Gold-silica plasmonic nanobones with tunable size and optical bimodality for bioimaging

Silica-coated gold nanotags were developed for multimodal Raman and fluorescent imaging. These nanotags, shaped like bones, offer significant absorption at 700 nm, aligning with the first window of tissue transparency. Gold nanobones were modified with cyanine 5.5 and 7 dyes and a silica shell for stability and biocompatibility via a modified Stober method involving tetraethoxysilane hydrolysis. Folic acid was attached on outer surface of nanotags to serve as a model delivery vector. The nanotags were characterized by dynamic light scattering, transmission electron microscopy, and spectroscopy. These methods showed that a thickness of the silica shell can be precisely controlled via a concentration of tetraethoxysilane. Surface-enhanced Raman scattering and emission spectra were registered and demonstrated the intensity dependent on the distance between the dye and core. Raman mapping of cell samples highlighted the nanotags bioimaging potential and revealed the partial nanotags agglomeration post-cell uptake accompanied by formation of optical hot-spots. Cell viability assays with HeLa and HEP 2 G cell lines suggested the nanotags safety below 0.2 mg/L concentration. These findings highlight the benefits of silica-coated gold nanotags and open the doors in advanced medical imaging.