Photothermal Therapy - Recent Study

Recent Study

One of the biggest recent successes in photothermal therapy is the use of gold nanoparticles. Spherical gold nanoparticles absorptions have not been optimal for in-vivo applications. This is because the peak absorptions have been limited to 520 nm for 10 nm diameter silicon nanoparticles to only 580 nm for gold nanoparticles approximately 100 nm in diameter. Skin, tissues, and hemoglobin have a transmission window from 650 nm up to 900 nm with a peak transmission at approximately 800 nm known as the Near-Infrared Window. This was solved with the recent invention by Cathy Murphy of gold nanorods. The peak absorption of gold nanorods may be tuned from 550 nm up to 1 micrometre by altering its aspect ratio. Once tuned, scientists have learned how to remove the toxic byproduct of CTAB with non-cytotoxic polyethylene glycol (PEG). The PEG not only keeps the nanorods from aggregating in serum once injected, they also lend to long circulation times for the gold nanorods. Research has shown that the longer the circulation time, the better adsorption of the nanorods into the cancer tumor. This is non-directional (enhanced permeability and retention effect) and has shown better than 7% accumulation in the cancer tumor from an intravenous injection. Current studies have shown half life circulation times of greater than 15 hours. Once the nanorods have cleared the blood stream, the cancer tumor may be illuminated ex vivo with a diode laser. Nanorods located at distances 10 times their size can still absorb 80% of the incident light energy creating massive heat load to the surrounding cancer tumor. Current studies involve mice but are being extended.