Making light work of synthetic membrane pores

Researchers at King Abdullah University of Science and Technology (KAUST), Saudi Arabia, took inspiration from light-controlled channels in cell membranes to develop a synthetic equivalent. They anticipate possible applications in nanotechnology and nanomedicine.

In living cells, changes in light levels can stimulate the opening and closing of protein channels in cell membranes to control the movement of charged particles called ions into and out of a cell. 

These natural ‘light-gated ion channels’ are attracting attention from scientists interested in their potential to control the flow of ions and molecules in nanotechnology applications. However, using the natural channels is difficult because these protein-based systems are unstable when removed from their normal environment.

The KAUST team confronted this problem by designing their own synthetic light-gated channels from the bottom up. They worked with materials called conjugated microporous polymers (CMPs), whose chemical structure creates uniformly sized pores when they are formed into a membrane. The trick achieved by the KAUST team was to make pores that change significantly in size in response to light. They designed and fabricated a CMP in which light induces a significant chemical structural change called isomerization. This allows different wavelengths of light to reversibly widen or narrow the pores. 

“The changes in pore size and porosity of the smart membrane are difficult to determine,” says chemical engineer, Zhiping Lai, who led the research group. “We had to make hundreds of samples to overcome this issue.”

By exploring the effects of different chemical structures, Lai and his colleagues eventually demonstrated the light-induced transport of different types of ions across their membranes. 

“The concept of light-gated smart CMPs can be extended beyond membrane applications,” Lai adds. This suggests that, in principle, the materials could be useful for applications like nanoscale computational memory systems, photo-responsive chemical sensors, light-controlled electronics including supercapacitors, or smart drug release vehicles that would deliver their cargo only where and when induced to do so by the application of light.

Lai says that the next plan for his group is to try to use their membranes to make useful light-sensitive sensors.

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