The Effect of Different Stabilisers on Stability and Photothermal Profiling of Gold Nanorods

The photothermal application of gold nanorods (AuNRs) as a photothermal agent has gained popularity due to their optical, photothermal and biological properties. However, AuNRs are synthesised using a biotoxic surfactant (cetyl trimethyl ammonium bromide) which limits their biological applications. Though different techniques have been established to address this challenge using different stabilizers or passivating agents, the effect of these stabilizers on AuNRs' colloidal stability, thermal stability, and photothermal conversion efficiency still need to be investigated. In this study, we evaluated the effect of different polymers or stabilisers; two synthetic polymers [methoxy polyethylene glycol thiol (mPEG-SH) and polyvinylpyrrolidone (PVP)] and one biopolymer (gelatin) on the stability and photothermal properties of AuNRs. AuNRs absorbing around 800 nm were synthesised and coated with these three stabilisers. The colloidal stability of the as-synthesised material was evaluated in Dulbecco's phosphate-buffered saline (PBS) and Roswell Park Memorial Institute (RPMI-1640) using Ultraviolet–Visible–Near-Infrared (UV–Vis–NIR). The results show that PEG@AuNRs was more stable in both media due to fewer functional groups on its structure to bond with ions and protein. PVP@AuNRs showed good thermal stability under heat incubation (at 37, 50 and 70 °C) for 24 h because of its high thermal decomposition properties, while PEG@AuNRs proved superior in improving the AuNRs heat generation. In addition, coating with different polymers did not affect the photothermal ability of AuNRs. This study demonstrated that it is crucial to choose polymers with less functional groups when coating nanoparticles for biological application.