@article {1573, title = {Electronic and Vibrational Dynamics of Hollow Au Nanocages Embedded in Cu2O Shells}, journal = {Photochemistry and Photobiology}, volume = {91}, year = {2015}, pages = {599{\textendash}606}, issn = {1751-1097}, doi = {10.1111/php.12432}, url = {http://dx.doi.org/10.1111/php.12432}, author = {Szymanski, Paul and Mahmoud, Mahmoud A. and O{\textquoteright}Neil, Daniel and Garlyyev, Batyr and El-Sayed, Mostafa A.} } @article {1575, title = {Light-responsive plasmonic arrays consisting of silver nanocubes and a photoisomerizable matrix.}, journal = {ACS Appl Mater Interfaces}, volume = {7}, year = {2015}, month = {2015 Mar 4}, pages = {4902-12}, abstract = {We report on the synthesis of novel branched organic-inorganic azo-polyhedral oligomeric silsesquioxane (POSS) conjugates (Azo-POSS) and their use as a stable active medium to induce reversible plasmonic modulations of embedded metal nanostructures. A dense monolayer of silver nanocubes was deposited on a quartz substrate using the Langmuir-Blodgett technique and subsequently coated with an ultrathin Azo-POSS layer. The reversible light-induced photoisomerization between the trans and cis states of the azobenzene-terminated branched POSS material results in significant changes in the refractive index (up to 0.17) at a wavelength of 380 nm. We observed that the pronounced and reversible change in the surrounding refractive index results in a corresponding hypsochromic plasmonic shift of 6 nm in the plasmonic band of the embedded silver nanocubes. The reversible tuning of the plasmonic modes of noble-metal nanostructures using a variable-refractive-index medium opens up the possibility of fabricating photoactive, hybrid, ultrathin coatings with robust, real-time, photoinitiated responses for prospective applications in photoactive materials that can be reversibly tuned by light illumination.}, issn = {1944-8252}, doi = {10.1021/am508993z}, author = {Ledin, Petr A and Russell, Michael and Geldmeier, Jeffrey A and Tkachenko, Ihor M and Mahmoud, Mahmoud A. and Shevchenko, Valery and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.} } @article {1578, title = {Wavelength-Selective Photocatalysis Using Gold{\textendash}Platinum Nanorattles}, journal = {The Journal of Physical Chemistry C}, volume = {119}, year = {2015}, pages = {18618-18626}, doi = {10.1021/acs.jpcc.5b05967}, url = {http://dx.doi.org/10.1021/acs.jpcc.5b05967}, author = {Mahmoud, Mahmoud A. and Garlyyev, Batyr and El-Sayed, Mostafa A.} } @article {1363, title = {Electrically Tunable Plasmonic Behavior of Nanocube-Polymer Nanomaterials Induced by a Redox Active Electrochromic Polymer}, journal = {ACS nano}, year = {2014}, isbn = {1936-0851}, author = {K{\"o}nig, Tobias AF and Ledin, Petr A and Kerszulis, Justin and Mahmoud, Mahmoud A. and El-Sayed, Mostafa A. and Reynolds, John R and Tsukruk, Vladimir V.} } @article {1399, title = {Aptamer-Assisted Assembly of Gold Nanoframe Dimers}, journal = {Particle \& Particle Systems Characterization}, volume = {30}, number = {12}, year = {2013}, pages = {1071-1078}, isbn = {1521-4117}, author = {Combs, Zachary A. and Malak, Sidney T. and K{\"o}nig, Tobias and Mahmoud, Mahmoud A. and Ch{\'a}vez, Jorge L and El-Sayed, Mostafa A and Kelley-Loughnane, Nancy and Tsukruk, Vladimir V.} } @article {1349, title = {Assemblies of silver nanocubes for highly sensitive SERS chemical vapor detection}, journal = {J. Mater. Chem. A}, volume = {1}, number = {8}, year = {2013}, note = {CAPLUS AN 2013:172950(Journal; Online Computer File)}, month = {//}, pages = {2777-2788}, publisher = {Royal Society of Chemistry}, type = {10.1039/c2ta00867j}, abstract = {Probably Ag nanocube (AgNC) aggregates within cylindrical pores (PAM-AgNC) can be employed as efficient nanostructures for highly efficient, robust, tunable, and reusable surface-enhanced Raman scattering (SERS) substrates for trace level org. vapor detection which is a challenging task in chem. detection. The authors demonstrate the ability to tune both the detection limit and the onset of signal satn. of the substrate by switching the adsorption behavior of AgNCs between highly aggregated and more disperse by varying the no. of adsorption-mediating polyelectrolyte bilayers on the pore walls of the membrane. The different AgNC distributions show large differences in the trace vapor detection limit of the common Raman marker benzenethiol (BT) and a widely used explosive binder N-Me-4-nitroaniline (MNA), demonstrating the importance of the large electromagnetic field enhancement assocd. with AgNC coupling. The SERS substrate with highly aggregated AgNCs within the cylindrical pores allows for consistent trace detection of mid ppb (\~{}500) for BT analyte, and a record limit of detection of low ppb (\~{}3) for MNA vapors with an estd. achievable limit of detection of \~{}600 ppt. The dispersed AgNC aggregates do not sat. at higher ppb concns., providing an avenue to distinguish between higher ppb concns. and increase the effective range of the SERS substrate design. A comparison between the AgNC substrate and an electroless deposition substrate with Ag quasi-nanospheres (PAM-AgNS) also demonstrates a higher SERS activity, and better detection limit, by the nanocube aggregates. This is supported by FDTD electromagnetic simulations that suggest that the higher integrated electromagnetic field intensity of the hot spots and the large specific interfacial areas impart greatly improved SERS for the AgNCs. Also, the AgNC substrate can be reused multiple times without significant loss of SERS activity which opens up new avenues for in-field monitoring. [on SciFinder(R)]}, keywords = {polymer electrolyte film silver nanocube nanosphere SERS sensor explosive, porous alumina silver nanoparticle SERS substrate explosive, silver nanocube nanosphere SERS sensor benzenethiol methyl nitroaniline polyelectrolyte, vapor sensor silver nanoparticle SERS substrate}, isbn = {2050-7496}, doi = {10.1039/c2ta00867j}, author = {Kodiyath, Rajesh and Malak, Sidney T. and Combs, Zachary A. and Koenig, Tobias and Mahmoud, Mahmoud A. and El-Sayed, Mostafa A. and Tsukruk, Vladimir V.} } @article {1350, title = {Enhancing Colloidal Metallic Nanocatalysis: Sharp Edges and Corners for Solid Nanoparticles and Cage Effect for Hollow Ones}, journal = {Acc Chem Res}, year = {2013}, note = {MEDLINE AN 2013361444(Journal; Article; (JOURNAL ARTICLE))}, month = {//}, abstract = {There are two main classes of metallic nanoparticles: solid and hollow. Each type can be synthesized in different shapes and structures. Practical use of these nanoparticles depends on the properties they acquire on the nanoscale. Plasmonic nanoparticles of silver and gold are the most studied, with applications in the fields of sensing, medicine, photonics, and catalysis. In this Account, we review our group{\textquoteright}s work to understand the catalytic properties of metallic nanoparticles of different shapes. Our group was the first to synthesize colloidal metallic nanoparticles of different shapes and compare their catalytic activity in solution. We found that the most active among these were metallic nanoparticles having sharp edges, sharp corners, or rough surfaces. Thus, tetrahedral platinum nanoparticles are more active than spheres. We proposed this happens because sharper, rougher particles have more valency-unsatisfied surface atoms (i.e., atoms that do not have the complete number of bonds that they can chemically accommodate) to act as active sites than smoother nanoparticles. We have not yet resolved whether these catalytically active atoms act as catalytic centers on the surface of the nanoparticle (i.e., heterogeneous catalysis) or are dissolved by the solvent and perform the catalysis in solution (i.e., homogenous catalysis). The answer is probably that it depends on the system studied. In the past few years, the galvanic replacement technique has allowed synthesis of hollow metallic nanoparticles, often called nanocages, including some with nested shells. Nanocage catalysts show strong catalytic activity. We describe several catalytic experiments that suggest the reactions occurred within the cage of the hollow nanocatalysts: (1) We synthesized two types of hollow nanocages with double shells, one with platinum around palladium and the other with palladium around platinum, and two single-shelled nanocages, one made of pure platinum and the other made of pure palladium. The kinetic parameters of each double-shelled catalyst were comparable to those of the single-shelled nanocage of the same metal as the inside shell, which suggests the reactions are taking place inside the cavity. (2) In the second set of experiments, we used double-shelled, hollow nanoparticles with a plasmonic outer gold surface and a non-plasmonic inner catalytic layer of platinum as catalysts. As the reaction proceeded and the dielectric function of the interior gold cavity changed, the plasmonic band of the interior gold shell shifted. This strongly suggested that the reaction had taken place in the nanocage. (3) Finally, we placed a catalyst on the inside walls of hollow nanocages and monitored the corresponding reaction over time. The reaction rate depended on the size and number of holes in the walls of the nanoparticles, strongly suggesting the confinement effect of a nanoreactor.[on SciFinder (R)]}, isbn = {1520-4898}, author = {Mahmoud, Mahmoud A. and Narayanan, Radha and El-Sayed, Mostafa A.} } @article {1386, title = {Hollow and Solid Metallic Nanoparticles in Sensing and in Nanocatalysis}, journal = {Chemistry of Materials}, volume = {26}, number = {1}, year = {2013}, pages = {44-58}, isbn = {0897-4756}, author = {Mahmoud, Mahmoud A. and O{\textquoteright}Neil, Daniel and El-Sayed, Mostafa A.} }