Enhancing the photothermal stability and photothermal efficacy of AuNRs and AuNTs by grafting with Ru(ii) complexes

Abstract

Gold nanorods (AuNRs) and nanostars (AuNTs) were widely applied in photothermal cancer therapy recently. However, due to the photothermal effect, naked AuNRs and AuNTs easily melt into gold spheres. This drawback results in loss of the characteristic near-infrared (NIR) surface plasmon resonance (SPR) and limits their therapeutic applications. In this paper, we reported that ruthenium(II) complex-functionalized AuNRs (AuNRs@Ru) and AuNTs (AuNTs@Ru) exhibit higher photothermal stability and photothermal efficiency than naked AuNRs and AuNTs. AuNRs@Ru and AuNTs@Ru maintain the morphology and NIR SPR absorption of gold nanoparticles upon 0.25 W cm⁻² laser irradiation, which is lower than the maximal permissible exposure of skin as per ANSI regulation (0.33 W cm⁻² at 808 nm). Further photothermal therapy studies on three-dimensional (3D) HeLa spheroids and an in vivo tumor model show that AuNRs@Ru and AuNTs@Ru are more effective for the photothermal destruction of tumors than AuNRs and AuNTs.