Domenico Pacifici and colleagues, Brown University, Providence, RI, USA, have developed a biochip sensor that can measure glucose in real time with great accuracy and specificity. This is an important step toward a device that would enable diabetics to test their glucose levels without drawing blood.
The biochip is made from a one-inch-square piece of quartz coated with a thin layer of silver. Etched in the silver are thousands of nanoscale interferometers—100 nm wide slits with a 200 nm groove on each side. When light is shined on the chip, the grooves cause a wave of free electrons in the silver—a surface plasmon polariton—to propagate toward the slit. These waves interfere with light that passes through the slit. Sensitive detectors then measure the patterns of interference generated by the grooves and slits.
When a liquid is deposited on the chip, the light and the surface plasmon waves propagate through that liquid before they interfere with each other. This alters the interference patterns depending on the chemical makeup of the liquid. By adjusting the distance between the grooves and the center slit, the interferometers can be calibrated to detect the signature of specific compounds or molecules, with high sensitivity in extremely small sample volumes.
The researchers added two enzymes that react with glucose to the liquid: Glucose oxidase reacts with glucose to form hydrogen peroxide. This then reacts with horseradish peroxidase to generate resorufin, which can absorb and emit red light, thus coloring the solution. The researchers could then tune the interferometers to look for the red resorufin molecules.
After having detected glucose in artificial saliva, a mixture of water, salts and enzymes, the next step is to start testing the method in real human saliva. According to the researchers, the methode could also detect toxins in air or water or monitor chemical reactions as they occur at the sensor surface in real time.
- A ‘plasmonic cuvette’: dye chemistry coupled to plasmonic interferometry for glucose sensing,
Vince S. Siu, Jing Feng, Patrick W. Flanigan, G. Tayhas R. Palmore,
Nanophotonics 2014, 3 (3).