Tiny Traps Capture Individual Blood Cells

Don't worry, they're humane traps—the cells remain alive inside their translucent pyramidal prisons.

Trapped!

An illustration and two microscope images showing the pyramidal self-folding traps and round cells.From Kate Malachowski et al., "Self-Folding Single Cell Grippers," Nano Letters 2014

Gotcha! These little pyramids are actually microscopic traps designed to gently enclose single cells without killing them. The idea is that in the future, such traps could be a part of a system for capturing and analyzing individual cells, perhaps as a part of cancer monitoring.

The traps, which are made out of silicon oxides, start out as flat, star-like shapes. When they're dipped into a saline solution, the arms automatically begin to fold inward along their hinges, capturing any cells that might be nearby at the time. In a new study, the traps' creators have shown the little nano-stars are able to grip two different kinds of mouse cells without killing them: red blood cells and fibroblasts, which are a type of connective tissue cell.

The traps' lead engineer, David Gracias of Johns Hopkins University, has long worked on making microscopic structures that start out flat, but then fold up by themselves. In addition to minute pyramids, he and his lab members have made all kinds of polyhedrons. They've made self-folding structures that fold in response to heat, instead of a dip in saline solution. They've even made microscopic, self-folding shapes with a kind of glue along the edges so they'll seal themselves once they're folded. You can see some of these shapes in a video they published last year. In their latest study, published in the journal Nano Letters, they worked with engineers from the U.S. Army Research Laboratory to make pyramidal grippers that are small enough to capture single cells and have vents so the cells can continue to exchange nutrients and waste with the liquid around them even while they're trapped.

There's a lot of work that the cell-grippers' designers would still need to do to put the grippers into a working product. They might want to be able to target certain cells, for example, instead of just capturing whatever happens by. If these traps are something they want to be able to inject in the human body—and that's what Gracias meant when he talked with Phys.org about using this in vivo—then they'll also have to do a lot of safety testing.