Columbia, MO, United States
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Bhatnagar K.,University of Missouri | Pathak A.,University of Missouri | Menke D.,University of Missouri | Cornish P.V.,University of Missouri | And 4 more authors.
Nanotechnology | Year: 2012

We demonstrate strong electromagnetic field enhancement from nano-gaps embedded in silver gratings for visible wavelengths. These structures fabricated using a store-bought HD-DVD worth $10 and conventional micro-contact printing techniques have shown maximum fluorescence enhancement factors of up to 118 times when compared to a glass substrate under epi-fluorescent conditions. The novel fabrication procedure provides for the development of a cost-effective and facile plasmonic substrate for low-level chemical and biological detection. Electromagnetic field simulations were also performed that reveal the strong field confinement in the nano-gap region embedded in the silver grating, which is attributed to the combined effect of localized as well as propagating surface plasmons. © 2012 IOP Publishing Ltd.


Bok S.,Nanos Technologies LLC | Korampally V.,University of Missouri | Polo-Parada L.,University of Missouri | Folk W.,University of Missouri | And 4 more authors.
Proceedings of IEEE Sensors | Year: 2010

In this paper, a simple and robust sensing assay platform for detection of biological materials is reported. The fluorescence based sensing platform benefits from the combined use of our novel dye-doped nanoparticle tags and nanoporous high surface area (∼1,400 m2/g) films to achieve high intrinsic signal amplification. The dye-doped nanoparticles are synthesized from poly-methylsilsesquioxane (PMSSQ) encapsulating fluorescent dye molecules that can be conjugated to antibodies and proteins. We have achieved conjugation of up to 64 dye molecules per single antibody, which represents more than an order of magnitude increase in conjugation efficiency compared to conjugation of free dye molecules. Capture of the dye-doped nanoparticle labeled antibodies by nanoporous organosilicate (NPO) films has yielded 540 fold increase in fluorescence response compared to immobilization of dye labeled antibodies on (flat) glass substrates. This assay demonstrates a general way for detection of analytes in very low concentration. ©2010 IEEE.


Mukherjee S.,University of Missouri | Ramalingam B.,University of Missouri | Gangopadhyay K.,University of Missouri | Gangopadhyay K.,Nanos Technologies LLC | Gangopadhyay S.,University of Missouri
Journal of the Electrochemical Society | Year: 2014

Electrochemical stability of Pt nanoparticles in acidic environments is a pressing issue in the field of catalysis. Pt nanoparticles immobilized on a support tend to undergo the phenomena of dissolution and coarsening leading to loss in effective surface area which undermines the long-term applicability of these supported nanoparticles. Sub-2 nm Pt nanoparticles with controllable size distribution and surface number densities were deposited using tilted target sputtering (TTS). Electron beam-induced coarsening and potentiodynamic cycling in acidic solutions was utilized to study the size-dependent and support-dependent stability of these Pt nanoparticles. Direct evidence of a correlation between Pt nanoparticle coarsening on supporting surfaces and their different surface energies was observed under prolonged E-beam exposure through HRTEM imaging. Utilizing potentiodynamic cycling, it was also observed that crystalline particles above a mean size of 1.5 nm diameter show exceptional stability regardless of supporting surface, meanwhile, sub-nm Pt nanoparticles on few layer graphene (FLG) support show better stability properties compared to those deposited on fluorine-doped tin oxide (FTO) support. © 2014 The Electrochemical Society. All rights reserved.


Zheng H.,University of Missouri | Mukherjee S.,University of Missouri | Gangopadhyay K.,University of Missouri | Gangopadhyay K.,Nanos Technologies LLC | Gangopadhyay S.,University of Missouri
Journal of Materials Science: Materials in Electronics | Year: 2015

The doping/strain induced by ultrafine sputtered Pt nanoparticles (NPs) of different sizes on single layer graphene is studied through conduction channel modification of graphene-based field-effect transistors and subsequent Raman characterization. For sub-nm (0.5 nm) sized Pt NPs, a substantial Dirac point shift is observed in the I–V characteristics, suggestive of n-type doping of the large area single layer graphene through the process of charge transfer and chemical interaction. Conversely, for larger (1.1 nm) Pt NPs, minimal Dirac point shift is observed, indicating lack of the charge transfer induced doping effect. The representative Raman signatures corroborate with the electrical characterization results and indicate while charge transfer dominates Raman peak shift for the 0.5 nm Pt NP decorated graphene, strain effect dominates in case of the larger 1.1 nm Pt NP. © 2015, Springer Science+Business Media New York.


Zheng H.,University of Missouri | Ramalingam B.,University of Missouri | Mukherjee S.,University of Missouri | Zhou Y.,University of Missouri | And 5 more authors.
Sensing and Bio-Sensing Research | Year: 2016

We report a direct conversion solid-state neutron detection device fabricated by combining the large neutron capture cross-section of 10B with the charge trapping attributes of sub-2 nm Pt nanoparticles (Pt NPs) in MOSCAP structures. The 10B embedded polystyrene based neutron conversion layer also serves as the dielectric layer. Neutron sensing is achieved through carrier generation within the active 10B based dielectric layer and subsequent transfer to the embedded Pt NP layers, resulting in a significant change of the device's flat-band voltage upon ex-situ characterization. Both single and dual Pt NP layer embedded architectures, with varying electron addition energies, were tested within this study. While dual-layer Pt NPs embedded direct conversion devices with higher electron addition energy are shown to successfully capture charges generated through energetic reaction product upon neutron capture, the single Pt NP layer embedded device structure with lower electron addition energy displays signs of charge loss attributable to direct tunneling in the ex-situ capacitance-voltage measurement. Although only ex-situ detector operation is demonstrated within the realms of this study, sensitive in-situ neutron detectors and ultra-stable ex-situ dosimeters may be achievable utilizing a similar structure by fine-tuning the Pt NP size and the number of Pt NP layers in the device. © 2016 The Authors.


Kargupta R.,University of Missouri | Bok S.,University of Missouri | Darr C.M.,University of Missouri | Crist B.D.,University of Missouri | And 4 more authors.
Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology | Year: 2014

Bacterial colonization and biofilm formation on an orthopedic implant surface is one of the worst possible outcomes of orthopedic intervention in terms of both patient prognosis and healthcare costs. Making the problem even more vexing is the fact that infections are often caused by events beyond the control of the operating surgeon and may manifest weeks to months after the initial surgery. Herein, we review the costs and consequences of implant infection as well as the methods of prevention and management. In particular, we focus on coatings and other forms of implant surface modification in a manner that imparts some antimicrobial benefit to the implant device. Such coatings can be classified generally based on their mode of action: surface adhesion prevention, bactericidal, antimicrobial-eluting, osseointegration promotion, and combinations of the above. Despite several advances in the efficacy of these antimicrobial methods, a remaining major challenge is ensuring retention of the antimicrobial activity over a period of months to years postoperation, an issue that has so far been inadequately addressed. Finally, we provide an overview of additional figures of merit that will determine whether a given antimicrobial surface modification warrants adoption for clinical use. For further resources related to this article, please visit the WIREs website. Conflict of interest: The authors have declared no conflicts of interest for this article. © 2014 Wiley Periodicals, Inc.


Hamm S.C.,University of Missouri | Shankaran R.,University of Missouri | Korampally V.,University of Missouri | Bok S.,University of Missouri | And 7 more authors.
ACS Applied Materials and Interfaces | Year: 2012

We present a new approach for fabricating robust, regenerable antimicrobial coatings containing an ionic liquid (IL) phase incorporating silver nanoparticles (AgNPs) as a reservoir for Ag 0/Ag + species within sol-gel-derived nanocomposite films integrating organosilicate nanoparticles. The IL serves as an ultralow volatility (vacuum-compatible) liquid target, allowing for the direct deposition and dispersion of a high-density AgNP "ionosol" following conventional sputtering techniques. Two like-anion ILs were investigated in this work: methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N 8881] [Tf 2N], and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [emim][Tf 2N]. Silver ionosols derived from these two ILs were incorporated into silica-based sol-gel films and the resultant antimicrobial activity evaluated against Pseudomonas aeruginosa bacteria. Imaging of the surface morphologies of the as-prepared films established a link between an open macroporous film architecture and the observation of high activity. Nanocomposites based on [N 8881][Tf 2N] displayed excellent antimicrobial activity against P. aeruginosa over multiple cycles, reducing cell viability by 6 log units within 4 h of contact. Surprisingly, similar films prepared from [emim][Tf 2N] presented negligible antimicrobial activity, an observation we attribute to the differing abilities of these IL cations to infiltrate the cell wall, regulating the influx of silver ions to the bacterium's interior. © 2012 American Chemical Society.


Bok S.,University of Missouri | Korampally V.,University of Missouri | Polo-Parada L.,University of Missouri | Mamidi V.,University of Missouri | And 6 more authors.
Nanotechnology | Year: 2012

We report ultrabright, photostable, sub-25nm nanoparticle agglomerates (suprananoparticles) assembled from a few hundred 3.3±0.9nm units, each hosting on average a single rhodamine 6G (Rh6G) dye molecule encased in a thin organosilicate cage. These individual Rh6G-doped nanoparticle (DOSNP) units consist of a hydrophobic core containing the dye and an ultrathin, conformal silicate shell modified by CO 2 plasma to confer a beneficial cage effect as well as surface hydrophilicity. The isolation of the dye within individual DOSNP units in the final 22±5nm agglomerate avoids dimerization and related spontaneous molecular interactions that otherwise lead to self-quenching in closely co-localized fluorophores. The resulting suprananoparticles are over 200 times brighter than the free Rh6G molecules in the same volume. There is no observable dye leaching, and the labels are 20-fold more resistant to photobleaching than free Rh6G in solution. We demonstrate the attractive features of DOSNPs as labels in bioimaging applications. © 2012 IOP Publishing Ltd.


Zheng H.,University of Missouri | Asbahi M.,Institute of Materials Research and Engineering of Singapore | Mukherjee S.,University of Missouri | Mathai C.J.,University of Missouri | And 5 more authors.
Nanotechnology | Year: 2015

Single-electron transistors incorporating single ∼1 nm gold nanocluster (AuNCs) and pentacene as a complex charge transport system have been used to study the quantum Coulomb blockade and its single electron tunnelling behaviour at room temperature (RT) (300 K). Monodisperse ultra-small (0.86 ± 0.30 nm) AuNCs were deposited by the tilted-target sputtering technique into 12 nm nanogaps fabricated by high-resolution e-beam lithography. Tunnelling resistance was modulated to ∼109 Ω by addition of a pentacene layer, allowing clear observation of quantum staircases and Coulomb oscillations with on/off current modulation ratio of ∼100 in RT current-voltage measurements. The electron addition energy and average quantized energy level spacing were found to be 282 and 80.4 meV, respectively, which are significantly larger than the thermal energy at 300 K (25.9 meV). © 2015 IOP Publishing Ltd.


Ramalingam B.,University of Missouri | Mukherjee S.,University of Missouri | Mathai C.J.,University of Missouri | Gangopadhyay K.,University of Missouri | And 2 more authors.
Nanotechnology | Year: 2013

This paper describes a tilted-target RF magnetron sputter deposition system to grow nanoparticles in a controlled way. With detailed characterization of ultra-high density (up to 1.1 × 1013 cm-2) and ultra-small size Pt nanoparticles (0.5-2 nm), it explains their growth and crystalline properties on amorphous Al2O3 thin films. It is shown that Pt nanoparticle size and number density can be precisely engineered by varying selected experimental parameters such as target angle, sputtering power and time of deposition to control the energy of the metal atoms in the deposition flux. Based on rate equation modelling of nanoparticle growth, three distinct growth regimes, namely nucleation dependent, coalescence dependent and agglomeration dependent regimes, were observed. The correlation between different nanoparticle growth regimes and the consequent crystal structure transformation, non-crystalline clusters → single crystalline nanoparticles → polycrystalline islands, is also discussed. © 2013 IOP Publishing Ltd.

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