Photoacoustic Imaging of Mesenchymal Stem Cells in Living Mice <i>via</i> Silica-Coated Gold Nanorods

TLDR

Improved imaging modalities are critically needed for optimizing stem cell therapy, especially real‑time techniques that guide and quantify cell implantation in musculoskeletal regenerative medicine. The study reports using silica‑coated gold nanorods as a contrast agent for photoacoustic imaging and quantitation of mesenchymal stem cells in rodent muscle tissue. Silica‑coated gold nanorods were employed as a photoacoustic contrast agent to image and quantify mesenchymal stem cells in rodent muscle. The silica coating boosted gold uptake five‑fold without affecting cell viability or pluripotency, allowed photoacoustic imaging of as few as 100 000 cells with 340 µm spatial and 0.2 s temporal resolution, and outperformed PET and MRI by enabling real‑time monitoring of stem cell therapy.

Abstract

Improved imaging modalities are critically needed for optimizing stem cell therapy. Techniques with real-time content to guide and quantitate cell implantation are especially important in applications such as musculoskeletal regenerative medicine. Here, we report the use of silica-coated gold nanorods as a contrast agent for photoacoustic imaging and quantitation of mesenchymal stem cells in rodent muscle tissue. The silica coating increased the uptake of gold into the cell more than 5-fold, yet no toxicity or proliferation changes were observed in cells loaded with this contrast agent. Pluripotency of the cells was retained, and secretome analysis indicated that only IL-6 was disregulated more than 2-fold from a pool of 26 cytokines. The low background of the technique allowed imaging of down to 100 000 cells in vivo. The spatial resolution is 340 μm, and the temporal resolution is 0.2 s, which is at least an order of magnitude below existing cell imaging approaches. This approach has significant advantages over traditional cell imaging techniques like positron emission tomography and magnetic resonance imaging including real time monitoring of stem cell therapy.