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How spongy silicon could open new doors in bioelectronics

New form of silicon boosts element’s biocompatibility and activates neurons with an assist from light

by Matt Davenport
June 27, 2016

Credit: Nat. Mater.
Deformable silicon particles are made from a network of wires less than 10 nm in diameter connected by nanoscopic bridges, as shown in this schematic.

Silicon is the best semiconductor on the periodic table for researchers trying to connect smart devices to living cells, says Bozhi Tian of the University of Chicago. Silicon is biocompatible and biodegradable, and scientists have already developed electronic implants and biosensors using silicon. But conventional single-crystalline silicon is inherently rigid, which can prove irritating to living tissue.

Along with Francisco Bezanilla, Tian and his colleagues have now developed spongy silicon particles that are deformable and, therefore, are less likely to inflame their surroundings (Nat. Mater. 2016, DOI: 10.1038/nmat4673). Another key benefit is that amorphous silicon absorbs light better than single crystals, allowing the team to create efficient links to living cells, Tian explains.

The team demonstrated this by attaching single, micrometer-sized particles of its spongy material to rat neurons grown in a dish. When illuminated with green laser light, the particles cause electrical current to flow into the nerve cells. This, in turn, causes the neurons to fire. Although this may sound similar to the optical neural manipulation made possible by genetically modifying cells, or optogenetics, this material could offer a simpler alternative to studying and modifying neural activity. “There’s no genetics,” Tian explains. “Everything is physical.”

The porous silicon material is a “versatile interface to biology,” says John A. Rogers, an electronic materials expert at the University of Illinois, Urbana-Champaign, who was not involved with the study. The particles “exploit both the excellent electronic properties of silicon and its biocompatible, bioresorbable nature,” he adds.

To create the deformable particles, the team used its homemade chemical vapor deposition system to decompose silane gas. Liberated silicon atoms then congregate in the nanoscopic voids of a mesoporous silicon dioxide template. Within the template, the silicon forms amorphous silicon nanowires. The template also allows nanoscopic bridges to grow between these wires.

After the researchers dissolve the template in hydrofluoric acid, they’re left with microscopic networks of wires and bridges. The gaps in the structures are largely responsible for their sponginess, but the property is boosted by a chemical bonus: Silicon oxidizes in air, which helps the porous particles take on water and become squishier in wet conditions.



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Suresh Mani (June 29, 2016 2:31 PM)
This sounds very interesting. A possible application could be for anodes in lithium ion batteries. Silicon is attractive because of its high capacity but undergoes large expansion and contraction and hence suffers from poor cycle life. The spongy silicon could be excellent if it retains silicons high capacity but has improved cycle life. If you are interested I can provide some consulting service to evaluate your material.


Edward James Morris (June 30, 2016 12:28 AM)
What possibilities are there for the use of spongy silicon for amorphous photoelectric films in solar power generation? The amorphous films in use today are mounted on metallic films and adsorb at three wavelengths to accommodate solar power generation in varying light and weather conditions. I'd be interested if this application would even be feasible. Another application may be firing of spongy silicon into certain nerve cells that would provide limited sight to the blind. Comments, please?
Thomas L Fare (June 30, 2016 8:28 AM)
Years ago, we tried using porous silicon (made by an electrochemical process) for similar applications. We did not have sufficiently good tools to make or characterize, but I would be curious if that technology can now better put to use as an alternative (or a point of comparison). Good luck!

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