Selenium‐Integrated Cyanine Dye With Enhanced Photophysical Properties for Optoacoustic‐Guided Cancer Imaging and Therapy

ABSTRACT Near‐infrared (NIR) cyanine dyes demonstrate considerable promise in medical applications, notably in cancer diagnosis, due to their favourable fluorescence properties and biocompatibility. However, these dyes generally have low photostability and tend to aggregate in aqueous solution, which can constrain their usefulness for prolonged in vivo imaging and phototherapy applications. Here, we report the synthesis of a selenium‐integrated NIR cyanine dye, Se‐Cyn, designed to modulate its electronic and photophysical properties. Se‐Cyn demonstrates high photostability, molar absorptivity, photothermal conversion efficiency (PCE), and sustained optoacoustic (OptA) contrast under prolonged irradiation. Se‐Cyn nanoparticles (NPs) outperform the indocyanine green (ICG) NPs, exhibiting PCE of 59% and a 1.36‐fold higher OptA generation efficiency. Additionally, nano‐formulated Se‐Cyn NPs show excellent aqueous stability and improved bioavailability, supporting its suitability for biological applications. Furthermore, Se‐Cyn NPs accumulate in tumors following systemic administration, enabling effective OptA tumor imaging. Together with their strong photodynamic and photothermal properties, these NPs show considerable potential for cancer theranostics.