InAs/InAsSb Type-II Strained-Layer Superlattice Infrared Photodetectors.

The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) has emerged in the last decade as a viable infrared detector material with a continuously adjustable band gap capable of accommodating detector cutoff wavelengths ranging from 4 to 15 µm and beyond. When coupled with the unipolar barrier infrared detector architecture, the InAs/InAsSb T2SLS mid-wavelength infrared (MWIR) focal plane array (FPA) has demonstrated a significantly higher operating temperature than InSb FPA, a major incumbent technology. In this brief review paper, we describe the emergence of the InAs/InAsSb T2SLS infrared photodetector technology, point out its advantages and disadvantages, and survey its recent development.

Circulating tumor cells: clinically relevant molecular access based on a novel CTC flow cell.

BACKGROUND: Contemporary cancer diagnostics are becoming increasing reliant upon sophisticated new molecular methods for analyzing genetic information. Limiting the scope of these new technologies is the lack of adequate solid tumor tissue samples. Patients may present with tumors that are not accessible to biopsy or adequate for longitudinal monitoring. One attractive alternate source is cancer cells in the peripheral blood. These rare circulating tumor cells (CTC) require enrichment and isolation before molecular analysis can be performed. Current CTC platforms lack either the throughput or reliability to use in a clinical setting or they provide CTC samples at purities that restrict molecular access by limiting the molecular tools available. METHODOLOGY/PRINCIPAL FINDINGS: Recent advances in magetophoresis and microfluidics have been employed to produce an automated platform called LiquidBiopsy®. This platform uses high throughput sheath flow microfluidics for the positive selection of CTC populations. Furthermore the platform quantitatively isolates cells useful for molecular methods such as detection of mutations. CTC recovery was characterized and validated with an accuracy (<20% error) and a precision (CV<25%) down to at least 9 CTC/ml. Using anti-EpCAM antibodies as the capture agent, the platform recovers 78% of MCF7 cells within the linear range. Non specific recovery of background cells is independent of target cell density and averages 55 cells/mL. 10% purity can be achieved with as low as 6 CTCs/mL and better than 1% purity can be achieved with 1 CTC/mL. CONCLUSIONS/SIGNIFICANCE: The LiquidBiopsy platform is an automated validated platform that provides high throughput molecular access to the CTC population. It can be validated and integrated into the lab flow enabling CTC enumeration as well as recovery of consistently high purity samples for molecular analysis such as quantitative PCR and Next Generation Sequencing. This tool opens the way for clinically relevant genetic profiling of CTCs.

Dual interband cascade laser based trace-gas sensor for environmental monitoring.

The development of an interband cascade laser (ICL) based spectroscopic trace-gas sensor for the simultaneous detection of two atmospheric trace gases is reported. The sensor performance was evaluated using two ICLs capable of targeting formaldehyde (H2CO) and ethane (C2H6). Minimum detection limits of 3.5 ppbV for H2CO and 150 pptV for C2H6 was demonstrated with a 1 s integration time. The sensor was deployed for field measurements of H2CO, and laboratory quantification of both formaldehyde and ethane are reported. A cross comparison of the atmospheric concentration data for H2CO with data collected by a collocated commercial H2CO sensor employing Hantzsch reaction based fluorometric detection was performed. These results show excellent agreement between these two different approaches for trace-gas quantification. In addition, laboratory experiments for dual gas quantification show accurate, fast response with no crosstalk between the two gas channels.

Multiwavelength discrimination and measurements of a two-gas mixture by use of a broadly tunable mid-infrared semiconductor laser.

Spectroscopic detection of gases can be achieved by measuring a few species-specific absorption lines, requiring very accurate wavelength control. Alternatively, it can be achieved by using many wavelengths spread over a wide range; each wavelength need not be optimal spectroscopically, but all collectively form a unique fingerprint for the species of interest. Statistical regression can be used to quantify their concentrations. An experimental evaluation of this concept involved using a 3.1 microm broadly tunable Sb-based mid-IR laser to discriminate and measure mixtures of acetylene and water vapor with absorption spectral overlaps. As many as 30 wavelengths from approximately 3200 to approximately 3280 cm-1 were used to measure 5 x 5 combinations of the two-gas concentration. Statistical analysis of the results validates the concept. Each gas concentration was consistently and reliably measured without any problem of interference from the other. In addition, the method was sufficiently sensitivite to detect unusual discrepancies by use of statistical analysis. Optimization of the system's detection capability and its receiver-operating characteristics is demonstrated. The results suggest that the statistical multiwavelength broadband approach to detection of gas mixture can be a highly effective alternative to species-specific single-line spectroscopy.