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. In this work, we synthesized colloidal porous AuAg alloyed nanoparticles (pAuAg NPs) for enhanced PA imaging.pAuAg NPs were synthesized by galvanic replacement of silver nanocubes. The pAuAg NPs have a 50-nm exteriorsize, and about half of their entire inner space consists of voids that have a bimodal pore distribution with peaksat 21 nm and 8.3 nm. In aqueous in vitro experiments, pAuAg NPs showed 8.9 times higher PA signals than the same number of Au NRs, and 11.7 times higher PA signals than the same number of metal atoms. The PA signal of pAuAg NPs was detected even under 4.5-cm-thick chicken tissue; this result promises a capability for deep-tissue imaging. In whole-body in vivo experiments using a BALB/c mouse, the PA signal of pAuAg NPs showed up to 2.7 times brighter than those of Au NRs under an additional load of 0.8-cm-thick chicken tissue. To further boost the PA signal, silica layers were coated onto pAuAg NPs; these layers increased their PA signals by up to 1.8 times compared to uncoated pAuAg NPs. pAuAg NPs provide strong PA imaging contrast with relatively small dosage. Their inner voids may also permit cargos such as drugs, and their outer surfaces be easily tethered by other functional moieties for applications such as targeting and sensing."