Researchers at Washington University in St Louis have used photo acoustic tomography, a non-invasive imaging technique to understand the transport kinetics of gold nanocages in the lymphatic system. The technique could be used to design new tools for cancer therapy.
Gold nanocages
Gold nanocages were invented by Younan Xia and colleagues at Washington University. These nanostructures have hollow interiors having diameter typically between 30–100 nm and ultra thin porous walls. The structures can be designed to absorb strongly and scatter light in the near-infrared (IR) region of 700–900 nm in the electromagnetic spectrum.
Conventional methods
Tumors spread by invading adjacent issue and cancerous cells propagate throughout the lymphatic system and then into the blood stream. The closest lymph node that drains from a tumor is called the sentinel lymph node (SLN) and this is most likely the area from which metastasis starts. Conventional methods based on injecting organic dyes and hazardous radioactive colloids require surgery. Sentinel lymph node biopsy is an invasive procedure that is used routinely for which SLN mapping is the prerequisite for biopsy. Gold nanoparticles were also earlier used to treat the cancer. Combining the gold nanostructures with specific antibodies or peptides allows them to damage targeted cancerous tissue when illuminated with light at wavelengths around the absorption peak of the gold nanoparticles.
Present technique
The researchers found by injecting a solution of gold nanocages that it traveled through the lymphatic system and accumulated in the lymph nodes of the test animal using reflection-mode photo acoustic imaging technique. The technique relies on pulsing the area of interest with near-IR light from a laser and analyzing the photo acoustic signals generated subsequently by the nanocages therein. The present technique can pinpoint the location of the nanocages accumulated in an SLN at up to 70 nm deep in tissue. The present technique is a non-invasive photo acoustic SLN mapping based on gold nanocages which could be used to greatly aid minimally invasive methods such as fine-needle aspiration biopsy.