Shota Otsuka

Super-sensitivity in label-free protein sensing using a nanoslot nanolaser

Microphotonic sensors have been actively studied with increasing demands for label-free biosensing in medical diagnoses and life sciences. For high-throughput and low-cost sensing, a high sensitivity is crucial for eliminating the pre-concentration process, while a simple setup of sensors is also desirable. This paper demonstrates a super-sensitivity for protein, which satisfies these requirements. The key device is a photonic crystal nanolaser, in particular with a nanoslot. Even using a simple setup, the nanolaser achieves an extraordinary-low detection limit for BSA protein, i.e. 255 fM on an average, which cannot be explained by its bulk index sensitivity. The specific adsorption of the protein is observed only around the nanoslot with strong laser intensity. This suggests that the super-sensitivity arises from the effective trapping of protein in the nanoslot.

Selective detection of sub-atto-molar Streptavidin in 10 13 -fold impure sample using photonic crystal nanolaser sensors

Biosensors selectively detecting a very small amount of biomarker protein in human blood are desired for early and reliable diagnoses of severe diseases. This paper reports the detection of protein (streptavidin: SA) in ultra-low concentration, with an ultra-high selectivity against contaminants, using photonic crystal nanolasers. For biotin-modified nanolasers in pure water with SA, an extremely-low detection limit of 16 zM is evaluated. Even in a mixture with 1 μM bovine serum albumin as the contaminant, 100 zM SA is detected, meaning a selectivity of 10(13). These are remarkable capabilities that are promising for practical biosensing in the medical applications mentioned above.

Photonic Crystal Point-Shift Nanolasers With and Without Nanoslots—Design, Fabrication, Lasing, and Sensing Characteristics

GaInAsP photonic crystal point-shift nanolasers operate at room temperature under pulsed and continuous-wave condition by photopumping with an effective threshold of ~1 μW, a single-mode peak of over 40 dB, and a small modal volume of ~0.2 times the cubic wavelength. We report the details of its design, fabrication process, measurement method, and lasing characteristics. In particular, we reveal that wide spectral broadening often observed for nanolasers under pulsed condition is caused by large thermal chirping. Then, we focus on a nanolaser-based liquid index sensor that is also applicable to detecting gases and biomolecules. The dependence of the lasers sensitivity and resolution on the modal profile and spectral linewidth are investigated. We also configure the laser in a large-scale array and demonstrate spectrometer-free sensor system. Finally, we present a nanoslot (NS) nanolaser that is particularly suitable for further reducing the modal volume and enhancing light-matter interaction and sensor performance. Additionally, we demonstrate the high sensitivity and spectral narrowing by the unique optical confinement in the NS.

Sub-100 μm Photonic Crystal Si Optical Modulators: Spectral, Athermal, and High-Speed Performance

We report on our recent progress on Si Mach-Zehnder modulators (MZMs) incorporating sub-100 μm slow-light photonic crystal waveguide (PCW) phase-shifters. In the standard MZM with a PCW in each of the arms, we study the power-dependent bit-error-rate (BER) characteristics at 10 Gb/s, and measure BER = 1 × 10^-9 and 1 × 10^-8 even with phase-shifter lengths of 90 and 50 μm, respectively. Furthermore, by exploiting the low-dispersion slow-light in the 90 μm device, we measure a spectral operating bandwidth of 16.9 nm and temperature tolerance between 19-124°C, where the eye pattern amplitude is consistent to within ±25%. In the device with a 90 μm PCW in only one of the MZM arms, designed for large-n_g operation, we achieve BER = 1 × 10^-9 at 10 Gb/s and also observed barely but open eye patterns at 25 and 40 Gb/s.

Photonic crystal nanolasers with nanoslot structure for sensing applications

High-performance and low-cost sensors are critical devices for high-throughput analyses of bio-samples in medical diagnoses and life sciences. In this paper, we demonstrate photonic crystal nanolaser sensor, which detects the adsorption of biomolecules from the lasing wavelength shift. It is a promising device, which balances a high sensitivity, high resolution, small size, easy integration, simple setup and low cost. In particular with a nanoslot structure, it achieves a super-sensitivity in protein sensing whose detection limit is three orders of magnitude lower than that of standard surface-plasmon-resonance sensors. Our investigations indicate that the nanoslot acts as a protein condenser powered by the optical gradient force, which arises from the strong localization of laser mode in the nanoslot.

Selective detection of sub-atto-molar streptavidin in 10^13 fold impure sample using nanoslot photonic crystal nanolaser

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.

Photonic crystal nanoslot nanolaser for ultra-high sensitivity and selectivity protein sensing

GaInAsP photonic crystal nanoslot nanolaser with strong mode localization was used for specific detection of streptavidin. A record low detection limit of 16 zM and an ultra-high selectivity of 1012 against high-concentration contaminants were observed.

Photonic crystal nanoslot nanolaser for super-sensitivity bio-sensing

High-performance and low-cost sensors are critical devices for high-throughput analyses of bio-samples in medical diagnoses and life sciences. This report demonstrates GaInAsP photonic crystal nanolaser sensor, which detects the adsorption of bio-molecules from the lasing wavelength shift. It is a promising device, which balances a high sensitivity, high resolution, small size, easy integration, simple setup and low cost. In particular with a nanoslot structure, it achieves a super-sensitivity in protein sensing whose detection limit is 3-5 orders of magnitude lower than that of standard surface-plasmon-resonance sensors, e.g. ~ 100 fM order for BSA and <; 1 aM for streptavidin. Our investigations suggest a candidate mechanism that the nanoslot acts as a protein condenser powered by the optical gradient force, which arises from the strong localization of laser mode in the nanoslot.