In this paper, lipophilically modified silica coated gold nanorods were developed to enhance the photoacoustic response of contrast agents. Photoacoustic imaging become a popular technique in the diagnostic imaging because it can utilize light at larger penetration depths and better resolution than optical coherence tomography or fluorescence imaging. In addition, photoacoustic imaging can augment optical microscopy to image in high scattering tissue. To boost signal, many exogenous contrast agents have been synthesized. However, these agents are still limited to a linear dependence of signal on laser fluence, which limits the benefits for imaging in scattering media. The ability of agents to induce cavitation events in response to laser irradiation would both increase signal and promote nonlinearity. In this work, silica coated gold nanorods with a longitudinal plasmon peak of 750-800 nm were lipophilically modified to facilitate the formation of cavitation nuclei on the rod’s surface. It was found that the lipophilically modified silica coated gold nanorods were able to achieve nonlinearity at pulse radiant exposures greater than 8 mJ/cm<sup>2</sup>. At radiant exposures of 21 mJ/cm<sup>2</sup>, the photoacoustic response was 13-15 times higher than unfunctionalized gold nanorods. The concentration of the samples was also investigated, and it was found that the photoacoustic response was greater for samples with higher concentrations than ones that were lower.  Finally, the lipohilically modified silica coated gold nanorods were more resistant to etching in aqueous media, showing stability for more than one month in PBS.

Exploring the role of hydrophobic modification for generating enhanced photoacoustic responses from silica coated gold nanorods

ACS Spring Meeting 2021

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