Nanolaser biosensor for simple DNA detection

Researchers from Yokohama National University, Japan, have created a photonic crystal nanolaser biosensor capable of detecting the adsorption of biomolecules based on the laser’s wavelength shift. It is believed the work will enable a simple method to sense DNA, as well as potential biomarker proteins of cancer or other diseases such as Alzheimer’s.

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. Professor Toshihiko Baba explained that the team initially focused on wavelength behaviour rather than laser emission intensity, “but quickly noticed that [the laser emission] intensity is influenced by both pH and polymers”.

The team discovered these results when they deposited a protective film of thin zirconium dioxide (ZrO₂) 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.

According to Professor Baba, the nanolaser device can sense surface charge because the surface charge changes the occupancy rate of electrons at the surface states in the semiconductor of the nanolaser, modifying the semiconductor’s emission efficiency. Writing with his colleagues in the journal Applied Physics Letters, he said, “The emission intensity of a GaInAsP photonic crystal nanolaser is affected by the pH of the solution in which the nanolaser is immersed.”

This phenomenon “enables detection of the adsorption of biomolecules from the nanolaser biosensor both in terms of wavelength and intensity”, Professor Baba said. It means the team has become the first group to report the detection of surface charges using photonic sensors, allowing them to examine the details of the biomolecules.

Using laser intensity to detect biomolecules is potentially less expensive than the fluorescent tagging or spectroscopy techniques typically used in biosensors. As the nanolaser biosensor needs neither labels nor spectrometers if it utilises the intensity change, this greatly simplifies detection, which has already been demonstrated in the case of DNA.

Professor Baba said the team’s results were “very reproducible” and they hope to apply the technology to “sensing DNA, biomarker proteins of cancer, Alzheimers, etc, from human bodily fluids such as blood, as a simpler procedure than any others before now”. He noted, “Next we’ll be investigating the sensitivity, selectivity and stability of this phenomenon.

“Our research project, which runs from 2012 to 2016, ultimately targets the development of a photonic crystal nanolaser sensor for biomarker detection,” added Professor Baba. “We’re working to further simplify and improve the sensor so that it will be ready for practical use within a few years.”

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