Porous Gold-Silver Alloy Nanoparticles for Photoacoustic Signal Enhancement

Abstract

Photoacoustic(PA) imaging is an emerging tool that can solve the traditional problems of optical imaging such as imaging depth and resolution. Using the acoustic waves generated in response to the absorption of pulsed laser light, PA imaging can provide non-invasive images of live species. In addition, PA imaging shows several centimeters of penetration depth and a few hundred micrometers of resolution, due to lower scattering of acoustic waves in tissue than photons. Because of these advantages, PA imaging shows great potentials for clinical research and application. Au nanostructures are suitable contrast agents because of their high extinction coefficient, thermal conversion efficiency and biocompatibility. In this work, we synthesized porous AuAg alloy nanoparticles(NPs) for PA contrast agent with large surface area, which is advantageous in terms of thermal conduction and heat conversion. Porous AuAg alloy NPs were synthesized by galvanic replacement reaction from silver nanocubes. All synthetic procedures were observed by TEM images and absorption spectra. Acoustic signal increase was confirmed in the 680-800 nm NIR region compared to gold nanorods with the similar absorption cross-section in solution, for phantom gel and small animal level. Especially, 24 times increase of PA signal was observed in solution. This result shows that surface area of contrast agents is important for thermal conversion efficiency for PA signal. Our porous AuAg alloy NPs can be a platform for many applications, in addition to the PA imaging contrast, such as drug delivery vehicle, which suits well for future theranostic applications.