Optimising gold nanorod size for maximum photoacoustic response while minimising cell toxicity

Plasmonic nanoparticles show great potential for molecular-targeted photoacoustic (PA) imaging. To maximise light absorption, the gold nanorods (AuNRs) are illuminated at their surface plasmon resonance (SPR), which for biomedical application is typically in the ’optical window’ of 700-900nm. For AuNRs, one of the main factors that determines the SPR is their aspect ratio. Since it is possible to have a similar aspect ratio, but different size of the particle the choice of particle could have a critical effect on a number of factors, such as, photoacoustic emissions, cell toxicity and therapeutic efficacy. For example, a particular sized AuNR may produce a higher PA response, for an equivalent laser fluence, but be more toxic to cell populations. In this study, the PA response of AuNRs with four different volumes but similar aspect ratios (∼4) are compared. A linear relationship between incident laser fluence and PA amplitude is shown and results indicate that AuNRs with larger volumes produce stronger PA emissions. In-vitro cell studies were performed on a lung cancer cell line to assess the cell toxicity of the different sized AuNRs via a colourmetric assay.