By cascading multiple GaInAsSb active regions, the authors have fabricated 2.4μm light-emitting diodes that, for a given light output, operate at reduced current and higher voltage, which can be advantageous for battery-powered sensor applications. Tunnel heterojunctions separating emission regions add no measurable series resistance. Devices are demonstrated at room temperature with continuous wave output.

We report on the growth, processing, and characterization of uncoated, unpassivated GaInAsSb detector mesa photodiodes with a cutoff wavelength of 2.4 μm. We find peak room temperature specific detectivity value of 6×1010 cm Hz1/2/W and maximum zero-bias resistivity of 25 Ω cm2. The zero-bias resistivities of mesas with areas ranging from 502 μm2 to 1 mm2 were found to be limited by generation-recombination currents at mesa sidewalls. At low temperatures, devices were limited by Ohmic leakage, which is likely due to the formation of oxides on the sidewalls. After 6 months of aging, Ohmic leakage becomes the limiting factor at room temperature as well. Based on experimentally obtained material parameters in this and other studies, an upper limit D∗ and R0A were estimated for GaInAsSb materials and compared to those HgCdTe and InGaAs.

Tight control of blood glucose levels has been shown to dramatically reduce the long-term complications of diabetes. Current invasive technology for monitoring glucose levels is effective but underutilized by people with diabetes because of the pain of repeated finger-sticks, the inconvenience of handling samples of blood, and the cost of reagent strips. A continuous glucose sensor coupled with an insulin delivery system could provide closed-loop glucose control without the need for discrete sampling or user intervention. We describe an optical glucose microsensor based on absorption spectroscopy in interstitial fluid that can potentially be implanted to provide continuous glucose readings. Light from a GaInAsSb LED in the 2.2-2.4 µm wavelength range is passed through a sample of interstitial fluid and a linear variable filter before being detected by an uncooled, 32-element GaInAsSb detector array. Spectral resolution is provided by the linear variable filter, which has a 10 nm band pass and a center wavelength that varies from 2.18-2.38 µm (4600-4200 cm −1 ) over the length of the detector array. The sensor assembly is a monolithic design requiring no coupling optics. In the present system, the LED running with 100 mA of drive current delivers 20 nW of power to each of the detector pixels, which have a noise-equivalent-power of 3 pW/Hz 1/2 . This is sufficient to provide a signal-to-noise ratio of 4500 Hz 1/2 under detector-noise limited conditions. This signal-to-noise ratio corresponds to a spectral noise level less than 10 µAU for a five minute integration, which should be sufficient for sub-millimolar glucose detection.

Background-Delirium is associated with a host of negative outcomes, including increased risk of mortality, longer hospital stay, and poor long-term cognitive function. The pathophysiology of delirium is not well understood. Cancer patients undergoing a bone marrow transplant (BMT) are at high risk for developing delirium and Proton Magnetic Resonance Spectroscopy ( 1 H-MRS) could lead to better understanding of the delirium process.Methods-Fourteen BMT patients and 10 controls completed 1 H-MRS, positioned above the corpus callosum, shortly after delirium onset or at study end if no delirium occurred.Results-In the BMT-delirium group, statistically significantly elevated tCho/tCr was found in contrast to the BMT-no delirium group (p<0.05). The BMT-delirium group also showed statistically significantly lesser NAA/tCho compared to both controls (p=0.01) and the BMT-no delirium group (p=0.04).Conclusions-Elevated choline and reduced NAA indicate inflammatory processes and white matter damage as well as neuronal metabolic impairment. Further research is needed to separate the choline peaks, as well as more detailed collection of medication regimens to determine whether a higher choline concentration is a function of the delirium process or cancer treatment effects.