Photonic Crystal Nanolaser Biosensor Simplifies DNA Detection

Top view of the nanolaser; the narrow slot (horizontal line) is the sensor’s main part. The periodic holes form a photonic crystal; the laser’s emission is extracted to the top. (Source: T. Baba, Yokohama NU)

Top view of the nanolaser; the narrow slot (horizontal line) is the sensor’s main part. The periodic holes form a photonic crystal; the laser’s emission is extracted to the top. (Source: T. Baba, Yokohama NU)

A team of Yokohama National University researchers in Japan has created a photonic crystal nanolaser biosensor capable of detecting the adsorption of biomolecules based on the laser’s wavelength shift. Equally impressive, the nanolaser biosensor enables detection of the surface charge from its laser emission intensity, which in turn can also be used to sense the adsorption of biomolecules.
The team was first not  focusing on the intensity of the laser emission because it’s sensitive to the quality of the fabricated laser and they didn’t expect it to show sensing signals. “In the beginning we focused on wavelength behavior, but quickly noticed that [the laser emission] intensity is influenced by both pH and polymers,” noted Toshihiko Baba, a professor in Yokohama National University’s Dept. of Electrical and Computer Engineering. “Our results were very reproducible and, interestingly, we found that the behaviors of the wavelength and intensity are independent.”
Then the team discovered that when they deposited a protective film of thin zirconium dioxide over the device using atomic layer deposition, and then tried sensing in liquids of high or low pH and liquids containing charged polymers. The coating was necessary to protect the nanolaser from damage and unwanted wavelength drift. The nanolaser device can sense surface charge because they change the occupancy rate of electrons at the surface states in the semiconductor of the nanolaser.
So far, the team’s work is the first report of the detection of surface charges using such photonic sensors. Since it involves different physical parameters, the researchers can examine the details of the biomolecules. (Source: Optik & Photonik 1 / 2015)

Referenz: K. Watanabe et al.: Simultaneous detection of refractive index and surface charges in nanolaser biosensors, Appl. Phys. Lett., online 13 January 2015, DOI: 10.1063/1.4904481

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