Papers by Donald Robinson
Rapidly expanding research in nanotechnology has led to exciting progress in a versatile array of... more Rapidly expanding research in nanotechnology has led to exciting progress in a versatile array of applications from medical diagnostics to photocatalytic fuel cells. Such success is due to the ability of researchers to manipulate the desired properties of nanomaterials by controlling their size, shape, and composition. Among the most thriving areas of nanoparticle research has been the synthesis and characterization of stable metallic nanoclusters capped by thiolate ligands. Our group has extended this research to study copper, silver, and gold clusters with remarkable stability and energetics, which was achieved by using dithiolates as the ligand stabilizers. In addition to the enhanced stability offered by the chelate effect, the use of dithiolate ligands instead of monothiolates is proposed to provide an alternate interfacial bond structure that is shown to strongly influence energetic properties of nanoclusters, with strong evidence of metalligand charge transfer. Energetic prop...
Faraday Discussions, 2018
The stochastic nature of very fast single-entity events challenges current electrochemical method... more The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors’ laboratory.
Journal of the American Chemical Society, Jan 22, 2016
The dynamic collision behavior of the electro-oxidation of single Ag nanoparticles is observed at... more The dynamic collision behavior of the electro-oxidation of single Ag nanoparticles is observed at Au microelectrodes using stochastic single-nanoparticle collision amperometry. Results show that an Ag nanoparticle collision/oxidation event typically consists of a series of 1 to ∼10 discrete "sub-events" over an ∼20 ms interval. Results also show that the Ag nanoparticles typically undergo only partial oxidation prior to diffusing away from the Au electrode into the bulk solution. Both behaviors are characterized and shown to exist under a variety of experimental conditions. These previously unreported behaviors suggest that nanoparticle collision and electro-dissolution is a highly dynamic process driven by fast particle-electrode interactions and nanoparticle diffusion.
Faraday Discussions, 2016
Here we investigate the mechanistic aspects of Pt nanoparticle (NP) aggregation in solutions typi... more Here we investigate the mechanistic aspects of Pt nanoparticle (NP) aggregation in solutions typically used for detecting NP/electrode impacts by electrocatalytic amplification (ECA). We previously proposed a general mechanism for Pt colloid destabilization that involved the participation of both the hydrazine redox probe and the pH buffer species as coagulants. Herein the Pt NP coagulation and aggregation mechanisms were further investigated with microscopic kinetic NP concentration monitoring and zeta potential measurements using nanoparticle tracking analysis (NTA), as well as open circuit potential experiments with a citrate-treated polycrystalline Pt surface to assess electrical double layer potential. After considering the combined results of these experiments we propose that the colloidal stability of citrate-capped platinum nanoparticles involves much more than the typical physicochemical interactions predicted by DLVO theory. A structure based on intermolecular H-bonding in...
The Journal of Physical Chemistry Letters, 2016
Herein the problem of colloidal instability on electrochemically detected nanoparticle (NP) colli... more Herein the problem of colloidal instability on electrochemically detected nanoparticle (NP) collisions with a Hg ultramicroelectrode (UME) by electrocatalytic amplification is addressed. NP tracking analysis (NTA) shows that rapid aggregation occurs in solution after diluting citrate-stabilized Pt NPs with hydrazine/phosphate buffers of net ionic strength greater than 70 mM. Colloidal stability improves by lowering the ionic strength, indicating that aggregation processes were strongly affected by charge screening of the NP double layer interactions at high cation concentrations. For the system of lowest ionic strength, the overwhelming majority of observed electrocatalytic current signals represent single NP/electrode impacts, as confirmed by NTA kinetic monitoring. NP diffusion coefficients determined by NTA and NP impact electroanalysis are in excellent agreement for the stable colloids, which signifies that the sticking probability of Pt NPs interacting with Hg is unity and that the observed NP impact rate agrees with the expected steady-state diffusive flux expression for the spherical cap Hg UME.
Uniform epitaxial growth of Pt on Fe3O4 nanoparticles; synergetic enhancement to Pt activity for the oxygen reduction reaction
Journal of Materials Chemistry A, 2013
ACS Nano, 2015
An integrated microfluidic/magnetophoretic methodology was developed for improving signal respons... more An integrated microfluidic/magnetophoretic methodology was developed for improving signal response time and detection limits for the chronoamperometric observation of discrete nanoparticle/electrode interactions by electrocatalytic amplification. The strategy relied on Pt-decorated iron oxide nanoparticles which exhibit both superparamagnetism and electrocatalytic activity for the oxidation of hydrazine. A wet chemical synthetic approach succeeded in the controlled growth of Pt on the surface of FeO/ Fe 3 O 4 core/shell nanocubes, resulting in highly uniform Pt-decorated iron oxide hybrid nanoparticles with good dispersibility in water. The unique mechanism of hybrid nanoparticle formation was investigated by electron microscopy and spectroscopic analysis of isolated nanoparticle intermediates and final products. Discrete hybrid nanoparticle collision events were detected in the presence of hydrazine, an electrochemical indicator probe, using a gold microband electrode integrated into a microfluidic channel. In contrast with related systems, the experimental nanoparticle/electrode collision rate correlates more closely with simple theoretical approximations, primarily due to the accuracy of the nanoparticle tracking analysis method used to quantify nanoparticle concentrations and diffusion coefficients. Further modification of the microfluidic device was made by applying a tightly focused magnetic field to the detection volume to attract the magnetic nanoprobes to the microband working electrode, thereby resulting in a 6-fold increase to the relative frequency of chronoamperometric signals corresponding to discrete nanoparticle impact events.
Tunable Intervalence Charge Transfer in Ruthenium Prussian Blue Analog Enables Stable and Efficient Biocompatible Artificial Synapses
Advanced Materials
Emerging concepts for neuromorphic computing, bioelectronics, and brain‐computer interfacing insp... more Emerging concepts for neuromorphic computing, bioelectronics, and brain‐computer interfacing inspire new research avenues aimed at understanding the relationship between oxidation state and conductivity in unexplored materials. This report expands the materials playground for neuromorphic devices to include a mixed valence inorganic 3D coordination framework, a ruthenium Prussian blue analog (RuPBA), for flexible and biocompatible artificial synapses that reversibly switch conductance by more than four orders of magnitude based on electrochemically tunable oxidation state. The electrochemically tunable degree of mixed valency and electronic coupling between N‐coordinated Ru sites controls the carrier concentration and mobility, as supported by density functional theory computations and application of electron transfer theory to in situ spectroscopy of intervalence charge transfer. Retention of programmed states is improved by nearly two orders of magnitude compared to extensively st...
Uploads
Papers by Donald Robinson