Monodisperse Sub-100 nm Au Nanoshells for Low-Fluence Deep-Tissue Photoacoustic Imaging.

Nanoparticles with high absorption cross sections will advance therapeutic and bioimaging nanomedicine technologies. While Au nanoshells have shown great promise in nanomedicine, state-of-the-art synthesis methods result in scattering-dominant particles, mitigating their efficacy in absorption-based techniques that leverage the photothermal effect, such as photoacoustic (PA) imaging. We introduce a highly reproducible synthesis route to monodisperse sub-100 nm Au nanoshells with an absorption-dominant optical response. Au nanoshells with 48 nm SiO2 cores and 7 nm Au shells show a 14-fold increase in their volumetric absorption coefficient compared to commercial Au nanoshells with dimensions commonly used in nanomedicine. PA imaging with Au nanoshell contrast agents showed a 50% improvement in imaging depth for sub-100 nm Au nanoshells compared with the smallest commercially available nanoshells in a turbid phantom. Furthermore, the high PA signal at low fluences, enabled by sub-100 nm nanoshells, will aid the deployment of low-cost, low-fluence light-emitting diodes for PA imaging.

Emergent properties from CuPd alloy films under near-infrared excitation.

Noble-transition metal alloys offer emergent optical and electronic properties for near-infrared (NIR) optoelectronic devices. We investigate the optical and electronic properties of CuxPd1-x alloy thin films and their ultrafast electron dynamics under NIR excitation. Ultraviolet photoelectron spectroscopy measurements supported by density functional theory calculations show strong d-band hybridization between the Cu 3d and Pd 4d bands. These hybridization effects result in emergent optical properties, most apparent in the dilute Pd case. Time-resolved terahertz spectroscopy with NIR (e.g., 1550 nm) excitation displays composition-tunable electron dynamics. We posit that the negative peak in the normalized increment of transmissivity (ΔT/T) below 2 ps from dilute Pd alloys is due to non-thermalized hot-carrier generation. On the other hand, Pd-rich alloys exhibit an increase in ΔT/T due to thermalization effects upon ultrafast NIR photoexcitation. CuxPd1-x alloys in the dilute Pd regime may be a promising material for future ultrafast NIR optoelectronic devices.