A scanning-electron microscope image of chemically-fixed HeLa cancer cells on the substrate. (Credit: Harvard University)
The ability to deliver cargo like drugs or DNA into cells is essential for biological research and disease therapy but cell membranes are very good at defending their territory.
Researchers have developed various methods to trick or force open the cell membrane but these methods are limited in the type of cargo they can deliver and aren’t particularly efficient.
Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new method using gold microstructures to deliver a variety of molecules into cells with high efficiency and no lasting damage. The research is published in ACS Nano.
“Being able to effectively deliver large and diverse cargos directly into cells will transform biomedical research,” says Nabiha Saklayen, a PhD candidate in the Mazur Lab at SEAS and first author of the paper.
“However, no current single delivery system can do all the things you need to do at once. Intracellular delivery systems need to be highly efficient, scalable, and cost effective while at the same time able to carry diverse cargo and deliver it to specific cells on a surface without damage. It’s a really big challenge.”
In previous research, Saklayen and her collaborators demonstrated that gold, pyramid-shaped microstructures are very good at focusing laser energy into electromagnetic hotspots. In this research, the team used a fabrication method called template stripping to make surfaces—about the size of a quarter—with 10 million of these tiny pyramids.
“The beautiful thing about this fabrication process is how simple it is,” says Marinna Madrid, coauthor of the paper and PhD candidate in the Mazur Lab. “Template-stripping allows you to reuse silicon templates indefinitely. It takes less than a minute to make each substrate, and each substrate comes out perfectly uniform. That doesn’t happen very often in nanofabrication.”
The team cultured HeLa cancer cells directly on top of the pyramids and surrounded the cells with a solution containing molecular cargo.
Using nanosecond laser pulses, the team heated the pyramids until the hotspots at the tips reached a temperature of about 300 degrees Celsius. This very localized heating—which did not affect the cells—caused bubbles to form right at the tip of each pyramid. These bubbles gently pushed their way into the cell membrane, opening brief pores in the cell and allowing the surrounding molecules to diffuse into the cell.
