Sensitive on-chip detection of a protein biomarker in human serum and plasma over an extended dynamic range using silicon photonic microring resonators and sub-micron beads

We demonstrate a three-step assay on a silicon photonic microring resonator-based detection platform that enables the quantitation of the cardiac biomarker C-reactive protein (CRP) over a dynamic range spanning six orders of magnitude. Using antibody-modified microrings, we sequentially monitor primary CRP binding, secondary recognition of bound CRP by a biotinylated antibody, and tertiary signal amplification using streptavidin-functionalized beads. This detection methodology is applied to CRP quantitation in human serum and plasma samples.     

Microstructure of annealed low-temperature-grown GaAs layers

The crystal structure and orientation of As precipitates in annealed low-temperature GaAs (LT-GaAs) layers have been investigated by transmission electron microscopy. Three types of As precipitates were identified in layers grown by molecular beam epitaxy at substrate temperatures from 180° to 210° C. In the monocrystalline LT-GaAs layers small pseudocubic As precipitates (2–3 nm diameter) coherent with the GaAs lattice were observed. These precipitates lose their coherency when a certain critical size is exceeded. Precipitates of similar sizes are occasionally found for which a TEM lattice image cannot be obtained. These precipitates are believed to be amorphous. Larger As precipitates with a hexagonal structure (>4 nm diameter) were also found in the layers. These hexagonal As precipitates were observed to be largest near structural defects. The effect of these precipitates on the structure and on the electronic properties of the host GaAs is discussed.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Photonics-on-a-chip: recent advances in integrated waveguides as enabling detection elements for real-world, lab-on-a-chip biosensing applications

By leveraging advances in semiconductor microfabrication technologies, chip-integrated optical biosensors are poised to make an impact as scalable and multiplexable bioanalytical measurement tools for lab-on-a-chip applications. In particular, waveguide-based optical sensing technology appears to be exceptionally amenable to chip integration and miniaturization, and, as a result, the recent literature is replete with examples of chip-integrated waveguide sensing platforms developed to address a wide range of contemporary analytical challenges. As an overview of the most recent advances within this dynamic field, this review highlights work from the last 2-3 years in the areas of grating-coupled, interferometric, photonic crystal, and microresonator waveguide sensors. With a focus towards device integration, particular emphasis is placed on demonstrations of biosensing using these technologies within microfluidically controlled environments. In addition, examples of multiplexed detection and sensing within complex matrices--important features for real-world applicability--are given special attention.     

Stabilized frequency comb with a self-referenced femtosecond Cr:forsterite laser

A frequency comb is generated with a Cr:forsterite femtosecond laser, spectrally broadened through a highly nonlinear optical fiber to span from 1.0 to 2.2 ,m, and stabilized using the f-to-2f self-referencing technique. The repetition rate and the carrier-envelope offset frequency are stabilized to a hydrogen maser, calibrated by a cesium atomic fountain clock. Simultaneous frequency measurement of a 657-nm cw laser by use of the stabilized frequency combs from this Cr:forsterite system and a Ti:sapphire laser agree at the 10(-13) level. The frequency noise of the comb components is observed at 1064, 1314, and 1550 nm by comparing the measured beat frequencies between cw lasers and the supercontinuum frequency combs.