 MG) cancer cells was monitored after treatment by the photodynamic therapy drug 6-methyl-1,3,8-trihydroxyanthraquinone (emodin). The cellular pH is tracked by the real-time measurement of the surface-enhanced Raman scattering (SERS) from a probe that is embedded in the cell. The probe is a micrometer-sized silica bead that is covered by nanosized silver colloids, which enhance Raman signal, and 4-mercaptobenzoic acid (pMBA) whose molecular vibrations and resulting Raman spectrum are sensitive to pH. Visible excitation at different light dosages is used to activate the drug. The results indicate cell maintenance of internal pH and cell death at low and high light dosage, respectively. We demonstrate that these SERS probes are an effective tool for ex vivo pH monitoring in a live cell thanks to their high optical sensitivity and noninvasive usage. Copyright © 2011 John Wiley & Sons, Ltd.