Biosensors which can selectively detect a very small amount of biomarker protein in human blood are desired toward
early diagnoses of severe diseases. However, no methods simultaneously satisfy the requirements such as high sensitivity, high selectivity, simple detection, and immediacy. We succeeded in detecting ultra-low-concentration streptavidin (SA) even in a highly impure sample using nanoslot photonic crystal (PC) nanolasers. This nanolaser consists of GaInAsP semiconductor slab with a periodic airhole array. Since the total device area is no larger than 20 × 20 μm2, highthroughput fabrication is possible even using e-beam lithography. Moreover, it is easy to operate by photopumping through free-space optics. Since the evanescent wave of the laser mode penetrates from the PC slab, the laser wavelength changes sensitively to the environmental index. In the sensing experiment, we first functionalized the devices with biotin, and then measured the wavelength in ultrapure water before and after immersing in the solutions with various concentrations of SA. As a result, we evaluated that the detection limit of SA is 16 zM. In another experiment, we put 1 μM BSA into the solution as a contaminant, and repeated the same measurement. We detected 100 zM SA even in the impure solution only when biotin is functionalized in advance, meaning a selectivity ratio (BSA / SA) of 1013. Thus this device achieves unprecedentedly high sensitivity and selectivity in addition to the simple fabrication and fast sensing. It is very promising as a point of care device for medical diagnoses.