pH-sensitive GaInAsP photonic crystal fractal band-edge laser.

The light emission characteristics of GaInAsP semiconductors in aqueous solutions are modified by the surface charge, depending on the balance between radiative and nonradiative recombination. This Letter demonstrates the application of a GaInAsP photonic crystal band-edge laser in sensing a solution pH, which reflects the surface charge. The sensitivity is enhanced by a hybrid of fractal honeycomb and close-packed structures with a large surface-to-volume ratio and a high quality factor (), which allows a low threshold carrier density.

Ion-sensitive photonic-crystal nanolaser sensors.

In general, biochemical sensors based on photonic cavities are used to detect changes in the refractive index of the environment. In this study, however, a GaInAsP semiconductor photonic-crystal nanolaser sensor that we recently developed was found to detect not only the environmental refractive index but also the surface charge. In contrast to the pH sensitivity we reported previously, this is an ultra-sensitive detection mechanism capable of identifying proteins and deoxyribonucleic acids (DNA) at a femtomolar-order or lower concentrations.