Hyperbolic metamaterial nanoparticles random array for thermoplasmonics in the II and III near-infrared windows

Plasmonic nanostructures capable of converting light to heat have found wide applications, thus giving rise to the field of thermoplasmonics. Among them, the use of gold-based plasmonic structures in near-infrared (NIR) spectral regions has catalyzed substantial research efforts due to the potential impact in clinical therapy applications. However, the photon scattering effect scaling with the square of the nanoparticle volume leads to high scattering and then low absorption efficiency. This limit has hindered the exploitation of gold nanoparticles, especially in NIR II regions above 1000 nm. Here, we make a step forward for overcoming this limitation by introducing hyperbolic metamaterial nanoparticles that are made of multi-layered gold/dielectric nanodisks and exhibit >70% absorption efficiency in the NIR II and III regions. Their high light-to-heat conversion is demonstrated by a much larger temperature increase than that of gold nanodisks with the same amount of gold. Efficient in vitro hyperthermia of living cells with negligible cytotoxicity shows the potential of our platform for versatile bio-medical applications.