In Depth Mapping of Mesoporous Silica Nanoparticles in Malignant Glioma Cells Using Scattering-Type Scanning Near-Field Optical Microscopy

Abstract

Mesoporous silica nanoparticles (MSNPs) are promising nanomedicine vehicles due to their biocompatibility and ability to carry large cargoes. It is critical in nanomedicine development to be able to map their uptake in cells, including distinguishing surface associated MSNPs from those that are embedded or internalized into cells. Conventional nanoscale imaging techniques, such as electron and fluorescence microscopies, however, generally require the use of stains and labels to image both the biological material and the nanomedicines, which can interfere with the biological processes at play. We demonstrate an alternative imaging technique for investigating the interactions between cells and nanostructures, scattering-type scanning near-field optical microscopy (s-SNOM). s-SNOM combines the chemical sensitivity of infrared spectroscopy with the nanoscale spatial resolving power of scanning probe microscopy. We use the technique to chemically map the uptake of MSNPs in whole human glioblastoma cells and show that the simultaneously acquired topographical information can provide the embedding status of the MSNPs. We focus our imaging efforts on the lamellipodia and filopodia structures at the peripheries of the cells due to their significance in cancer invasiveness.

Figure 1

s-SNOM imaging of mesoporous silica nanoparticles (MSNPs). (a, b) TEM images of MSNPs. (c) FTIR absorption spectra of MSNPs (blue curve) and untreated U-87 MG cells (red curve). (d, e) s-SNOM images of MSNPs on a mica substrate acquired at 1100 and 1300 cm^–1, respectively. Scale bars 100 nm.

Figure 2

s-SNOM imaging of U-87 MG cells. (a) AFM topography of a region at the periphery of a U-87 MG cell. (b) s-SNOM image of the same region acquired at an imaging wavelength of 1667 cm^–1. (c) Corresponding region imaged with the built-in microscope in the s-SNOM system (cropped from the full image shown in Supplementary Figure SI2). (d) Correlation between the s-SNOM phase and the sample height was obtained using the values at each pixel in the images. The cell and the substrate were split into groups by masking images. Fp, filopodia; Lp, lamellipodium. Scale bars 2 μm (a, b), 5 μm (c).

Figure 3

s-SNOM imaging of mesoporous silica nanoparticles (MSNPs) in U-87 MG cells. (a, b) s-SNOM (a, 1100 cm^–1) and AFM (b) images of an MSNP-treated air-dried U-87 MG cell. (c) Insets (i–iv), MSNP interaction with lamellopodia and filopodia, enlarged from (a), acquired at 1100 or 1300 cm^–1, and AFM images of the same regions.

Figure 4

Correlating phase and topography profiles of mesoporous silica nanoparticles (MSNPs) in U-87 MG cells. (a–d) s-SNOM (a, c; 1100 cm^–1) and AFM (b, d) images of an MSNP-treated air-dried U-87 MG cell. (e) s-SNOM phase and topography profiles of three MSNPs interacting with the U-87 MG cell. MSNPs (spheres of d ∼ 80 nm) are shown for reference. Scale bars 200 nm.