Evaluation of nanoparticles as contrast agent for photoacoustic imaging in living cells

Photoacoustic imaging is a hybrid imaging modality combining beneficial features from optical and ultrasound techniques. In photoacoustic imaging, the thermoelastic effect is used for laser-induced generation of ultrasound waves. Absorption of light in tissue leads to small increase in temperature which results in volume expansion and generation of pressure waves. For contrast enhanced imaging, different types of contrast agents can be used. Depending on the geometrical shape plasmon resonance material shows high absorbing properties in the near infrared (NIR). The absorption maximum of existing nanoparticulate contrast agents is located in the range between 700 nm and 900 nm. Due to the limited number of technically available lasers emitting in this spectral range as well as the controversial discussed questions about cytotoxicity, the widespread clinical use is limited. In order to allow a future use of photoacoustic imaging in the clinical routine, laser systems comb ining the availability of a near-infrared (NIR) wavelength with cost-efficiency and easy-handling such as Nd:YAG lasers (1064nm laser beam) combined with a bioconjugated contrast agent have to be used for signal generation. The aim of this study was to synthesize gold nanoparticles and infrared dye (IR5)-loaded PLGA (poly(D,L-lactide-co-glycolide)) particles with an absorbance maximum in the range of 1100 nm, to be compatible with the laser system, and to characterize their cytotoxicity with regard to the application as contrast agents for photoacoustic imaging. Using human liver carcinoma cells (HepG2) in vitro experiments were performed after four different exposure times to guarantee the biocompatibility of the synthesized nanoparticles. The results indicate that both nanoparticulate systems induce no cytotoxic effects. Using the developed highly sensitive high-resolution photoacoustic microscope platform based on the SASAM acoustic microscopy system concentration-dependent in vitro detection of