Silica-coated gold nanoplates as stable photoacoustic contrast agents for sentinel lymph node imaging

A biopsy of the first lymph node to which a tumor drains—the sentinel lymph node (SLN)—is commonly performed to identify micrometastases. Image guidance of the SLN biopsy procedure has the potential to improve its accuracy and decrease its morbidity. We have developed a new stable contrast agent for photoacoustic image-guided SLN biopsy: silica-coated gold nanoplates (Si-AuNPs). The Si-AuNPs exhibit high photothermal stability when exposed to pulsed and continuous wave laser irradiation. This makes them well suited for in vivo photoacoustic imaging. Furthermore, Si-AuNPs are shown to have low cytotoxicity. We tested the Si-AuNPs for SLN mapping in a mouse model where they exhibited a strong, sustained photoacoustic signal. Real-time ultrasound and photoacoustic imaging revealed that the Si-AuNPs quickly drain to the SLN, gradually spreading throughout a large portion of the node. (paper)