12-01 :: January 2012
nanotimes News in Brief
ngineers at Brown University have designed a biological device that can measure glucose
concentrations in human saliva. The biochip uses plasmonic interferometers and could be used to measure a range of biological and environmental substances. The engineers at Brown etched thou- sands 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 interfero- meters can be used to detect molecules in low con- centrations, using a footprint that is ten times smaller than a human hair,” said Domenico Pacifici, assistant professor of engineering. 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 100nm wide and etched two 200nm-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 po- lariton, 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 sur- face plasmon waves, which in turns causes a change in light intensity, measured by the researchers in real time.
Jing Feng, Vince S. Siu, Alec Roelke, Vihang Mehta, Steve Y. Rhieu, G. Tayhas R. Palmore, and Domenico Pacifici: Nanoscale Plasmonic Interferometers for Multispectral, High-Throughput Biochemical Sensing, In: Nano Letters ASAP, December 26, 2011, DOI:10.1021/nl203325s: http://dx.doi.org/10.1021/nl203325s