The use of gold nanorods for photoacoustic molecular imaging with simultaneous multiple targeting is reported. Multiple targeting is done by utilizing the tunable optical absorption property of gold nanorods. This technique allows multiple molecular signatures to be obtained by simply switching laser wavelength. HER2 and EGFR were chosen as the primary target molecules for examining two cancer cells, OECM1 and Cal27. Both in vitro and in vivo mouse model imaging experiments were performed, with contrast enhancement of up to 10 dB and 3.5 dB, respectively. The potential in improving cancer diagnosis is demonstrated.

Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

A metal/phase-change material/metal tri-layer planar chiral metamaterial in the shape of a gammadion is numerically modelled. The chiral metamaterial is integrated with Ge2Sb2Te5 phase-change material (PCM) to accomplish a wide tuning range of the circular dichroism (CD) in the mid-infrared wavelength regime. A photothermal model is used to study the temporal variation of the temperature of the Ge2Sb2Te5 layer and to show the potential for fast switching the phase of Ge2Sb2Te5 under a low incident light intensity of 0.016mW/μm2.

Because of depth-dependent light attenuation, bulky, low-repetition-rate lasers are usually used in most photoacoustic (PA) systems to provide sufficient pulse energies to image at depth within the body. However, integrating these lasers with real-time clinical ultrasound (US) scanners has been problematic because of their size and cost. In this paper, an integrated PA/US (PAUS) imaging system is presented operating at frame rates >30 Hz. By employing a portable, low-cost, low-pulse-energy (~2 mJ/pulse), high-repetition-rate (~1 kHz), 1053-nm laser, and a rotating galvo-mirror system enabling rapid laser beam scanning over the imaging area, the approach is demonstrated for potential applications requiring a few centimeters of penetration. In particular, we demonstrate here real-time (30 Hz frame rate) imaging (by combining multiple single-shot sub-images covering the scan region) of an 18-gauge needle inserted into a piece of chicken breast with subsequent delivery of an absorptive agent at more than 1-cm depth to mimic PAUS guidance of an interventional procedure. A signal-to-noise ratio of more than 35 dB is obtained for the needle in an imaging area 2.8 × 2.8 cm (depth × lateral). Higher frame rate operation is envisioned with an optimized scanning scheme.

Abstract. Photoacoustic tomography ͑PAT͒ has garnered much attention for its high contrast and excellent spatial resolution of perfused tissues. Gold nanorods ͑GNRs͒ have been employed to further enhance the imaging contrast of PAT. However, the photon fluences typically needed for PA wave induction often also result in GNR shape changes that significantly reduce the efficiency of acoustic wave generation. In this work, we propose, synthesize, and evaluate amorphous silica-coated gold nanorods ͑GNR-Si͒ in an effort to improve contrast agent stability and ameliorate efficiency loss during photoacoustic ͑PA͒ wave induction. TEM and optical absorption spectra measurements of GNR and GNR-Si show that encasing GNRs within amorphous silica provides substantial protection of nanorod conformation from thermal deformation. PA signals generated by GNR-Si demonstrate considerably greater resistance to degradation of signal intensity with repetitive pulsing than do uncoated GNRs, thereby enabling much longer, high-contrast imaging sessions than previously possible. The prolongation of high-contrast imaging, and biocompatibility and easy surface functionalization for targeting ligands afforded by amorphous silica, suggest GNR-Si to be potentially significant for the clinical translation of PAT.