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

Abstract

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 postimaging. 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.

Comparison of Gap-Enhanced Raman Tags and Nanoparticle Aggregates with Polarization Dependent Super-Resolution Spectral SERS Imaging

“…This was verified by correlating the field of view in the SERS image to SEM images of the same area, where single bipyramids are observed (Figure S1) in the SEM images but not in the SERS images at any polarization direction. This indicates that the bipyramids used in this study cannot be detected as single particles, but dimers and larger aggregates can be detected, which is consistent with prior work. , Some of the bipyramids formed aggregates with spheres from the seed used to synthesize the bipyramids, which produced a strong polarization-dependent SERS signal, so this shape of the aggregate provides a comparison to the bipyramid-GERTs. Figure shows polarization dependent imaging of a representative bipyramid-sphere aggregate (denoted BPA for brevity) from the first half-rotation of the polarization.…”

“…An emerging class of nanostructures for SERS is gap-enhanced Raman tags (GERTs), where a reporter molecule, such as nitrothiophenol (NTP), is used as a shape directing agent to form size controlled nanogaps. , A variety of GERTs have since been reported, but tend to fall into two distinct categories: smooth-shell GERTs (S-GERTs) that have a smooth outer shell and petal-GERTs (P-GERTs) that consist of small petal-like structures that create a roughened outer layer . Generally, because of the large surface areas for molecules to adsorb and that the size of the gaps can be easily controlled, both types of GERTs have been shown to have consistent and reliable particle-to-particle SERS responses. − However, because the P-GERTs have more nanogaps and a larger surface area for more reporter molecules to be immobilized on the surface, both of which are dependent on the number and size of petals, they tend to have brighter, more consistent SERS intensity, up to 2 orders of magnitude. , P-GERTs and other spikey surfaced GERTs have mostly been limited to spherical or rod shaped cores . The electric field confinement of GERTs, particularly P-GERTs, is generally less understood relative to traditional aggregates due to the complexity and large amount of petals that make electromagnetic simulations difficult.…”