Delivering a drug to specific cell or tumor has been an ongoing challenge in the field of oncologic therapeutics and immunotherapy. As a measure of such progress, the utility of PD-1 and check point inhibitors (CTLA-4) for treatment of melanoma and non small cell lung cancer has been encouraging.

Operating at the nano level may more accurately represent the holy grail for targeted delivery of drugs , but has been hampered by technological issues involving fine control and release of therapeutics, similar to the engagement of a molecular switch. Achieving this fine control has been one of the principal ongoing challenges.

Just as electrical transistors have been the workhorses within microchips contained inside our electronic devices, recent advances in nanotechnology to activate cellular functions by molecular switching are becoming a reality by virtue of a new approach taking advantage of the basic principles of photons contained in visible light.

Researchers at the University of Texas at Austin have now identified the first approach for altering the mechanical motion of nanomotors by using visible light as the stimulus.

Donglei (Emma) Fan, Associate Professor at the Cockrell School of Engineering's Department of Mechanical Engineering, and Ph.D. candidate Zexi Liang, made the discovery of how the variation in light intensity can increase, stop and reverse the rotational orientation of silicon nanomotors in an electric field. It’s akin to producing a switch which alters the mechanical motion of rotary nanomotors which changes their direction instantly, similar to an “on-off” switch.

Their research was recently published in Science Advances.

In simple terms, nanomotors are the way nanoscale devices transform energy into movement at both the molecular and cellular level.

The implications of this discovery are far reaching and have the ability to lead to a new class of devices --nanoelectromechanical and nanorobotic--with the potential to impact the field of drug delivery, wireless communication, optical sensing, as well as molecule release and detection.

The researchers utilized light from a laser at variable strengths and intensity--from visible to infrared--to alter the motion of nanomotors.

While research has already been done evaluating the feasibility of using nanomotors with variable speed control as a method of drug delivery, UT researchers took this a step forward, using light to adjust the mechanical motion itself--a discovery that has much greater implication for the integration and ability to alter nanomotors in electronic devices.

"The ability to alter the behavior of nanodevices, from passive to active opens the door to the design of autonomous and intelligent machines at the nanoscale," Fan said in a press release.

"We were able to distinguish semiconductor and metal nanomaterials just by observing their different mechanical motions in response to light with a conventional optical microscope. This distinction was made in a noncontact and nondestructive manner compared to the prevailing destructive contact-based electric measurements."

The discovery of light acting as a switch for adjusting the mechanical behaviors of nanomotors was based on examinations of the interactions of light in the setting of an electric field and semiconductor nanoparticles converging in a water-based solution.

This is actually Fan’s second breakthrough discovery in this arena. In 2014, she and her team developed the smallest, fastest and longest-running rotary nanomotors. These nanomotors, less than 1 micrometer in dimension, are capable of being placed inside a human cell with the ability to rotate nonstop for 15 hours at 18,000 RPMs—the speed of the motor in a jet engine. Similar nanomotors that have been developed operate at much slower speeds (14 RPMs to 500 RPMs), rotating from a few seconds to a few minutes.

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