Developing gold nanotubes as photoacoustic contrast agents

Photoacoustic imaging (PAI) combines the spectral selectivity of laser excitation with the high resolution of ultrasound imaging, representing a noninvasive modality that holds remarkable potential for clinical translation. In particular, multispectral optoacoustic tomography has emerged has an innovative PAI technology, which enables high detection specificity by resolving multiple spectral signatures through tissues and accurately decomposing the biodistribution of relevant molecules from non-specific background contributions. Key criteria for developing PAI contrast agents include strong absorbance in the near-infrared (NIR) tissue transparent region and low toxicity. In this study, we have fabricated gold nanotubes (Au NTs) with controlled length and NIR absorption for the application as in vivo MSOT contrast agents. The length control relies on the synthesis of silver nanorod template under certain growth conditions. The Au NTs were coated with a layer of biocompatible polymer, poly(sodium 4-styrenesulfonate) (PSS), to ensure colloidal stability and low cytotoxicity. The PSS-Au NTs have shown excellent MSOT signal enhancement on tissue-mimicking phantom and in vivo, demonstrating the potential for further development towards a theranostic nanoplatform integrating PAI capability and therapeutic functions.