Nanoscale infrared absorption imaging permits non-destructive intracellular photosensitizer localization for subcellular uptake analysis

The most immediate biological and medical advantages of therapeutic agent localization on the nanoscale arise from the increased understanding of targeted delivery, selectivity and intracellular distribution that are gained by imaging at the resolution scale of individual nanovectors and therapeutic agents themselves. This paper reports on the use of a nanoscale resolution chemical imaging method, infrared (IR) nanospectral absorption imaging, used to map the subcellular localization of a photoactive therapeutic agent - toluidine blue-conjugated gold nanoparticles (TBO) within nanoscale subsections of single colon adenocarcinoma cells. By comparison of photosensitizer distribution with diffraction limited optical imaging, the benefits of IR nanospectral localization are highlighted and the spatial and spectral accuracy of the non-destructive IR imaging method is confirmed. IR spectral ratio imaging is presented as a means to map intracellular nanoparticle density at sub 50 nm lateral resolution with IR nanospectroscopy enabling distinction of nanoparticle seeded cells from a control group with 95% confidence. In this way we illustrate that IR absorption nanoimaging combined with IR point source data does not only yield intracellular drug detection on the order of nanometres, but also permits extension of the AFM-IR technique from subcellular analysis up to studies of cell numbers that are statistically significant.