The research opens up the possibility of new molecular probes and targeted drug delivery systems

Reviewed by Emily Henderson, B.Sc.November 4, 2020

Researchers at Kanazawa University monitored the blue-green light emission from water-soluble tetraphenylethene molecules adsorbed to a liquid-liquid interface adsorbed by phospholipids, made to resemble a biomembrane. They found that the process could be reversibly controlled by an externally applied potential (voltage), which opens up the possibility for a new class of molecular probes and targeted drug delivery systems.

The targeted delivery of therapeutic drugs or DNA directly to cells has many uses for the treatment of diseases, so there is a growing interest in biomolecules that interact directly with cell membranes. Aggregation-induced emission (AIE), a promising technique with applications for functional materials, optoelectronics, and biomedical engineering, is a process by which autoaggregates can be made fluorescent when stacked together. Tetraphenyletene (TPE) derivatives are helix-shaped molecules with four phenyl rings that exhibit this property. Individually, these molecules are non-fluorescent, because their photoexcited states decay to the ground state by non-emissive molecular vibration or rotation. However, when many of these molecules clump together, they become fluorescent and emit blue-green light.

Researchers from the Kanazawa University Institute of Science and Engineering studied the AIE behavior of water-soluble TPE derivatives on an artificial cell membrane surface formed by the self-assembly of phospholipid molecules, each of which has a hydrophilic head (which loves water) “” and two hydrophobic “tails” (fearful of water). Phospholipids can also be used to create bubbles called vesicles that can fuse with living cell membranes to deliver a drug or DNA payload.

Potential applications of this work include selective labeling of targeted drug-containing vesicles. “

Hirohisa Nagatani, senior author of the study

Using ion transfer voltammetry and surface-sensitive modulation spectroscopy, the research team was able to demonstrate that phase transfer and interfacial adsorption of charged TPE molecules occurred reversibly based on a applied potential. This mimics the membrane potential of living cells, which plays a crucial role in many physiological processes, including ion transport and the transmission of nerve impulses.

“The voltage-induced behavior we observed in simple water-soluble molecules may be important for the development of novel membrane potential sensitive probes for biomedical applications,” Nagatani explains. “Our system could also be an alternative to voltage-sensitive dyes such as molecular probes.” The researchers also note the possibility of using this system as a photosensitizer for cancer phototherapy, in which cells can be selectively tagged for light radiation.