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.

Functional Photoacoustic Imaging for Placental Monitoring: A Mini Review.

The placenta, a highly vascularized interface between the mother and fetus, undergoes dramatic anatomical and functional changes during pregnancy. These changes occur both during healthy development and adverse pathologies of pregnancy, such as preeclampsia (PE). Abnormal placental development can lead to life-long health impacts on both the mother and child. Photoacoustic (PA) imaging, extensively developed for preclinical imaging applications in oncology and cardiovascular disease, uses optical energy to generate acoustic waves through thermoelastic expansion of light-absorbing chromophores within tissue. Recently, PA imaging has been used to study preclinical placental anatomy and function. If clinical translation of PA imaging of the placenta is achieved, the impact on maternal-fetal health could be expansive. This perspective highlights the recent progress in PA imaging for placental monitoring and discusses the progress needed for human clinical translation.

Accuracy of retrieving optical properties from liquid tissue phantoms using a single integrating sphere.

Using integrating spheres (ISs) in conjunction with the inverse adding-doubling algorithm (IAD) offers a well-established, rigorous protocol for determining optical absorption (µa) and reduced scattering (µs') coefficients of thin, optically homogeneous, turbid media. Here, we report the performance and use of a single IS system for experimentally retrieving optical properties in phantom media whose optical properties were well controlled. The IS system was used to measure the total reflectance and transmittance between 500 and 800 nm in liquid phantoms that were prepared to span a wide range of optical scattering and absorption coefficients. Measurements on phantoms were sequentially made using one of two broadband light sources-a halogen lamp or a supercontinuum laser. We report on the accuracy of IAD-derived optical coefficients using IS measurements made on phantoms-directly or by employing one of two previously reported correction methods. The first (sample-substitution error) correction was experimentally achieved while the second used Monte Carlo-based corrections with IAD. When experimentally calibrated reflectance and transmittance values were directly used as inputs to the IAD, mean absolute errors in recovered optical coefficients were larger than 0.4cm-1 for absorption and more than 6cm-1 for scattering across all phantoms and wavelengths measured. These errors reduced to 0.06-0.17cm-1 and 0.7-2cm-1 for µa and µs', respectively, with the use of corrections. Choice of light sources used, sample geometry (relative to optical coefficients), signal-to-noise of measurements, and the selection of correction methods are discussed.