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SSPMs fabricated using CMOS technology consisting of arrays of 30- and 50- [micro]m square pixels in 1.5 mm x 1.5 mm total area with high, 61%, and low, 29%, fill factors (packing density) were used to measure the photon intensity resolution for a pulsed laser light source. Different sources of noise (i.e., cross talk, dark counts, and electronic) have a deleterious effect on the energy resolution, and this work looks at the relative sizes of these contributions. Even though noise effects increase with larger fill factors and active area, this work examines the trade-off between these noise terms and the improvement in the detection efficiency with increased excess bias or fill factor. The energy resolutions from various gamma rays, including 122 keV, 511 keV, 662 keV, and 1275 keV, measured with an LYSO scintillation crystal (1.5 mm x 1.5 mm x 3 mm) were compared to the pulsed laser results to examine all noise contributions to the energy resolution. The SSPM response can be described by a binomial function. When greater than 70% of the pixels are triggered, the energy resolution contains a substantial contribution from the detector response that arises from a binomial detector response of the SSPM, which contains a finite number of pixel elements. Index Terms--Complementary metal-oxide semiconductor (CMOS), LYSO, SiPM, solid-state photomultipler, solid-state photomultiplier (SSPM).

The performance of CMOS avalanche photodiode pixels operated in a Geiger mode, wherein the pixels, called Geiger photodiode (GPD) pixels, convert an incident analog photon flux into a digital count rate is examined. It is seen that the noise-equivalent illumination exhibits a minimum of 300 Hz at an operating voltage of 28 V and the best operating voltage for the GDP pixel increases from 28V with increasing signal intensity.

Research has been conducted on the dioxygen bound state of cytochrome P450 (sub)cam mutant. The results of the resonance Raman and electronic paramagnetic resonance studies of this mutant and its complex with reduced putidaredoxin are discussed.

Results show that water enters the heme pocket of the nitric oxide bound horse heart metmyoglobin following the dissociation of nitric oxide. Data reveal that water binds to the heme iron and eventually gets displaced when nitric oxide undergoes bimolecular rebinding with histidine-64 playing a role in the process.

An Fe-O-O bending mode in oxycytochrome P450cam was identified through resonance Raman spectroscopy. The identification of this bending mode has structural implications for enzyme function since its frequency reflects the energies associated with Fe-O-O distortion in oxyhemeprotein active sites. Results also suggested a strain in the Fe-O-O linkage in camphor-bound oxyP450cam which could be important for catalytic coupling.

Resonance Raman spectroscopy and optical absorption studies were used to investigate the effect of Pd on the heme active site of ferric camphor-bound P450cam. Putidaredoxin binding were found to affect the distal side of the P450cam and permits water entry into the heme pocket. Results reveal that the electrostatic shielding of charged groups on the proximal face of P450cam will be observed when putiredoxin binds and contributes to the observed upshift of the Fe-S mode.

The laser photolysis and time-resolved Raman spectroscopy of CO-bound H93G myoglobin (Mb) mutants are used to investigate the influence of the proximal ligand on the CO rebinding kinetics. The measurements indicate that perturbations associated with the proximal heme ligand can dramatically influence the diatomic ligand rebinding kinetics.

Interactions of Li+, Na+, and K+ with C60 molecules have been studied over the collision energy range from 0 to 150 eV. For Li+ and Na+, insertion of the alkali to form the endohedral [Li[ATOTHER]@xa[/ATOTHER]C60]+ and [Na[ATOTHER]@xa[/ATOTHER]C60]+ species is observed, with appearance energies of ∼6 and ∼18 eV, respectively. At higher collision energies several processes are observed. For Na+, the hot [Na[ATOTHER]@xa[/ATOTHER]C60]+ appears to relax mainly by loss of C2 units from the fullerene cage, yielding [Na[ATOTHER]@xa[/ATOTHER]C60-2n]+. For [Li[ATOTHER]@xa[/ATOTHER]C60]+, escape of Li+ dominates over C2 loss. For K+, very little [K[ATOTHER]@xa[/ATOTHER]C60]+ is observed, and the main endohedral species observed are fragments [K[ATOTHER]@xa[/ATOTHER]C60-2n]+ (n=1–7), which begin to appear at ∼40 eV. Pure fullerene fragment ions (C60-2n+) are also observed, with cross sections that increase sharply at ∼30 eV for all three projectile ions. These ions are believed to result primarily from thermionic emission of collisionally excited neutrals. For K+, we also examined collisions with C70, obtaining results similar to those for C60. Changes in the endohedral insertion mechanism with projectile size are discussed, as is the competition between C2 evaporation, thermionic emission, and IR emission. [ABSTRACT FROM AUTHOR]

Interaction of Ne+ with C60 has been studied for collision energies ranging up to 100 eV. The dominant process is charge transfer, with C60+ accounting for 85% to 100% of the total product signal in this energy range. At 25 eV collision energy, C60-2n+ dissociative charge transfer products appear, accounting for ∼13% of the total product signal at high energies. At ∼25 eV, NeC60+, NeC58+, and NeC56+ all appear together, followed by a series of NeC60-2n+ products where n increases with increasing collision energy. These products are believed to be endohedral complexes, Ne[ATOTHER]@xa[/ATOTHER]C60-2n+, where neon is physically trapped inside the fullerene cage. The production efficiency of the endocomplexes reaches a maximum of ∼1.2% at 60 eV, and decreases to 0.5% at 100 eV. Modeling the results leads to the following picture of Ne++C60 collision dynamics: Charge transfer occurs in nearly all collisions, and is the only significant process for high impact parameters. At collision energies below ∼25 eV, translational-to-internal energy transfer is inefficient, even for low impact parameter collisions. At higher energies, the inelasticity jumps to near 100%, leading to fragmentation of the nascent products. Both endohedral penetration and efficient energy transfer appear to require bond rupture in the C60. [ABSTRACT FROM AUTHOR]

We report measurements of C60-2nNe+ and C+60-2n formation in collisions of Ne+ with C60 over a range from 2–212 eV (CM). Activation energies and crude angular information are given for each channel. Endohedral complex formation and fragmentation both require low impact parameter collisions, while charge transfer can occur with larger impact parameters as well. [ABSTRACT FROM AUTHOR]

This paper describes a prototype of an integrated fluorescence detection system that uses a microavalanche photodiode ([micro]APD) as the photodetector for microfluidic devices fabricated in poly(dimethylsiloxane) (PDMS). The prototype device consisted of a reusable detection system and a disposable microfluidic system that was fabricated using rapid prototyping. The first step of the procedure was the fabrication of microfluidic channels in PDMS and the encapsulation of a multimode optical fiber (100-[micro]m core diameter) in the PDMS; the tip of the fiber was placed next to the side wall of one of the channels. The optical fiber was used to couple light into the microchannel for the excitation of fluorescent analytes. The photodetector, a prototype solid-state [micro]APD array, was embedded in a thick slab (1 cm) of PDMS. A thin (80 [micro]m) colored polycarbonate filter was placed on the top of the embedded [micro]APD to absorb scattered excitation light before it reached the detector. The [micro]APD was placed below the microchannel and orthogonal to the axis of the optical fiber. The close proximity (~200 [micro]m) of the [micro]APD to the microchannel made it unnecessary to incorporate transfer optics; the pixel size of the [micro]APD (30 [micro]m) matched the dimensions of the channels (50 [micro]m). A blue light-emitting diode was used for fluorescence excitation. The [micro]APD was operated in Geiger mode to detect the fluorescence. The detection limit of the prototype (~25 nM) was determined by finding the minimum detectable concentration of a solution of fluorescein. The device was used to detect the separation of a mixture of proteins and small molecules by capillary electrophoresis; the separation illustrated the suitability of this integrated fluorescence detection system for bioanalytical applications.

In reconstructive surgery, the ability to detect blood flow interruptions to grafted tissue represents a critical step in preventing postsurgical complications. We have developed and pilot tested a compact, fiber-based device that combines two complimentary modalities—diffuse correlation spectroscopy (DCS) and diffuse reflectance spectroscopy—to quantitatively monitor blood perfusion. We present a proof-of-concept study on an in vivo porcine model (n=8). With a controllable arterial blood flow supply, occlusion studies (n= 4) were performed on surgically isolated free flaps while the device simultaneously monitored blood flow through the supplying artery as well as flap perfusion from three orientations: the distal side of the flap and two transdermal channels. Further studies featuring long-term monitoring, arterial failure simulations, and venous failure simulations were performed on flaps that had undergone an anastomosis procedure (n= 4). Additionally, benchtop verification of the DCS system was performed on liquid flow phantoms. Data revealed relationships between diffuse optical measures and state of occlusion as well as the ability to detect arterial and venous compromise. The compact construction of the device, along with its noninvasive and quantitative nature, would make this technology suitable for clinical translation. [ABSTRACT FROM AUTHOR]

The Fe-CO unit in heme proteins has acted as a sensitive structural probe of the heme active site. Detailed information about protein-ligand interactions were obtained through measurement of C-O stretching (vC-o), Fe-CO stretching (vFe-Co) and Fe-C-O bending (delta FeCO) frequencies. RR spectroscopic evidence indicates a hydrogen bond in the A1 conformation of MbCO, implying that a proton exists and contributes to the raised vFE-CO and decreased vC-o.