Biochip measures glucose in saliva, not blood

Engineers at Brown University have designed a biological device that can measure glucose concentrations in human saliva. The technique could eliminate the need for diabetics to draw blood to check their glucose levels. The biochip uses plasmonic interferometers and could be used to measure a range of biological and environmental substances. Results are published in Nano Letters.

PROVIDENCE, R.I. [Brown University] — For the 26 million Americans with diabetes, drawing blood is the most prevalent way to check glucose levels. It is invasive and at least minimally painful. Researchers at Brown University are working on a new sensor that can check blood sugar levels by measuring glucose concentrations in saliva instead.

Tripping the light fantastic Each plasmonic interferometer -thousands of themper square millimeter - consists of a slit flanked by
two grooves etched in a silver metal film. The
schematic shows glucose molecules "dancing" on the
sensor surface illumniated by light with different colors.
Changes in light intensity transmitted through the slit
of each plasmonic interferometer yield information
about the concentration of glucose molecules in solution.Credit: Domenico Pacifici

The technique takes advantage of a convergence of nanotechnology and surface plasmonics, which explores the interaction of electrons and photons (light). The engineers at Brown etched thousands of plasmonic interferometers onto a fingernail-size biochip and measured the concentration of glucose molecules in water on the chip. Their results showed that the specially designed biochip could detect glucose levels similar to the levels found in human saliva. Glucose in human saliva is typically about 100 times less concentrated than in the blood.

“This is proof of concept that plasmonic interferometers can be used to detect molecules in low concentrations, using a footprint that is ten times smaller than a human hair,” said Domenico Pacifici, assistant professor of engineering and lead author of the paper published in Nano Letters, a journal of the American Chemical Society.

The technique can be used to detect other chemicals or substances, from anthrax to biological compounds, Pacifici said, “and to detect them all at once, in parallel, using the same chip.”

To create the sensor, the researchers carved a slit about 100 nanometers wide and etched two 200 nanometer-wide grooves on either side of the slit. The slit captures incoming photons and confines them. The grooves, meanwhile, scatter the incoming photons, which interact with the free electrons bounding around on the sensor’s metal surface. Those free electron-photon interactions create a surface plasmon polariton, a special wave with a wavelength that is narrower than a photon in free space. These surface plasmon waves move along the sensor’s surface until they encounter the photons in the slit, much like two ocean waves coming from different directions and colliding with each other. This “interference” between the two waves determines maxima and minima in the light intensity transmitted through the slit. The presence of an analyte (the chemical being measured) on the sensor surface generates a change in the relative phase difference between the two surface plasmon waves, which in turns causes a change in light intensity, measured by the researchers in real time.

“The slit is acting as a mixer for the three beams — the incident light and the surface plasmon waves,” Pacifici said.

The engineers learned they could vary the phase shift for an interferometer by changing the distance between the grooves and the slit, meaning they could tune the interference generated by the waves. The researchers could tune the thousands of interferometers to establish baselines, which could then be used to accurately measure concentrations of glucose in water as low as 0.36 milligrams per deciliter.

“It could be possible to use these biochips to carry out the screening of multiple biomarkers for individual patients, all at once and in parallel, with unprecedented sensitivity,” Pacifici said.

The engineers next plan to build sensors tailored for glucose and for other substances to further test the devices. “The proposed approach will enable very high throughput detection of environmentally and biologically relevant analytes in an extremely compact design. We can do it with a sensitivity that rivals modern technologies,” Pacifici said.

Tayhas Palmore, professor of engineering, is a contributing author on the paper. Graduate students Jing Feng (engineering) and Vince Siu (biology), who designed the microfluidic channels and carried out the experiments, are listed as the first two authors on the paper. Other authors include Brown engineering graduate student Steve Rhieu and undergraduates Vihang Mehta, Alec Roelke.

The National Science Foundation and Brown (through a Richard B. Salomon Faculty Research Award) funded the research.

- by Richard Lewis

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Brown School of Engineering to Host a One-Day Planetary MicroRover Workshop

On February 16, 2012, MicroRover will be hosted by the Brown University School of Engineering (Barus and Holley Room 190). MicroRover continues our Space Horizons series of intense one-day workshops, this year bringing planetary researchers together with engineering innovators to discuss the design and application of microvehicles to planetary science missions.

The majority of rovers sent to other planets have offered significant mission utility by deploying multiple-instrument packages.  On the other hand, rovers are becoming increasingly large and complex with longer development times and higher engineering costs. This leads directly to greater risk-aversion that easily spirals into even higher costs and increasing risk-aversion.  With so much riding on each mission, 'safe' landing sites must be selected with exceeding care and ongoing operations undertaken with ever-greater caution at every juncture -- thereby limiting exploration opportunities.

Smaller rovers may offer less capability individually, yet may also provide this utility with far less cost and risk exposure, particularly if large numbers are deployed.  In particular, advantages may include:

• Unit costs that are lower due to simpler designs and the economies of higher production volumes.
• More than one point of interest can be studied simultaneously.
• Instruments may be distributed among specialized vehicles that work together.
• Spare rovers can be kept in reserve during a mission, allowing consideration of higher risk operations.
• A larger rover might act as a "mother ship" to transport families of microrovers to new sites of interest.

Through formal presentations, presenter Q & A, expert panels and informal venues, our workshop will stimulate a wide variety of discussions on topics relevant to the subject of microrover development and mission applications.

Participation is limited to 50. There is no formal registration process or fee for students and faculty of Brown University, and we ask only that you contact us ahead of time to ensure that there will be sufficient space.  Planetary researchers and robotics engineers from other institutions are invited to register online. Student sponsorship for overnight accommodation is available to student from other universities with sponsorship from the NASA Rhode Island Space Grant Consortia.

For additional information, please contact: Kenneth_Ramsley@brown.edu  or visit the workshop website at:
http://www.brown.edu/Departments/Engineering/Workshops/Microrover

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Christian Franck wins Haythornthwaite Research Initiation Grant from ASME Applied Mechanics Division

Christian Franck, an assistant professor in the School of Engineering at Brown University, has received a Haythornthwaite Research Initiation Grant, a new divisional award presented by the Applied Mechanics Division (AMD) of the American Society of Mechanical Engineers (ASME).

This new grant targets university faculty that are at the beginning of their academic careers engaged in research in theoretical and applied mechanics. Professor Franck was one of three recipients of the 2011 awards, along with Dennis Kochmann of CalTech and Xuanhe Zhao of Duke. 

“This is a well deserved award for Professor Franck,” said Dean Larry Larson, “and this grant reflects the potential impact of his research program. The mechanics program has been an area of historic strength at Brown and it is one that continues to remain vibrant with bright, young professors such as Professor Franck.”

Professor Franck specializes in biomechanics and new experimental mechanics techniques at the micro and nanoscale. He received his B.S. in aerospace engineering from the University of Virginia in 2003, and his M.S. and Ph.D. from the California Institute of Technology in 2004 and 2008. His doctoral research was on the development of a quantitative three-dimensional experimental technique for applications in soft biomaterials and cellular traction investigations. Dr. Franck held a post-doctoral position at Harvard investigating brain and neural trauma before beginning his appointment at Brown in 2009.

The Robert M. and Mary Haythornthwaite Foundation has been a generous supporter of the ASME Applied Mechanics Division (AMD).  The Foundation supports scientific research, primarily research in the field of theoretical and applied mechanics. Robert Haythornthwaite was founder and first President of the American Academy of Mechanics.

Robert Haythornthwaite, who grew up in England, also had a Brown connection. In 1950, he was award a Commonwealth Fund Fellowship and spent a year studying at Brown. After obtaining his Ph.D. from London University in 1952, he returned to Brown in 1953 to join the Division of Engineering at Brown before moving on to positions at Michigan, Penn State, and Temple.

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