Accurate Quantification and Imaging of Cellular Uptake Using Single-Particle Surface-Enhanced Raman Scattering.

Understanding the uptake, distribution, and stability of gold nanoparticles (NPs) in cells is of fundamental importance in nanoparticle sensors and therapeutic development. Single nanoparticle imaging with surface-enhanced Raman spectroscopy (SERS) measurements in cells is complicated by aggregation-dependent SERS signals, particle inhomogeneity, and limited single-particle brightness. In this work, we assess the single-particle SERS signals of various gold nanoparticle shapes and the role of silica encapsulation on SERS signals to develop a quantitative probe for single-particle level Raman imaging in living cells. We observe that silica-encapsulated gap-enhanced Raman tags (GERTs) provide an optimized probe that can be quantifiable per voxel in SERS maps of cells. This approach is validated by single-particle inductively coupled mass spectrometry (spICP-MS) measurements of NPs in cell lysate post-imaging. spICP-MS also provides a means of measuring the tag stability. This analytical approach can be used not only to quantitatively assess nanoparticle uptake on the cellular level (as in previous digital SERS methods) but also to reliably image the subcellular distribution and to assess the stability of NPs in cells.