Sorting cells with sound waves

Acoustic device that separates tumor cells from blood cells could help assess cancer’s spread.

Illustration: Christine Daniloff/MIT

Researchers from MIT, Pennsylvania State University, and Carnegie Mellon University have devised a new way to separate cells by exposing them to sound waves as they flow through a tiny channel. Their device, about the size of a dime, could be used to detect the extremely rare tumor cells that circulate in cancer patients’ blood, helping doctors predict whether a tumor is going to spread.

This microfluidic device uses sound waves to sorts cells as they flow through the channel, from left to right. Image courtesy of the researchers

Separating cells with sound offers a gentler alternative to existing cell-sorting technologies, which require tagging the cells with chemicals or exposing them to stronger mechanical forces that may damage them.

“Acoustic pressure is very mild and much smaller in terms of forces and disturbance to the cell. This is a most gentle way to separate cells, and there’s no artificial labeling necessary,” says Ming Dao, a principal research scientist in MIT’s Department of Materials Science and Engineering and one of the senior authors of the paper, which appears this week in the Proceedings of the National Academy of Sciences.

Subra Suresh, president of Carnegie Mellon, the Vannevar Bush Professor of Engineering Emeritus, and a former dean of engineering at MIT, and Tony Jun Huang, a professor of engineering science and mechanics at Penn State, are also senior authors of the paper. Lead authors are MIT postdoc Xiaoyun Ding and Zhangli Peng, a former MIT postdoc who is now an assistant professor at the University of Notre Dame.

The researchers have filed for a patent on the device, the technology of which they have demonstrated can be used to separate rare circulating cancer cells from white blood cells.

To sort cells using sound waves, scientists have previously built microfluidic devices with two acoustic transducers, which produce sound waves on either side of a microchannel. When the two waves meet, they combine to form a standing wave (a wave that remains in constant position). This wave produces a pressure node, or line of low pressure, running parallel to the direction of cell flow. Cells that encounter this node are pushed to the side of the channel; the distance of cell movement depends on their size and other properties such as compressibility.

However, these existing devices are inefficient: Because there is only one pressure node, cells can be pushed aside only short distances.

The new device overcomes that obstacle by tilting the sound waves so they run across the microchannel at an angle — meaning that each cell encounters several pressure nodes as it flows through the channel. Each time it encounters a node, the pressure guides the cell a little further off center, making it easier to capture cells of different sizes by the time they reach the end of the channel.

ORIGINAL: MIT

Anne Trafton | MIT News Office 

August 25, 2014

Berkeley creates the first graphene earphones, and (unsurprisingly) they’re awesome

ORIGINAL: Berkeley

By Sebastian Anthony

March 13, 2013

Researchers at the University of Berkeley in California have created the first ever graphene audio speaker (earphone). In its raw state, without any kind of optimization, the researchers show that graphene’s superior physical and electrical properties allow for an earphone with frequency response comparable to or better than a pair of commercial Sennheiser earphones.

A loudspeaker (or earphone or headphone) works by vibrating a (usually) paper diaphragm (aka a cone), creating pressure waves in the air around you. Depending on the frequency of these waves, different sounds are created. Human ears, depending on their age, can usually hear frequencies between 20Hz (very low pitch) and 20KHz (very high). Generally, the quality of a speaker is defined by how flat its frequency response is — in other words, whether it produces sounds equally well, no matter where they fall on the 20Hz to 20KHz scale. A poor speaker, or, say, a bassy set of headphones, might be very strong in the lower ranges, but weaker at the top. (See: In search of the perfect headphones.)

In Berkeley’s graphene earphone, the diaphragm is made from a 30nm-thick, 7mm-wide sheet of graphene. This diaphragm is then sandwiched between two silicon electrodes, which are coated with silicon dioxide to prevent any shorting if the diaphragm is driven too hard. By applying power to the electrodes, an electrostatic force is created, which causes the graphene diaphragm to vibrate, creating sound. By oscillating the electricity, different sounds are created.

Graphene earphone frequency response (top), vs. Sennheiser MX-400 earphones (bottom)

Given graphene’s status as a wonder material we shouldn’t really be surprised, but it turns out that this graphene speaker — the first of its kind — has intrinsically excellent performance. As you can see in the graph above, the graphene earphone’s frequency response is superb. The reason for this is down to the graphene diaphragm’s simplicity: Whereas most diaphragms/cones must be damped (padded, restricted) to prevent undesirable frequency responses, the graphene diaphragm requires no damping. This is because graphene is so strong that the diaphragm can be incredibly thin — and thus very light. Instead of being artificially damped, the graphene diaphragm is damped by air itself. As a corollary, the lack of damping means that the graphene diaphragm is also very energy efficient — which could be important for reducing the power usage of smartphone and tablet speakers.

Remember, we are talking about a completely untuned, unoptimized earphone, and yet its frequency response is superior to a magnetic coil speaker that has been the target of decades of research and development. If that wasn’t exciting enough, the researchers say that their method of growing graphene with chemical vapor deposition can easily be scaled to produce larger diaphragms and thus larger speakers. In all likelihood, following some more research, graphene will go on to become the material of choice for studio speakers — and hopefully, cost permitting, consumer speakers and earphones as well.

Now read: Silicene discovered: Single-layer silicon that could beat graphene to market

Research paper: arXiv:1303.2391 - “Electrostatic Graphene Loudspeaker”

Navy to deafen 15,900 whales and dolphins and kill 1,800 more

ORIGINAL: Signon.org/sign/navy-under-water-sound

By Lyndia Storey (Contact)

To be delivered to: U.S. Navy EIS Comments

Stop the killing of 1,800 whales and dolphins and the deafening of 15,900 more by ceasing the operation of the Navy's underwater sound system in the Hawaiian Islands, the California and Atlantic Coasts, and the Gulf of Mexico.

The Navy is required to include comments on their Environmental Impact Statement (EIS) re: the use of high frequency underwater sound for testing in Hawaii, the California and Atlantic Coasts, and the Gulf of Mexico. According to their estimates it will deafen more than 15,900 whales and dolphins and kill 1,800 more over the next 5 years. Whales and dolphins depend on sound to navigate and live. Your signature and comment will have to be included in the EIS and could stop this Naval program, potentially saving the lives of these ocean creatures. The comments must be in by July 10, 2012.

NEW goal - We need 375,000 signatures

There are currently 373,920 signatures