Microscopic investigation of" topically applied nanoparticles for molecular imaging of fresh tissue surfaces.

Previous studies have shown that functionalized nanoparticles (NPs) topically applied on fresh tissues are able to rapidly target cell-surface protein biomarkers of cancer. Furthermore, studies have shown that a paired-agent approach, in which an untargeted NP is co-administered with a panel of targeted NPs, controls for the nonspecific behavior of the NPs, enabling quantitative imaging of biomarker expression. However, given the complexities in nonspecific accumulation, diffusion, and chemical binding of targeted NPs in tissues, studies are needed to better understand these processes at the microscopic scale. Here, fresh tissues were stained with a paired-agent approach, frozen, and sectioned to image the depth-dependent accumulation of targeted and untargeted NPs. The ratio of targeted-to-untargeted NP concentrations-a parameter used to distinguish between tumor and benign tissues-was found to diminish with increasing NP diffusion depths due to nonspecific accumulation and poor washout. It was then hypothesized and experimentally demonstrated that larger NPs would exhibit less diffusion below tissue surfaces, enabling higher targeted-to-untargeted NP ratios. In summary, these methods and investigations have enabled the design of NP agents with improved sensitivity and contrast for rapid molecular imaging of fresh tissues.