To chemists, carbon is just carbon. But graphene, the ultrathin material whose strength, flexibility, and high conductivity is promising for electronics, is one of the more costly forms of the element. High quality graphene is commonly made by growing it from expensive, pure carbon-containing gases inside a reaction chamber. In a paper published online in the journal ACS Nano, chemists at Rice University describe using dirty, cheap sources of carbon instead, including insects, plastic, and dog excrement. They even invited a troop of Girl Scouts into the lab to make some graphene from cookies, as seen in the video below:

Last week another TR editor and I were talking about how we didn't know about engineering careers when we were kids. It melts my heart to see these girls visiting the labs established by Richard Smalley, one of the discoverers of fullerenes, the class of carbon materials that includes nanotubes and graphene. One box of cookies, they learned, can be made into $15 billion worth of graphene.

Perhaps the Girl Scouts organization should make a nanotech badge that looks like a buckyball?

This Tuesday at the Materials Research Society spring meeting in San Francisco I sat down with Zhong Lin Wang, director of the center for nanostructure characterization at Georgia Tech. We featured Wang's work on self-powered nanosensors in our "10 Emerging Technologies" issue last year. The payoff from this concept would be huge: nanoscale sensors are exquisitely sensitive, very frugal with power, and, of course, tiny. They could be useful for detecting molecular signs of disease in the blood, minute amounts of poisonous gases in the air, and trace contaminants in food. Eliminating the batteries needed to drive these devices would make it possible to fully miniaturize them.

Wang has been developing devices based on nanowires that exhibit piezoelectricity. That is, they generate a voltage when they're bent. He has been integrating these nanowires into devices that can harvest energy from biomechanical motion--including the running movements of a hamster on a wheel or the tapping of a finger--and use it to power a small sensor.

The problem with these devices has been getting a significant voltage out of them. This Tuesday morning, Wang presented recent data showing he has boosted the voltage produced by his nanowire devices by two orders of magnitude. The new design integrates millions of piezoelectric zinc-oxide nanowires in layered arrays on a plastic backing. Wang has coupled these devices with pH and UV-light sensors and demonstrated that they can power the sensor to take a measurement when stressed. Earlier this month, in the journal Nature, Wang reported a flexible device that produces 1.2 volts when it's stressed; he says he has now made devices that produce 2.4 volts. This is enough to start thinking about integrating a charge-storage device that will make it possible to regulate the voltage going into the sensors for better control of measurements. Indeed, Wang says, that's his next step.

Wang says he proposed the idea of self-powered nanotechnology based on these energy-harvesting devices in 2006, and at the time, there were many skeptics. Now others have started to replicate his results and other groups in academia and even at Samsung are starting their own research in the area.

This device uses magnetic fields to separate cells by size and shape. Credit: Hur Koser

Researchers at Yale have demonstrated a device that uses a magnetic liquid to separate blood cells based on their size and shape in just minutes.

The device applies a magnetic field to a liquid containing magnetic nanoparticles. The nanoparticles create waves that carry cells along depending on their size, shape and mechanical properties. The researchers, led by electrical engineering professor Hur Koser, hope to develop a cheap alternative to cell-sorting techniques that are time-consuming and sometimes require expensive labeling.

Liquid suspensions of magnetic particles, called ferrofluids, are already used as industrial lubricants and in loudspeakers and computer hard disks. These liquids typically contain other chemicals to keep the particles from clumping together and from coming out of the suspension. Magnetic nanoparticles are also being explored for cancer therapies and as contrast agents for magnetic resonance imaging (MRI)--both applications that require very low concentrations.

But the Yale group is the first to make a high-concentration, biocompatible ferrofluid that doesn't contain any chemicals that are harmful to cells, yet still keeps the particles afloat. "It was very tricky to find the parameters to maintain live cells," says Koser.

In experiments described this week in the Proceedings of the National Academy of Sciences, the Yale researchers made microfluidic channels lined with magnetic-field-generating electrodes. Cells were then added to a ferrofluid in the channel. When magnetic fields were applied along the device, the particles in the fluid pushed the cells along the channel, separating them by size and shape. Something similar can be accomplished using electrical fields, says Koser, but this can damage the cells. His group used the device to separate live blood cells from sickle cells and bacteria.

Koser believes the device could be especially helpful when trying to detect very rare types of blood cell, such as cancerous ones. Rapidly sorting cells using magnetic fields could improve the sensitivity of tests for these rare cells without adding any costly chemical labels. Tumor cells are squishier than healthy ones--possibly because they grow quickly and so don't form a proper internal cell skeleton--and Koser hopes that magnetic fields will also be able to separate cells based on their elasticity and other mechanical properties.

"The next step is to try this in conjunction with existing sensors to improve their sensitivity and cut down on time," says Koser.

In the video below, a magnetic field creates waves in a liquid containing magnetic nanoparticles (the nanoparticles are not visible) to separate two types of microbeads based on their size.