PEGylated gold nanorods with a broad absorption band in the first near-infrared window for in vivo multifunctional photoacoustic imaging

Nanoparticles with absorbances in the near-infrared window (NIR, 700–1300 nm) are ideal contrast agents for in vivo imaging of deep tissue with high signal-to-noise ratios. By using CTAB and l(+)-ascorbic acid (AA) as ligands to effectively balance particle nucleation and growth, PEGylated Au nanorods (NRs) with broad absorption bands (from 650 to 1100 nm) in the first NIR window could be successfully realized. The morphologies, crystal structures, absorption and biotoxicities of the samples were determined by TEM, TGA, UV-vis and MTT assay. The results indicated that the presence of a thin poly(ethylene glycol) (PEG) shell could greatly improve the biocompatibility of the Au NRs (1.7 times that of non-PEGylated Au NRs), making them harmless to living cells. Moreover, the prepared PEGylated Au NRs displayed the highest image contrast and SNR values (1.1–1.5 times that of commercial Au nanospheres and NRs), with excitation lasers of 532, 680 and 828 nm, showing their great potential for use in multicolor photoacoustic imaging in vivo. With the prepared PEGylated Au NRs, a functional image of oxygen saturation was constructed in a single step without changing the contrast agent.