Increasing the Efficacy of Gold Nanorod Uptake in Stem Cell-Derived Therapeutic Cells: Implications for Stem Cell Labeling and Optical Coherence Tomography Imaging

The advancement of safe nanomaterials for use as optical coherence tomography (OCT) imaging and stem cell-labeling agents to longitudinally visually track therapeutic derived retinal stem cells to study their migration, survival rate, and efficacy is challenged by instability, intracellular aggregation, low uptake, and cytotoxicity. Here, we describe a series of hybrid lipid-coated gold nanorods (AuNRs) that could solve these issues. These nanomaterials were made via a layer-by-layer assembly approach, and their stability in biological media, mechanism, efficiency of uptake, and toxicity were compared with a commercially available set of AuNRs with a 5 nm mesoporous silica (mSiO₂)-polymer coating. These nanomaterials can serve as stem cell labeling and OCT imaging agents because they absorb in the near-infrared (NIR) region away from biological tissues. Although both subtypes of AuNRs were taken up by retinal pigment epithelial, neural progenitor, and baby hamster kidney cells, slightly negatively charged hybrid lipid-coated AuNRs had minimal aggregation in biological media and within the cytoplasm of cells (∼3000 AuNRs/cell) as well as minimal impact on cell health. Hybrid lipid-coated AuNRs modified with cell-penetrating peptides had the least toxicological impact, with >92% cell viability. In contrast, the more "sticky" AuNRs with a 5 nm mSiO₂-polymer coating showed significant aggregation in biological media and within the cytoplasm with lower-than-expected uptake of AuNRs (∼5400 of AuNRs/cell) given their highly positive surface charge (35+ mV). Collectively, we have demonstrated that hybrid lipid-coated AuNRs, which absorb in the NIR-II region away from biological tissues, with tuned surface chemistry can label therapeutic derived stem cells with minimal aggregation and impact on cell health as well as enhance uptake for OCT imaging applications.