Aim: A requirement for nanoparticle (NP) research is visualization of particles within cells and tissues. Limitations of electron microscopy and low yields of NP fluorescent tagging warrant the identification of alternative imaging techniques. Method: Confocal reflectance microscopy (CRM) in combination with fluorescence imaging was assessed for visualizing rhodamine B-conjugated silver and fluorescein isothiocyanate-conjugated lipid core-stearylamine NP uptake in vitro and in vivo. Results: CRM successfully identified cellular uptake and blood-brain barrier penetration of NPs owing to their distinguishing refractive indices. NP-dependent reflectance signals in vitro were dose and incubation time dependent. Finally, CRM facilitated the distinction between nonspecific fluorescence signals and NPs. Conclusion: These findings demonstrate the value of CRM for NP visualization in tissues, which can be performed with a standard confocal microscope.
Keywords: brain; confocal; fluorescence; glioblastoma; lipid; metal; nanoparticles; reflectance; silver; stearylamine.
Nanoparticles (NPs) are extremely small materials utilized in the healthcare sector mainly for the delivery of drugs into tissues that are not easily accessible with regular pharmaceuticals. One such tissue is the brain, which has a barrier between it and the bloodstream that prevents the passage of most drugs. For NP research, the successful entry of NPs into target tissues must be demonstrated, but this is complicated by the small size and weak labeling of NPs. In this article, the authors demonstrate a low-cost, complementary microscopy technique that is readily available in most biological research laboratories and that can be used to detect and analyze the entry of different NP types into brain tissue and their uptake by brain tumor cells. These data create new opportunities for research on NP-assisted drug delivery to the central nervous system.