System Bits: Nov. 25

Biological circuits
In recent years, researchers have made progress in the design and creation of biological circuits which can take a number of different inputs and deliver a particular kind of output — like electronic circuits. However, while individual components of such biological circuits can have precise and predictable responses, those outcomes become less predictable as more such elements are combined. Now, MIT researchers have come up with a way of greatly reducing that unpredictability, introducing a device that could ultimately allow such circuits to behave nearly as predictably as their electronic counterparts.

There are many potential uses for such synthetic biological circuits, the team explained, including biosensing — cells that can detect specific molecules in the environment and produce a specific output in response. For example, cells that could detect markers that indicate the presence of cancer cells, and then trigger the release of molecules targeted to kill those cells.

It is important for such circuits to be able to discriminate accurately between cancerous and noncancerous cells, so they don’t unleash their killing power in the wrong places. To do that, robust information-processing circuits created from biological elements within a cell become highly critical.

The device the team produced to address that problem is called a load driver, and its effect is similar to that of load drivers used in electronic circuits: It provides a kind of buffer between the signal and the output, preventing the effects of the signaling from backing up through the system and causing delays in outputs.

While this is relatively early-stage research that could take years to reach commercial application, the concept could have a wide variety of applications, the researchers said. For example, it could lead to synthetic biological circuits that constantly measure glucose levels in the blood of diabetic patients, automatically triggering the release of insulin when it is needed.

Nanoantennas for ultra-high density magnetic storage
Researchers at Nano-Meta Technologies Inc. in the Purdue Research Park have shown how to overcome critical limitations of a material that could enable magnetic storage technology to achieve data-recording densities.

The researchers aid the new technology could make it possible to record data on an unprecedented small scale using tiny “nanoantennas” and to increase the amount of data that can be stored on a standard magnetic disk by 10 to 100 times.

The storage industry’s technology strategy, called heat-assisted magnetic recording (HAMR), is based on the design of the nanoantenna, or near-field transducer (NFT). HAMR harnesses “plasmonics,” which uses clouds of electrons called surface plasmons to manipulate and control light.

But some of the plasmonic NFTs under development rely on metals such as gold and silver, which are not mechanically robust and present a challenge in fabrication and long-term reliability of the HAMR recording head.

The researchers are working to replace gold with titanium nitride. since it offers high strength and durability at high temperatures, and its use as a nanoantenna paves the way for next-generation recording systems.

They have also modified the physical properties of titanium nitride, tailoring it for HAMR.

They believe this technology could make it possible to circumvent the disk-storage-capacity limits imposed by conventional magnetic recording materials. Normally, lenses cannot focus light smaller than the wavelength of the light itself, which is hundreds of nanometers across. However, nanoantennas allow light to be focused into spots far smaller than the wavelength of light, making it possible to increase the storage capacity of the medium.