Local anesthesia is often preferable to general anesthesia for medical procedures due to reduced side effects. However, its effects have a fixed duration and cannot be switched on or off as needed.

Daniel S. Kohane, Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA, and colleagues have developed temperature-sensitive liposomes (spheres with a lipid bilayer boundary). The liposomes contain tetrodotoxin (TTX) and dexmedetomidine (DMED), a potent mixture of local anesthetics. The team functionalized the surface of the liposomes with biotin and added streptavidin-functionalized gold nanorods. Streptavidin interacts strongly with biotin and thus binds the gold nanorods to the liposomes. The nanorods heat up under near-infrared (NIR) light, which disrupts the lipid bilayer and releases the active compounds.

The researchers tested the formulation by injecting rats with the liposomes. After the initial anesthetic effect wore off, they irradiated the injection location with NIR light. They found that the NIR light could be used to switch on the anesthetic effect several more times. According to the team, the approach could, e.g., be useful to treat pain after operations with on-demand irradiation. This could reduce the need for addictive opioids.

• Ultrasensitive Phototriggered Local Anesthesia,
  Changyou Zhan, Weiping Wang, Claudia Santamaria, Bruce Wang, Alina Rwei, Brian P. Timko, Daniel S. Kohane,
  Nano Lett. 2017.
  DOI: 10.1021/acs.nanolett.6b03588