A laser biosensor has demonstrated a simpler way to identify DNA and biomarker proteins via changes in a solution’s surface charge density or pH. A team from Yokohama National University developed the GaInAsP photonic crystal nanolaser biosensor, which can detect the absorption of biomolecules based on the laser’s wavelength shift and intensity. This method is potentially less expensive to perform than fluorescent tagging or spectroscopy techniques. The researchers deposited a protective film of 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 protects the nanolaser from damage and unwanted wavelength drift. A GaInAsP photonic crystal nanolaser biosensor, the main component of which is the center narrow slot (horizontal line). The periodic holes, which form a photonic crystal, have been intentionally modified so the laser's emission is effectively extracted to the top. Courtesy of Toshihiko Baba/Yokohama National University. The researchers found that the nanolaser could function as a sensor because changes to the surface charge in the solution altered the laser’s emission efficiency. This also allows the nanolaser to “simultaneously and independently detect the refractive index and electric charges near the surface on the basis of the variation in emission wavelength and intensity, respectively,” the researchers wrote in a study published in Applied Physics Letters (doi: 10.1063/1.4904481). “In the beginning we focused on wavelength behavior, but quickly noticed that (the laser emission) intensity is influenced by both pH and polymers,” said professor Dr. Toshihiko Baba. “Our results were very reproducible and, interestingly, we found that the behaviors of the wavelength and intensity are independent.” The researchers are now working to apply their method to “sensing DNA, biomarker proteins of cancer, Alzheimer’s, etc., from human bodily fluids such as blood.” “Next we’ll be investigating the sensitivity, selectivity and stability of this phenomenon,” Baba said. “If these issues can be cleared, it will move another step toward practical use. We're working to further simplify and improve the sensor so that it will be ready for practical use within a few years.” This four-year research project, which extends through 2016, is funded by Japan’s Ministry of Education, Culture, Sports, Science and Technology. For more information, visit www.ynu.ac.jp.