Stabilizing Gold Nanotetrapods via in Situ Polymerization for Superior Photoacoustic and Photothermal Applications

Gold nanotetrapods (NTPs) possess sharp branched tips, high surface-to-volume ratios, and strong localized surface plasmon resonance in the near-infrared (NIR) region, making them candidates for biomedical applications. However, their practical use is limited by structural instability and inadequate biocompatibility in complex physiological environments. In this study, we developed an innovative in situ radical polymerization technique to encapsulate NTPs with a thin, cross-linked zwitterionic polymer shell, forming highly stable and biocompatible nanoparticles (NTP@XP). The polymer shell preserved the tetrapod structure and endowed NTPs with tunable surface properties through the polymerization of different monomers. Under NIR irradiation, NTP@XP exhibited enhanced photoacoustic imaging and a photothermal conversion performance in vitro. In vivo, the antifouling and biocompatible coating of NTP@XP allowed durable imaging and suppressed tumor regrowth in mice. This work establishes in situ polymerization as a robust strategy to stabilize NTPs, paving the way for various biomedical fields.