Optimization of the synthesis conditions of gold nanoparticle–polydimethylsiloxane composites for ultrasound generation

Abstract

Gold nanoparticle (AuNP)–polydimethylsiloxane (PDMS) composites are promising materials for photoacoustic (PA) generation owing to their high thermal dilatation coefficient, small thermal capacity and acoustic impedance close to that of water. Solvent choice during AuNP synthesis can dramatically enhance the optical absorption of the composite, but there is no unified picture on this parameter. Here we test the optical absorbance and photoacoustic amplitude of AuNP–PDMS composites synthesized in five common solvents (acetone, methanol, ethanol, isopropanol, and water). We find that photoacoustic signals from water and acetone yield small and sharp acoustic displacement peaks whereas those from alcohols yield larger step-like downward displacements (away from the conversion layer), which indicates a different Grüneisen parameter between the two groups. Furthermore, our experiments show that composites synthesized in isopropanol instead of ethanol showed a homogeneous surface and a nearly total optical absorption on a narrow bandwidth, and boosted the photoacoustic amplitude by up to 20%.