Compact Plasmonic Blackbody for Cancer Theranosis in the Near-Infrared II Window.

We have developed a class of blackbody materials, i. e., hyperbranched Au plasmonic blackbodies (AuPBs), of compact sizes (<50 nm). The AuPBs were prepared in a seedless and surfactant-free approach based on the use of mussel-inspired dopamine. Strong intraparticle plasmonic coupling among branches in close proximity leads to intense and uniform broadband absorption across 400-1350 nm. The blackbody absorption imparts the compact AuPB with a superior photothermal efficiency of >80% and closely matched photothermal activity in the first near-infrared (NIR-I) and the second near-infrared (NIR-II) spectral windows, making it a rare broadband theranostic probe for integrated photoacoustic imaging and photothermal therapy (PTT). Our comparative study, using the same probe, has demonstrated that the improved PTT outcome of NIR-II over NIR-I primarily results from its higher maximum permission exposure (MPE) rather than the deeper tissue penetration favored by longer wavelengths. The compact plasmonic broadband nanoabsorbers with tailored surface properties hold potential for a wide spectrum of light-mediated applications.