Noninvasive photoacoustic sentinel lymph node mapping using Au nanocages as a lymph node tracer in a rat model

Sentinel lymph node biopsy (SLNB) has been widely performed and become the standard procedure for axillary staging in breast cancer patients. In current SLNB, identification of SLNs is prerequisite, and blue dye and/or radioactive colloids are clinically used for mapping. However, these methods are still intraoperative, and especially radioactive colloids based method is ionizing. As a result, SLNB is generally associated with ill side effects. In this study, we have proposed near-infrared Au nanocages as a new tracer for noninvasive and nonionizing photoacoustic (PA) SLN mapping in a rat model as a step toward clinical applications. Au nanocages have great features: biocompatibility, easy surface modification for biomarker, a tunable surface plasmon resonance (SPR) which allows for peak absorption to be optimized for the laser being used, and capsule-type drug delivery. Au nanocage-enhanced photoacoustic imaging has the potential to be adjunctive to current invasive SLNB for preoperative axillary staging in breast cancer patients.