Gold nanostar-enhanced multimodal photoacoustic microscopy and optical coherence tomography for the visualization of laser-induced choroidal neovascularization in living rabbits

Photoacoustic microscopy (PAM) is a novel and hybrid optical and acoustic technique for imaging. This modality can be used for label-free imaging of the retinal microvasculature with ultrahigh resolution and excellent image contrast. However, it is hard to distinguish newly developed microvasculature from native vessels. An exogenous photoabsorber contrast agent can boost the sensitivity and enhance the PAM image contrast. The focus of this study is to investigate the potential application of gold nanostars (GNS) as a contrast agent for multimodal PAM and OCT. GNS were validated on Rose Bengal laser-induced retinal vein occlusion choroidal neovascularization (CNV) rabbit model. Four New Zealand white rabbits were administrated with Rose Bengal (5 mg/kg) followed by laser illumination at a power of 300 mW. CNV developed at day 28 post laser illumination. The rabbit model before and after treatment was monitored by a multimodal imaging system including OCT, PAM, color fundus photographs, fluorescein angiography, (FA) and indocyanine green angiography (ICGA). At day 28 post laser treatment, the rabbits received an intravenous injection of 400 μL GNS at a concentration of 2.5 mg/mL. Multimodal PAM and OCT monitored the GNS at various time points: 1 h, 2 h, 8 h, 24 h, 48 h, 72 h, day 4, day 7, day 9, day 11 and day 14. The experimental results show that the PA signal was enhanced 24-fold and OCT intensity increased 184% 24 h post injection. Histological analysis and TUNEL assay show no evidence of any change in cell nuclear morphology suggesting no damage or cell death. In addition, the liver function tests showed normal liver and kidney function, indicating that GNS induced no toxicity in the rabbit at the treated concentration. Therefore, GNS may provide a safe and potential contrast agent for the detection of the microvasculature in the eye.