Size dependent photoacoustic signal response of gold nanoparticles using a multispectral laser diode system

Photoacoustic imaging is based on the generation of ultrasound using laser irradiation. Recently, gold nanoparticles received a lot of attention due to their excellent suitability for use as contrast agents. For contrast agent analysis, Nd:YAG laser systems are commonly employed, but pulsed laser diodes, which are much smaller and cheaper, can be an attractive alternative. They emit significantly lower pulse energies, but fast averaging is feasible due to high repetition rates. Analysis of contrast agents using laser diodes suffers from vastly different properties of different laser diodes. Here, we present a calibration procedure to correct for some of these differences and enable comparison of results across multiple laser diodes. The calibration procedure is performed for analysis of nanoparticles ranging from diameters of 1 nm to 85 nm. The method is analyzed using two reference materials, Copper Chloride (CuCl₂) and Copper Sulfate (CuSO₄).