Moving molecules through membranes

Precision analysis with laser light reveals the secrets of transporting drugs across membranes

Getting drugs to the right place can be as important as using the right drugs themselves. A crucial step is often the transport of the drugs through a fatty , such as those surrounding cells. Researchers in China report on their study of key physical and chemical effects controlling drug transport across membranes in the journal .

Packaging drugs inside tiny membrane-bound sacs called  is one option for transporting them around the body, but getting the drugs through membranes to get them into and out of the vesicles as required is challenging. Therefore, whether natural or artificial membranes are involved, crossing a membrane barrier can be vital, and this prompted the researchers to undertake their work.

The team used a sophisticated optical analysis technique called  (SHG) to follow the behaviour of molecules as they encountered and crossed membranes. This involves precise monitoring of how photons of laser light behave in response to the molecules on either side of a membrane.

“Our initial idea was to carry out some studies on anti-cancer drugs and dyes interacting with cancer cells,” explains  of  in Shenzen, China. “This early work revealed that the interactions between drugs and dyes and membranes were very complicated, so we focused on resolving these interaction issues first."

Depending on the chemistry of the solution around them, many drugs can be in electrically charged ionic forms – either positive or negative – or electrically neutral. As an example, the researchers found that the anti-cancer drug  crossed the membrane of a specific type of vesicle in a charged form.

This type of information will be extremely useful for loading vesicles with specific drugs and for understanding the environmental conditions that will allow them to be offloaded at target sites in the body. In the examples studied, varying the ionic composition of a solution – a property known as  – proved key to facilitating transport of the molecules across membranes.

“We are getting a clear understanding of the dynamics and migration forms for the transmembrane delivery of charged molecules and a simple strategy for regulating these dynamic processes,” Gan explains.

In addition to revealing ways to control molecules' movement across membranes, the study also revealed new, and in some cases surprising, details about what happens during the transport process. “We saw a flip-flop movement of some molecules on the lipid surface before crossing the membrane,” says Gan.

Gan adds that a wider implication of the research is demonstrating the power of the SHG technique for studying molecular interactions at interfaces in a non-invasive manner. “We expect more applications for SHG in surface and interface research will be developed,” Gan concludes.

Article details:

Materials Today Physics, Volume 9, June 2019, 100092,

Simple physics in and easy manipulating of the interfacial behavior of charged molecules on drug delivery vesicles

S.-L.Chen, Y.-Z.Liang, Y.Hou, H.Wang, X.Wu, W.Gan, Q.Yuan