George C. Schatz

Northwestern University, Evanston, Illinois, United States

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Publications (887)4535.1 Total impact

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    ABSTRACT: Mixed silver and gold plasmonic nanoparticle architectures are synthesized using DNA-programmable assembly, unveiling exquisitely tunable optical properties that are predicted and explained both by effective thin-film models and explicit electrodynamic simulations. These data demonstrate that the manner and ratio with which multiple metallic components are arranged can greatly alter optical properties, including tunable color and asymmetric reflectivity behavior of relevance for thin-film applications.
    No preview · Article · Feb 2016 · Advanced Materials
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    ABSTRACT: Ultrafast surface-enhanced Raman spectroscopy (SERS) has the potential to study molecular dynamics near plasmonic surfaces to better understand plasmon-mediated chemical reactions such as plasmonically-enhanced photocatalytic or photovoltaic processes. This review discusses the combination of ultrafast Raman spectroscopic techniques with plasmonic substrates for high temporal resolution, high sensitivity, and high spatial resolution vibrational spectroscopy. First, we introduce background information relevant to ultrafast SERS: the mechanisms of surface enhancement in Raman scattering, the characterization of plasmonic materials with ultrafast techniques, and early complementary techniques to study molecule-plasmon interactions. We then discuss recent advances in surface-enhanced Raman spectroscopies with ultrafast pulses with a focus on the study of molecule-plasmon coupling and molecular dynamics with high sensitivity. We also highlight the challenges faced by this field by the potential damage caused by concentrated, highly energetic pulsed fields in plasmonic hotspots, and finally the potential for future ultrafast SERS studies.
    Full-text · Article · Feb 2016 · Chemical Society Reviews
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    ABSTRACT: Simplicity and low cost has positioned inkjet paper- and fabric-based 3D substrates as two of the most commonly used surface-enhanced Raman spectroscopy (SERS) platforms for the detection and the identification of chemical and biological analytes down to the nanogram and femtogram levels. The relationship between far-field and near-field properties of these 3D SERS platforms remains poorly understood and warrants more detailed characterization. Here, we investigate the extremely weak optical scattering observed from commercial and home-fabricated paper-, as well as fabric-based 3D SERS substrates. Using wavelength scanned surface-enhanced Raman excitation spectroscopy (WS-SERES) and finite-difference time-domain (FDTD) calculations we were able to determine their near-field SERS properties and correlate them with morphological and far-field properties. It was found that nanoparticle dimers, trimers, and higher order nanoparticle clusters primarily determine the near-field properties of these substrates. At the same time, the far-field response of 3D SERS substrates either originates primarily from the monomers or cannot be clearly defined. Using FDTD we demonstrate that LSPR bands of nanoparticle aggregates near perfectly overlap with the maxima of the near-field surface-enhanced Raman scattering responses of the 3D SERS substrates. This behavior of far-field spectroscopic properties and near-field surface-enhanced Raman scattering has not been previously observed for 2D SERS substrates, known as nanorod arrays. The combination of these analytical approaches provides a full spectroscopic characterization of 3D SERS substrates, while FDTD simulation can be used to design new 3D SERS substrates with tailored spectral characteristics.
    No preview · Article · Feb 2016 · The Analyst
  • Z. Yu · F. Tantakitti · T. Yu · L. C. Palmer · G. C. Schatz · S. I. Stupp
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    ABSTRACT: Covalent and supramolecular polymers are two distinct forms of soft matter, composed of long chains of covalently and noncovalently linked structural units, respectively. We report a hybrid system formed by simultaneous covalent and supramolecular polymerizations of monomers. The process yields cylindrical fibers of uniform diameter that contain covalent and supramolecular compartments, a morphology not observed when the two polymers are formed independently. The covalent polymer has a rigid aromatic imine backbone with helicoidal conformation, and its alkylated peptide side chains are structurally identical to the monomer molecules of supramolecular polymers. In the hybrid system, covalent chains grow to higher average molar mass relative to chains formed via the same polymerization in the absence of a supramolecular compartment. The supramolecular compartments can be reversibly removed and re-formed to reconstitute the hybrid structure, suggesting soft materials with novel delivery or repair functions.
    No preview · Article · Jan 2016 · Science
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    ABSTRACT: This work demonstrates for the first time the capability of measuring surface vibrational spectra for adsorbates during atomic layer deposition (ALD) reactions using operando surface-enhanced Raman spectroscopy (SERS). We use SERS to study alumina ALD growth at 55 °C on bare silver film-over nanosphere (AgFON) substrates as well as AgFONs functionalized with thiol self-assembled monolayers (SAMs). On bare AgFONs, we observe the growth of Al-C stretches, symmetric C-H and asymmetric C-H stretches during the trimethylaluminum (TMA) dose half-cycle and their subsequent decay after dosing H2O. Al-C and C-H vibrational modes decay in intensity with time even without H2O exposure providing evidence that residual H2O in the ALD chamber reacts with –CH3 groups on AgFONs. The observed Al-C stretches are attributed to TMA dimeric species on the AgFON surface in agreement with density functional theory (DFT) studies. We observe Al-C stretches and no thiol vibrational frequency shifts after dosing TMA on AgFONs functionalized with toluenethiol and benzenethiol SAMs. Conversely, we observe thiol vibrational frequency shifts and no Al-C stretches for AgFONs functionalized with 4-mercaptobenzoic acid and 4-mercaptophenol SAMs. Lack of observed Al-C stretches for COOH- and OH-terminated SAMs is explained by the spacing of Al-(CH3)x groups from the SERS substrate. TMA penetrates through SAMs and reacts directly with Ag for benzenethiol and toluenethiol SAMs and selectively reacts with the –COOH and –OH groups for 4-mercaptobenzoic acid and 4-mercaptophenol SAMs, respectively. The high sensitivity and chemical specificity of SERS provides valuable information about the location of ALD deposits with respect to the enhancing substrate. This information can be used to evaluate the efficacy of SAMs in blocking or allowing ALD deposition on metal surfaces. The ability to probe ALD reactions using SERS under realistic reaction conditions will lead to a better understanding of the mechanisms of ALD reactions.
    No preview · Article · Jan 2016 · The Journal of Physical Chemistry C
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    ABSTRACT: By means of two supramolecular systems-peptide amphiphiles engaged in hydrogen-bonded β-sheets, and chromophore amphiphiles driven to assemble by π-orbital overlaps-we show that the minima in the energy landscapes of supramolecular systems are defined by electrostatic repulsion and the ability of the dominant attractive forces to trap molecules in thermodynamically unfavourable configurations. These competing interactions can be selectively switched on and off, with the order of doing so determining the position of the final product in the energy landscape. Within the same energy landscape, the peptide-amphiphile system forms a thermodynamically favoured product characterized by long bundled fibres that promote biological cell adhesion and survival, and a metastable product characterized by short monodisperse fibres that interfere with adhesion and can lead to cell death. Our findings suggest that, in supramolecular systems, functions and energy landscapes are linked, superseding the more traditional connection between molecular design and function.
    Full-text · Article · Jan 2016 · Nature Materials
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    Full-text · Article · Jan 2016 · The Journal of Physical Chemistry B
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    ABSTRACT: The influence of molecular structure on excited state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt(ppy)(µ-R2pz)]2 where ppy = 2-phenylpyridine, pz = pyrazolate and R = H, Me, Ph, or tBu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt-Pt distance. At large Pt-Pt distances there is little interaction between the subunits and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt(II) centers are brought closer together with bulky bridging ligands, they interact through their orbitals and the S1 and T1 states are best characterized as metal metal to ligand charge transfer (MMLCT) in character. The results of the fs TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast timescales (S1 < 200 fs) while there are two relaxation processes occurring within the triplet manifold, 1 = 0.5 - 3.2 ps and 2 = 20 - 70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt-Pt distances further contract in the T1 3MMLCT states, therefore slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur.
    No preview · Article · Jan 2016 · The Journal of Physical Chemistry A
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    ABSTRACT: Beam pen lithography (BPL) in the liquid phase is evaluated. The effect of tip-substrate gap and aperture size on patterning performance is systematically investigated. As a proof-of-concept experiment, nanoarrays of nucleotides are synthesized using BPL in an organic medium, pointing toward the potential of using liquid phase BPL to perform localized photochemical reactions that require a liquid medium.
    Full-text · Article · Jan 2016 · Small
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    Full-text · Article · Jan 2016 · Journal of Physical Chemistry Letters
  • Michael B. Ross · Chad A. Mirkin · George C. Schatz

    No preview · Article · Dec 2015 · The Journal of Physical Chemistry C
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    Danqing Wang · Ankun Yang · Alexander J. Hryn · George C. Schatz · Teri W. Odom

    Full-text · Dataset · Nov 2015
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    Danqing Wang · Ankun Yang · Alexander J. Hryn · George C. Schatz · Teri W. Odom

    Full-text · Article · Nov 2015
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    ABSTRACT: Shape-controlled synthesis of gold nanoparticles generally involves the use of surfactants, typically cetyltrimethylammonium (CTAX, X = Cl(-) , Br(-) ), to regulate the nucleation growth process and to obtain colloidally stable nanoparticles. The surfactants adsorb on the nanoparticle surface making further functionalization difficult and therefore limit their use in many applications. Herein, the influence of CTAX on nanoparticle sensitivity to local dielectric environment changes is reported. It is shown, both experimentally and theoretically, that the CTAX bilayer significantly reduces the refractive index (RI) sensitivity of anisotropic gold nanoparticles such as nanocubes and concave nanocubes, nanorods, and nanoprisms. The RI sensitivity can be increased by up to 40% by removing the surfactant layer from nanoparticles immobilized on a solid substrate using oxygen plasma treatment. This increase compensates for the otherwise problematic decrease in RI sensitivity caused by the substrate effect. Moreover, the removal of the surfactants both facilitates nanoparticle biofunctionalization and significantly improves their catalytic properties. The strategy presented herein is a simple yet effective universal method for enhancing the RI sensitivity of CTAX-stabilized gold nanoparticles and increasing their potential as transducers in nanoplasmonic sensors, as well as in catalytic and biomedical applications.
    Full-text · Article · Nov 2015 · Small
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    Cheng-Tsung Eric Lai · Yu Zhang · George C Schatz
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    ABSTRACT: Work done by Bennett et al. (Nature 2002, 420, 398-401) demonstrated that Ca(2+) ions can be actively transported through a lipid bilayer membrane by an artificial photosynthetic machine. However, details of the pump process, such as the oxidation state of the shuttle molecule and stoichiometry of the shuttle-ion complex, are not fully understood, which hinders the development of ion pumps of this type with higher efficiency. In this study, we combine all atom molecular dynamics simulations and quantum mechanics calculations to estimate the timescale of the shuttle-ion complex diffusion process and charge transfer step. We find that the process of shuttle-ion complex diffusion across the lipid bilayer membrane is the rate-limiting step, with a timescale of seconds to minutes. Other processes, such as the timescale of charge transfer between the redox reaction center and the shuttle molecule have ps timescales. We also show that a shuttle-ion complex with 2:1 stoichiometry ratio has a lower energy barrier across the lipid membrane than other choices of complexes. The calculations show that the Ca(2+) ion is likely to be shuttled by a semiquinone type of shuttle molecule as this has the lowest free energy barrier across the lipid bilayer membrane, the fewest electrons transferred in the redox cycle, and it does not generate (or require) proton flow. Estimates of ion flow rates are consistent with measured values.
    Full-text · Article · Nov 2015 · The Journal of Physical Chemistry B
  • Sameer Patwardhan · George C. Schatz
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    ABSTRACT: For electrochemical device applications metal organic frameworks (MOFs) must exhibit suitable conduction properties. To this end, we have performed computational studies of intermolecular charge transfer in MOFs consisting of hexa-ZrIV nodes and tetratopic carboxylate linkers. This includes an examination of the electronic structure of linkers that are derived from tetraphenyl benzene 1, tetraphenyl pyrene 2, and tetraphenyl porphyrin 3 molecules. These results are used to determine charge transfer propensities in MOFs, within the framework of Marcus theory, including an analysis of the key parameters (charge transfer integral t, reorganization energy λ, and free energy change δG0) and evaluation of figures of merit for charge transfer based on the chemical structures of the linkers. This qualitative analysis indicates that delocalization of the HOMO/LUMO on terminal substituents increases t and decreases λ, while weaker binding to counterions decreases δG0, leading to better charge transfer propensity. Subsequently, we study hole transfer in the linker 2 containing MOFs, NU-901 and NU-1000, in detail and describe mechanisms (hopping and superexchange) that may be operative under different electrochemical conditions. Comparisons with experiment are provided where available. On the basis of the redox and catalytic activity of nodes and linkers, we propose three possible schemes for constructing electrochemical devices for catalysis. We believe that the results of this study will lay the foundation for future experimental work on this topic.
    No preview · Article · Oct 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Chemical bonds are a key determinant of the structure and properties of a material. Thus, rationally designing arbitrary materials requires complete control over the bond. While atomic bonding is dictated by the identity of the atoms, nanoparticle superlattice engineering, where nanoparticle "atoms" are held together by DNA "bonds", offers a route to design crystal lattices in a way that nature cannot: through altering the oligonucleotide bond. Herein, the use of RNA, as opposed to DNA, is explored by synthesizing superlattices in which nanoparticles are bonded by DNA/DNA, RNA/RNA, and DNA/RNA duplexes. By moving beyond nanoparticle superlattices assembled only with DNA, a new degree of freedom is introduced, providing programmed responsiveness to enzymes and greater bond versatility. Therefore, the oligonucleotide bond can have programmable function beyond dictating the structure of the material and moves nanoparticle superlattices closer to naturally occurring biomaterials, where the line between structural and functional elements is blurred.
    No preview · Article · Oct 2015 · Journal of the American Chemical Society
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    ABSTRACT: Two complementary small molecule-DNA hybrid (SMDH) building blocks have been combined to form well-defined supramolecular cage dimers at DNA concentrations as high as 102 μM, made possible by combining a flexible small-molecule core and three DNA arms of moderate lengths (<20 base pairs). These results were successfully modeled by coarse-grained molecular dynamics (CGMD) simulations, which also reveal that the formation of ill-defined networks in the case of longer DNA arms can be significantly biased by the presence of deep kinetic traps. Notably, melting point studies revealed that cooperative melting behavior can be used as a means to distinguish the relative propensities for dimer vs network formation from complimentary fSMDH3 components: sharp, enhanced melting transitions were observed for assemblies that result mostly in cage dimers while no cooperative melting behavior was observed for assemblies that form ill-defined networks.
    Full-text · Article · Sep 2015 · Journal of the American Chemical Society
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    ABSTRACT: Myotonic Dystrophy 1 (DM1) is a genetic disease caused by expansion of CTG repeats in DNA. Once transcribed, these repeats form RNA hairpins with repeating 1×1 nucleotide UU internal loop motifs, r(CUG)n, which attract muscleblind-like 1 (MBNL1) protein leading to the disease. In DM1 CUG can be repeated thousands of times, so these structures are intractable to characterization using structural biology. However, inhibition of MBNL1-r(CUG)n binding requires a detailed analysis of the 1×1 UU internal loops. In this contribution we employ regular and umbrella sampling molecular dynamics (MD) simulations to describe the structural and thermodynamic properties of 1×1 UU internal loops. Calculations were run on a reported crystal structure and a designed system, which mimics an infinitely long RNA molecule with continuous CUG repeats. Two-dimensional (2D) potential of mean force (PMF) surfaces were created by umbrella sampling, and the discrete path sampling (DPS) method was utilized to investigate the energy landscape of 1×1 UU RNA internal loops, revealing that 1×1 UU base pairs are dynamic and strongly prefer the anti–anti conformation. Two 2D PMF surfaces were calculated for the 1×1 UU base pairs, revealing several local minima and three syn–anti ↔ anti–anti transformation pathways. Although at room temperature the syn–anti ↔ anti–anti transformation is not observed on the MD time scale, one of these pathways dominates the dynamics of the 1×1 UU base pairs in temperature jump MD simulations. This mechanism has now been treated successfully using the DPS approach. Our results suggest that local minima predicted by umbrella sampling calculations could be stabilized by small molecules, which is of great interest for future drug design. Furthermore, distorted GC/CG conformations may be important in understanding how MBNL1 binds to RNA CUG repeats. Hence we provide new insight into the dynamic roles of RNA loops and their contributions to presently incurable diseases.
    Full-text · Article · Aug 2015 · Journal of Chemical Theory and Computation
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    Biswajit Saha · Al'ona Furmanchuk · Yuris Dzenis · George C. Schatz

    Full-text · Dataset · Aug 2015

Publication Stats

51k Citations
4,535.10 Total Impact Points

Institutions

  • 1977-2016
    • Northwestern University
      • • Department of Chemistry
      • • Department of Mechanical Engineering
      Evanston, Illinois, United States
    • Massachusetts Institute of Technology
      • Department of Chemistry
      Cambridge, MA, United States
  • 2013-2015
    • University of Notre Dame
      South Bend, Indiana, United States
  • 2011
    • The University of Manchester
      • School of Chemistry
      Manchester, England, United Kingdom
  • 1992-2008
    • Northwest University
      Evanston, Illinois, United States
  • 2007
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
    • Universität Konstanz
      Constance, Baden-Württemberg, Germany
  • 2004
    • Hungarian Academy of Sciences
      Budapeŝto, Budapest, Hungary
  • 2000
    • Academia Sinica
      T’ai-pei, Taipei, Taiwan
  • 1998
    • Hebrew University of Jerusalem
      Yerushalayim, Jerusalem, Israel
  • 1971-1997
    • Argonne National Laboratory
      • Center for Nanoscale Materials
      Lemont, Illinois, United States
  • 1989
    • University of Colorado at Boulder
      • Department of Chemistry and Biochemistry
      Boulder, Colorado, United States
  • 1983
    • Stanford University
      • Department of Chemistry
      Palo Alto, California, United States
  • 1973-1980
    • California Institute of Technology
      • Arthur Amos Noyes Laboratory of Chemical Physics
      Pasadena, California, United States
  • 1974
    • Soreq Nuclear Research Center
      Yerushalayim, Jerusalem, Israel