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Sapsford K.E.,U.S. Food and Drug Administration | Algar W.R.,George Mason University | Algar W.R.,University of British Columbia | Berti L.,University of California at Davis | And 6 more authors.
Chemical Reviews | Year: 2013

Bionanotechnology has now become firmly established in its own right as one of the principle and focused subdisciplines within nanotechnology. Bionanotechnology can be defined as a field representing all facets of research at the intersection of biology and nanomaterials (NM) and is generally characterized as having two somewhat opposite functional goals. The interest in using NMs, and especially NPs, as part of biomolecular composites arises from the unique size-dependent physical, optical, electronic, and chemical properties that they can contribute to the resulting conjugate. These may include quantum confined properties as typified by the size-tunable photoluminescence (PL) of nanocrystalline semiconductor quantum dots (QD), the plasmon resonances of gold NPs, the electrical properties of carbon allotrope NMs, and the paramagnetism and catalytic properties available to certain metal alloy and metal oxide NPs.

Algar W.R.,Center for Bio Molecular Science and Engineering | Algar W.R.,George Mason University | Algar W.R.,University of British Columbia | Ancona M.G.,Washington Technology | And 4 more authors.
ACS Nano | Year: 2012

Semiconductor nanocrystals, or quantum dots (QDs), are one of the most widely utilized nanomaterials for biological applications. Their cumulative physicochemical and optical properties are both unique among nanomaterials and highly advantageous. In particular, Förster resonance energy transfer (FRET) has been widely utilized as a spectroscopic tool with QDs, whether for characterizing QD bioconjugates as a "molecular ruler" or for modulating QD luminescence "on" and "off" in biosensing configurations. Here, we investigate the assembly and utility of a new "concentric" FRET relay that comprises a central QD conjugated with multiple copies of two different peptides, each labeled with one of two fluorescent dyes, Alexa Fluor 555 (A555) or Alexa Fluor 647 (A647). Energy transfer occurs from the QD to the A555 (FRET1) then to the A647 (FRET2) and, to a lesser extent, directly from the QD to the A647 (FRET3). We show that such an arrangement can provide insight into the interfacial distribution of peptides assembled to the QD and can further be utilized for sensing proteolytic activity. In the latter, progress curves for digestion of the assembled peptides by two prototypical proteases, trypsin and chymotrypsin, were measured from the relative QD, A555 and A647 PL contributions, and used to extract Michaelis-Menten kinetic parameters. We further show that the concentric FRET relay, as a single nanoparticle vector, can track the tryptic activation of a proenzyme, chymotrypsinogen, to active chymotrypsin. The concentric FRET relay is thus a potentially powerful tool for the characterization of QD bioconjugates and multiplexed sensing of coupled biological activity. © 2012 American Chemical Society.

Canedy C.L.,U.S. Navy | Abell J.,U.S. Navy | Merritt C.D.,U.S. Navy | Bewley W.W.,U.S. Navy | And 4 more authors.
Optics Express | Year: 2014

We report a narrow-ridge interband cascade laser emitting at λ ≈3.5 μm that produces up to 592 mW of cw power with a wallplug efficiency of 10.1% and beam quality factor of M2 = 3.7 at T = 25 °C. A pulsed cavity length study of broad-area lasers from the same wafer confirms that the 7-stage structure with thicker separate confinement layers has a reduced internal loss of ≈3 cm-1. More generally, devices from a large number of wafers with similar 7-stage designs and wavelengths spanning 2.95-4.7 μm exhibit consistently higher pulsed external differential quantum efficiencies than earlier state-of-the-art ICLs. © 2014 Optical Society of America.

Harmon S.R.,Sotera Defense Solutions | McKinney J.D.,U.S. Navy
Optics Express | Year: 2014

We introduce a novel technique for broadband RF disambiguation which exploits a known jitter imparted onto the sampling rate of an optical pulse source in a subsampled analog optical link. Coarse disambiguation to bandwidths equal to the sample rate is achieved using pure tones as example waveforms by comparing the amplitude of the jitterinduced sidebands relative to the measured signal within the fundamental Nyquist band (frep/2). This sampling technique allows for ultra-wideband signal recovery with a single measurement. In a first-of-its-kind photonics demonstration we show reliable disambiguation for signals with center frequencies spanning 1 MHz - 40 GHz. © 2014 Optical Society of America.

Matis B.R.,U.S. Navy | Bulat F.A.,Sotera Defense Solutions | Friedman A.L.,U.S. Navy | Houston B.H.,U.S. Navy | Baldwin J.W.,U.S. Navy
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A giant negative magnetoresistance of up to 28% at 2.5 T is observed in plasma hydrogenated graphene at the charge neutrality point without any sign of saturation at 2.0 K. A detailed analysis of the gate voltage dependence demonstrates a suppression of the giant negative magnetoresistance, which is accompanied by a crossover from strong localization at low carrier concentrations to weak localization at higher carrier concentrations. Evidence of asymmetry in the electron/hole transport is found in the magnetic field traces at low temperature. The asymmetrical transport is attributed to charge transfer processes at the graphene/metal interface and demonstrates the effect of using invasive contact geometries in hydrogenated graphene devices. © 2012 American Physical Society.

Blanco-Canosa J.B.,Scripps Research Institute | Blanco-Canosa J.B.,Barcelona Institute for Research in Biomedicine | Wu M.,University of British Columbia | Susumu K.,U.S. Navy | And 6 more authors.
Coordination Chemistry Reviews | Year: 2014

The utility of luminescent semiconductor quantum dots (QDs) in biological applications is directly dependent upon their ability to undergo bioconjugation to proteins, peptides, DNA, drugs and indeed all other manner of biomolecules. In this focused review, we provide an overview of the diverse chemistries that are used for these purposes, including a special emphasis on recent progress by our groups toward optimizing or developing new chemistries. We begin by examining the characteristics and activity ideally desired from QD-bioconjugates, along with the linkage chemistries that are most often utilized. The utility of polyhistidine-mediated metal-affinity coordination to QD surfaces or surface functionalizing ligands is then described in detail. This particular conjugation approach is highly desirable due to its functional simplicity and the control it can afford over the final QD-bioassembly. A variety of other modular, chemoselective ligation chemistries that can be applied either directly on the QD or to the biological to facilitate subsequent QD assembly are described, including aniline-catalyzed imine ligation, thiol-exchange, thiol-targeting iodoacetate chemistry, and Cu(I)-catalyzed azide-alkyne cycloaddition. Commercial QD labeling chemistries that incorporate some of these bioconjugation approaches are also highlighted. Due to their continued widespread use, bioconjugation routes that target the QD surface functionalizing and solubilizing ligands are covered, as are improvements in their functional implementation. Selected examples of applications that incorporate QD-bioconjugates assembled using the different chemistries described are included where appropriate, along with discussion of their benefits and liabilities within that application. Finally, a perspective on remaining issues and how this field will evolve is offered. © 2013 Published by Elsevier B.V.

Matis B.R.,U.S. Navy | Burgess J.S.,U.S. Navy | Bulat F.A.,Sotera Defense Solutions | Friedman A.L.,U.S. Navy | And 2 more authors.
ACS Nano | Year: 2012

Figure Persented: We report the first observation of the n-type nature of hydrogenated graphene on SiO 2 and demonstrate the conversion of the majority carrier type from electrons to holes using surface doping. Density functional calculations indicate that the carrier type reversal is directly related to the magnitude of the hydrogenated graphene's work function relative to the substrate, which decreases when adsorbates such as water are present. Additionally, we show by temperature-dependent electronic transport measurements that hydrogenating graphene induces a band gap and that in the moderate temperature regime [220-375 K], the band gap has a maximum value at the charge neutrality point, is tunable with an electric field effect, and is higher for higher hydrogen coverage. The ability to control the majority charge carrier in hydrogenated graphene, in addition to opening a band gap, suggests potential for chemically modified graphene p-n junctions. © 2011 American Chemical Society.

Carter S.G.,U.S. Navy | Sweeney T.M.,U.S. Navy | Kim M.,Sotera Defense Solutions | Kim C.S.,U.S. Navy | And 6 more authors.
Nature Photonics | Year: 2013

A key ingredient for a quantum network is an interface between stationary quantum bits and photons, which act as flying qubits for interactions and communication. Photonic crystal architectures are promising platforms for enhancing the coupling of light to solid-state qubits. Quantum dots can be integrated into a photonic crystal, with optical transitions coupling to photons and spin states forming a long-lived quantum memory. Many researchers have now succeeded in coupling these emitters to photonic crystal cavities, but there have been no demonstrations of a functional spin qubit and quantum gates in this environment. Here, we have developed a coupled cavity-quantum dot system in which the dot is controllably charged with a single electron. We perform the initialization, rotation and measurement of a single electron spin qubit using laser pulses, and find that the cavity can significantly improve these processes. © 2013 Macmillan Publishers Limited. All rights reserved.

McMorrow J.J.,Sotera Defense Solutions | Cress C.D.,Washington Technology | Affouda C.A.,Washington Technology
ACS Nano | Year: 2012

Figure Persented: We investigate charge injection into the gate dielectric of single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) having Al 2O 3 and HfO 2 gate dielectrics. We demonstrate the use of electric field gradient microscopy (EFM) to identify the sign and approximate the magnitude of the injected charge carriers. Charge injection rates and saturation levels are found to differ between electrons and holes and also vary according to gate dielectric material. Electrically, Al 2O 3 gated devices demonstrate smaller average hysteresis and notably higher average on-state current and p-type mobility than those gated by HfO 2. These differences in transfer characteristics are attributed to the charge injection, observed via EFM, and correlate well with differences in tunneling barrier height for electrons and holes formed in the conduction and valence at the SWCNT/dielectric interface, respectively. This work emphasizes the need to understand the SWCNT/dielectric interface to overcome charge injection that occurs in the focused field region adjacent to SWCNTs and indicates that large barrier heights are key to minimizing the effect. © 2012 American Chemical Society.

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