In a 2017 paper, a team from Rice University, Durham University, and North Carolina State University reported the development of molecular motors enhanced with small proteins that target specific cancer cells. Once in place and activated with light, the paddlelike motors spin up to 3 million times a second, allowing the molecules to drill through the cells' protective membranes and killing them in minutes.
Since then, researchers have worked on a way to eliminate the use of damaging ultraviolet light. In two-photon absorption, a phenomenon predicted in 1931 and confirmed 30 years later with the advent of lasers, the motors absorb photons in two frequencies and move to a higher energy state, triggering the paddles.
“Multiphoton activation is not only more biocompatible but also allows deeper tissue penetration and eliminates any unwanted side effects that may arise with the previously used UV light,” said Robert Pal of Durham University.
The researchers tested their updated motors on skin, breast, cervical, and prostate cancer cells in the lab. Once the motors found their targets, lasers activated them with a precision of about 200 nanometers. In most cases, the cells were dead within three minutes, they reported. They believe the motors also drill through chromatin and other components of the diseased cells, which could help slow metastasis.
Because the motors target specific cells, James Tour of Rice University said work is underway to adapt them to kill antibiotic-resistant bacteria as well. “We continue to perfect the molecular motors, aiming toward ones that will work with visible light and provide even higher efficacies of kill toward the cellular targets,” he said.