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Dive into the research topics where Francis P. Zamborini is active.

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Featured researches published by Francis P. Zamborini.


Journal of the American Chemical Society | 2010

Size-dependent electrochemical oxidation of silver nanoparticles.

Olga S. Ivanova; Francis P. Zamborini

Here we quantify the electrochemical oxidation of Ag nanoparticles (NPs) as a function of size by electrostatically attaching Ag NPs synthesized by seed-mediated growth in the presence of citrate (diameter = 8 to 50 nm) to amine-functionalized indium-tin oxide coated glass electrodes (Glass/ITO), obtaining a linear sweep voltammogram from 0.1 V, where Ag(0) is stable, up to 1.0 V, and observing the peak potential (E(p)) for oxidation of Ag(0) to Ag(+). Electrostatic attachment to the organic linker presumably removes direct interactions between Ag and ITO and allows control over the total Ag coverage by altering the soaking time. This is important as both metal-electrode interactions and overall Ag coverage can affect E(p). E(p) shifts positive from an average of 275 to 382 mV as the Ag NP diameter increases for a constant Ag coverage and under conditions of planar diffusion, suggesting a shift in E(p) due to a thermodynamic shift in E(0) for the Ag/Ag(+) redox couple with size. The negative shift in E(p) with decreasing Ag NP radius follows the general trend predicted by theory and agrees with previous qualitative experimental observations. A better understanding of metal nanostructure oxidation is crucial considering their potential use in many different applications and the importance of metal corrosion processes at the nanoscale.


Journal of the American Chemical Society | 2011

Hydrogen reactivity of palladium nanoparticles coated with mixed monolayers of alkyl thiols and alkyl amines for sensing and catalysis applications.

Monica Moreno; Francisco J. Ibañez; Jacek B. Jasinski; Francis P. Zamborini

Palladium monolayer-protected clusters (MPCs) coated with octylamines (C8NH(2)), hexanethiolates (C6S), and mixed monolayers of C8NH(2) and C6S exhibit significantly different reactivities with hydrogen gas, depending on the relative amounts of the two ligands coating the Pd nanoparticle surface, as determined by UV-vis spectroscopy of Pd MPCs in solution and electronic measurements of films of Pd MPCs as a function of exposure time to hydrogen. The average estimated composition of the ~3.0 nm diameter Pd MPCs was Pd(919)(C6S)(192) or Pd(919)(C8NH(2))(177-x)(C6S)(x), where x was varied to be 0, 3, 10, 16, 32, or 81 by the synthesis of pure C8NH(2) Pd MPCs and subsequent liquid-phase place exchange with a varied amount of C6SH. When x = 0-10, the Pd MPCs react strongly with H(2), leading to aggregated particles in solution and large irreversible changes in the morphology of films accompanied by an increase in film conductivity by 2-5 orders of magnitude. Pd(919)(C6S)(192) MPCs are stable against significant aggregation in solution and do not exhibit large film morphology changes, but they are also not highly reactive to H(2), as determined by minimal changes in the optical properties of solutions and the small, irreversible changes in the conductivity of films in the presence of H(2). Finally, when x is 32 and 81, the Pd MPCs are fairly stable, exhibit minimal aggregation or morphology changes, and readily react with H(2) based on the significant, reversible changes in film conductivity in the presence of H(2). Pd MPCs with mixed monolayers have the benefit of high H(2) reactivity while maintaining the structural stability necessary for sensing and catalysis applications.


Small | 2012

Chemiresistive Sensing with Chemically Modified Metal and Alloy Nanoparticles

Francisco J. Ibañez; Francis P. Zamborini

This review describes the use of chemically modified pure and alloyed metal nanoparticles for chemiresistive sensing applications. Chemically modified metal nanoparticles consist of a pure or alloyed metallic core with some type of chemical coating. Researchers have studied the electronic properties of 1D, 2D, and 3D assemblies of chemically modified metal nanoparticles, and even single individual nanoparticles. The interaction with the analyte alters the conductivity of the sensitive material, providing a signal to measure the analyte concentration. This review focuses on chemiresistive sensing of a wide variety of gas- and liquid-phase analytes with metal nanoparticles coated with organothiols, ions, polymers, surfactants, and biomolecules. Different strategies used to incorporate chemically modified nanoparticles into chemiresistive sensing devices are reviewed, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, and analytes (vapors, gases, liquids, biological materials), along with other important factors.


Journal of the American Chemical Society | 2009

Selective Attachment of Antibodies to the Edges of Gold Nanostructures for Enhanced Localized Surface Plasmon Resonance Biosensing

Srinivas R. Beeram; Francis P. Zamborini

Here we demonstrate control over the location of anti-immunoglobulin G (anti-IgG) proteins bound to Au nanoplates formed on glass and silicon samples. Preferential attachment to edge and vertex sites occurs by performing a thiol place-exchange reaction between mercaptoethanol (ME) attached to the Au nanostructures and mercaptoundecanoic acid (MUA) in solution, which localizes the carboxylic acid groups of MUA on the edge sites for subsequent amide linkage to anti-IgG. In contrast, anti-IgG attaches randomly onto the terrace regions of Au nanostructures functionalized directly in pure MUA or 1:10 MUA/ME solutions. Importantly, Au nanostructures with anti-IgG selectively bound to the edge sites exhibit significantly larger changes in the absorbance and wavelength of maximum absorbance (lambda(max)) of their localized surface plasmon resonance (LSPR) response upon binding than those with anti-IgG randomly attached to terrace regions. This leads to at least 500 times more sensitive detection of IgG down to 0.1 ng/mL.


ACS Nano | 2008

Chemiresistive sensing of volatile organic compounds with films of surfactant-stabilized gold and gold-silver alloy nanoparticles.

Francisco J. Ibañez; Francis P. Zamborini

Here we describe the chemiresistive sensing of volatile organic compounds (VOCs) with films of chemically synthesized approximately 4 nm diameter Au and AuAg alloy nanoparticles (NPs) stabilized by a surfactant, tetraoctylammonium bromide (TOABr). The chemiresistive sensing properties were measured over a concentration range of 100 to 0.04% saturation for methanol (MeOH), ethanol (EtOH), 2-propanol (IPA), and toluene (Tol) vapor analytes and compared directly to the chemiresistive sensing properties of films of 1.6 nm diameter hexanethiolate (C6S)-coated Au monolayer-protected clusters (MPCs). Films of TOABr-stabilized Au NPs exhibit the opposite response compared to those of C6S-coated Au MPCs. The details are unclear, but the mechanism likely involves changes in capacitive charging in the film or improved conductive pathways through the Au NPs upon incorporation of VOCs into the film for the former as opposed to the well-known change in electron hopping conductivity for the latter. This leads to a decrease in resistance in the presence of VOCs for TOABr Au as opposed to an increase for C6S Au. The TOABr Au sensors are more sensitive, especially for polar analytes, and have greater long-term stability compared to C6S Au. The limit of detection (LOD) for films of TOABr-coated Au NPs is 3, 2, 12, and 37 ppm for IPA, MeOH, EtOH, and Tol, respectively, as compared to 106, 326, 242, and 48 for C6S Au. Films of TOABr-stabilized AuAg alloy NPs exhibit the same type of response, but the sensitivity decreases dramatically with increasing Ag content, showing that the metal composition of the NPs in the film plays a role in the sensing properties, which has not been well-recognized in the literature.


ACS Nano | 2010

Purification of Gold Nanoplates Grown Directly on Surfaces for Enhanced Localized Surface Plasmon Resonance Biosensing

Srinivas R. Beeram; Francis P. Zamborini

Here we describe the synthesis and purification of Au nanoplates grown directly on surfaces by a chemical seed-mediated growth method. The synthesis involves the attachment of 3-5 nm diameter Au nanoparticle (NP) seeds onto glass and Si/SiOx surfaces and their subsequent growth into larger Au nanostructures by the chemical reduction of AuCl4- with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB). We used two different growth solutions. Growth solution 1 (GS1) led to a sample with 74% Au nanospheres and 26% Au nanoplates, while growth solution 2 (GS2), with lower CTAB and higher ascorbic acid concentration, led to 56% nanospheres and 44% nanoplates. The average wavelength of maximum extinction (lambdamax) of the localized surface plasmon resonance (LSPR) band of these samples was 549 and 627 nm, respectively. The use of adhesive tape or sonication enables the preferential removal of spherical Au nanostructures in both cases, leaving samples with >90% Au nanoplates. The average lambdamax increased to 672 nm (GS1) and 664 nm (GS2) for taped samples and 780 nm (GS1) and 720 nm (GS2) for sonicated samples, consistent with a higher purity of Au nanoplates on the surface. In all cases, the purified nanoplates vary in size and shape, including triangular, circular, or hexagonal structures, leading to broad spectra or the appearance of multiple peaks. We tuned the average lambdamax of the LSPR band of the Au nanoplate samples from 540 to 780 nm by varying the sonication time from 0 to 135 s. The change in lambdamax upon binding of anti-IgG to the edges of the purified nanoplates increases with an increasing number of anti-IgG on the edges, is 4-8 times larger compared to that of spherical nanoparticles, and is larger for samples purified by sonication compared to taping because the former has a larger initial lambdamax. A sample of Au nanoplates purified by taping and functionalized with anti-IgG at the edge sites displayed a shift in lambdamax as large as 45 nm for a 10 pg/mL solution of IgG (<1 pM).


Analytical Chemistry | 2010

Electrochemical Size Discrimination of Gold Nanoparticles Attached to Glass/Indium-Tin-Oxide Electrodes by Oxidation in Bromide-Containing Electrolyte

Olga S. Ivanova; Francis P. Zamborini

Here we describe the electrochemical oxidation of an assembly of gold nanoparticles (Au NPs) attached to glass/indium-tin-oxide (ITO) electrodes as a function of particle size. We synthesized Au NP arrays with NP diameters ranging from 8 to 250 nm by electrodeposition of Au from HAuCl(4) in H(2)SO(4) at potentials of -0.2 to 0.8 V versus Ag/AgCl using chronocoulometry to keep the amount of Au deposited constant. The average Au NP size increased with increasing deposition potential. The chemical reduction of HAuCl(4) by NaBH(4) in trisodium citrate solution led to 4 nm average diameter Au NPs, which we chemisorbed to the glass/ITO electrode. Linear sweep voltammograms (LSVs) obtained on the glass/ITO/Au NP (4 to 250 nm) electrodes (with a constant coverage of Au in terms of Au atoms per cm(2)) from 0.5 to 1.1 V in 0.01 M potassium bromide plus 0.1 M HClO(4) showed a positive shift in oxidation potential from 734 +/- 1 mV to 913 +/- 19 mV with increasing Au NP diameter. The shift agrees qualitatively with that predicted by a shift in the redox potential based on a difference in free energy associated with a change in surface energy as a function of particle size. On the basis of the charge during Au deposition versus the charge during oxidation, the oxidation process produces a mixture of Au(III)Br(4)(-) (25%) and Au(I)Br(2)(-) (75%). A glass/ITO electrode coated with a mixture of 4 and 250 nm Au NPs revealed 2 oxidation peaks, consistent with the two Au NP size populations present on the surface.


Faraday Discussions | 2004

Growth, conductivity, and vapor response properties of metal ion-carboxylate linked nanoparticle films

Michael C. Leopold; Robert L. Donkers; Dimitra Georganopoulou; Megan Fisher; Francis P. Zamborini; Royce W. Murray

Nanoparticles of metals (Au, Ag, Pd, alloys) in the size range 1-3 nm diameter can be stabilized against aggregation of the metal particles by coating the metal surface with a dense monolayer of ligands (thiolates). The stabilization makes it possible to analytically define the nanoparticle composition (for example, Au140(hexanethiolate)53, I) and to elaborate the chemical functionality of the protecting monolayer (for example, Au140(C6)35(MUA)18, II, where C6 = hexanethiolate and MUA = mercaptoundecanoic acid). Network polymer films (IIfilm) on interdigitated array electrodes can be prepared from II, based on cation coordination (i.e., Cu2+, Zn2+, Ag+, methyl viologen) by the carboxylates of MUA. The electronic conductivity of the IIfilm network polymer films occurs by electron hopping between the Au140 nanoparticle cores, and offers an avenue for investigation of metal-to-metal nanoparticle electron transfer chemistry. The report begins with a brief summary of what is known about metal nanoparticle electron transfer chemistry. The investigation goes on to assess factors that influence the dynamics of film formation as well as film conductivity, in the interest of better understanding the parameters affecting electron hopping rates in IIfilm network polymer films. Finally, sorption of organic vapors into IIfilm causes a decreased electronic conductivity and increased mass that can be assessed using quartz crystal microbalance measurements. The change in electronic conductivity can be exploited for the sensing of organic vapors.


Analytical Chemistry | 1999

Dendrimer-Mediated Adhesion between Vapor-Deposited Au and Glass or Si Wafers.

Lane A. Baker; Francis P. Zamborini; and Li Sun; Richard M. Crooks

Here, we report the use of amine-terminated poly(amidoamine) (PAMAM) dendrimers as adhesion promoters between vapor-deposited Au films and Si-based substrates. This method is relatively simple, requiring only substrate cleaning, dipping, and rinsing. Proof of concept is illustrated by coating glass slides and single-crystal Si wafers with monolayers of PAMAM dendrimers and then evaporating adherent, 150-nm-thick Au films atop the dendritic adhesion promoter. Scanning tunneling microscopy and cyclic voltammetry have been used to assess the surface roughness and electrochemical stability of the Au films. The effectiveness of the dendrimer adhesion layer is demonstrated using standard adhesive-tape peel tests.


Journal of the American Chemical Society | 2012

Oxidation of highly unstable <4 nm diameter gold nanoparticles 850 mV negative of the bulk oxidation potential.

Rafael A. Masitas; Francis P. Zamborini

Here we describe the oxidation of <4 nm diameter Au nanoparticles (NPs) attached to indium tin oxide-coated glass electrodes in Br(-) and Cl(-) solution. Borohydride reduction of AuCl(4)(-) in the presence of hexanethiol or trisodium citrate (15 min) led to Au NPs <4 nm in diameter. After electrochemical and ozone removal of the hexanthiolate ligands from the thiol-coated Au NPs, Au oxidation peaks appeared in the range 0-400 mV vs Ag/AgCl (1 M KCl), which is 850-450 mV negative of the bulk Au oxidation peak near 850 mV. The oxidation potential of citrate-coated Au NPs is in the 300-500 mV range and those of 4 and 12 nm diameter Au NPs in the 660-780 mV range. The large negative shift in potential agrees with theory for NPs in the 1-2 nm diameter range. The oxidation potential of Au in Cl(-) solution is positive of that in Br(-) solution, but the difference decreases dramatically as the NP size decreases, showing less dependence on the halide for smaller NPs.

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Royce W. Murray

University of North Carolina at Chapel Hill

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Francisco J. Ibañez

National University of La Plata

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Richard M. Crooks

University of Texas at Austin

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Radhika Dasari

University of Louisville

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Jocelyn F. Hicks

University of North Carolina at Chapel Hill

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