Publications by authors named "Dan Bizzotto"

23 Publications

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Correlating structural assemblies of photosynthetic reaction centers on a gold electrode and the photocurrent - potential response.

iScience 2021 May 4;24(5):102500. Epub 2021 May 4.

Advanced Materials and Process Engineering Laboratory, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.

The use of biomacromolecules is a nascent development in clean alternative energies. In applications of biosensors and biophotovoltaic devices, the bacterial photosynthetic reaction center (RC) is a protein-pigment complex that has been commonly interfaced with electrodes, in large part to take advantage of the long-lived and high efficiency of charge separation. We investigated assemblies of RCs on an electrode that range from monolayer to multilayers by measuring the photocurrent produced when illuminated by an intensity-modulated excitation light source. In addition, atomic force microscopy and modeling of the photocurrent with the Marcus-Hush-Chidsey theory detailed the reorganization energy for the electron transfer process, which also revealed changes in the RC local environment due to the adsorbed conformations. The local environment in which the RCs are embedded significantly influenced photocurrent generation, which has implications for electron transfer of other biomacromolecules deposited on a surface in sensor and photovoltaic applications employing a redox electrolyte.
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http://dx.doi.org/10.1016/j.isci.2021.102500DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8170006PMC
May 2021

Thermal Stability of Thiolated DNA SAMs in Buffer: Revealing the Influence of Surface Crystallography and DNA Coverage via In Situ Combinatorial Surface Analysis.

Langmuir 2020 12 24;36(48):14495-14506. Epub 2020 Nov 24.

Advanced Materials and Process Engineering Laboratory (AMPEL), University of British Columbia, Vancouver V6T 1Z4, Canada.

The thermal stability of thiol based DNA SAMs prepared on gold surfaces is an important parameter that is correlated to sensor lifetime. The thermal stability of DNA SAMs was evaluated in aqueous buffer through the use of fluorophore labeled DNA, a single crystal gold bead electrode, and microscopy. The stability of different crystallographic regions on the electrode was studied for thermal treatments up to 95 °C for 90 min. Using a combinatorial surface analytical measurement showed that the crystallography of the underlying gold surface played a significant role, with the square or rectangular lattices (e.g., 110, 100, 210) having the highest stability. Surfaces with hexagonal lattices (e.g., 111, 311, 211) were less stable toward thermal treatments. These crystallographic trends were observed for both high and low coverage DNA SAMs. High coverage DNA SAMs were the most stable, with stability decreasing with decreasing coverage on average. Increasing DNA SAM coverage appears to slow the kinetics of thermal desorption, but the coordination to the underlying surface determined their relative stability. Preparing the DNA SAMs under nominally similar conditions were found to create surfaces that were similar at room temperature, but had significantly different thermal stability. Optimal DNA sensing with these surfaces most often requires low coverage DNA SAMs which results in poor thermal stability, which is predictive of a poor shelf life, making optimization of both parameters challenging. Furthermore, the crystallographically specific results should be taken into account when studying the typically used polycrystalline substrates since the underlying surface crystallography maybe different for different samples. It appears that preparing DNA SAMs with low coverage and significant thermal stability will be challenging using the current SAM preparation procedures.
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http://dx.doi.org/10.1021/acs.langmuir.0c01828DOI Listing
December 2020

Measuring and Controlling the Local Environment of Surface-Bound DNA in Self-Assembled Monolayers on Gold When Prepared Using Potential-Assisted Deposition.

Langmuir 2020 06 14;36(24):6837-6847. Epub 2020 Jun 14.

AMPEL, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.

DNA self-assembled monolayers (SAMs) were prepared using potential-assisted deposition on clean gold single-crystal bead electrodes under a number of conditions (constant or square-wave potential perturbations in TRIS or phosphate immobilization buffers with and without Cl). The local environment around the fluorophore-labeled DNA tethered to the electrode surface was characterized using in situ fluorescence microscopy during electrochemical measurements as a function of the underlying surface crystallography. Potential-assisted deposition from a TRIS buffer containing Cl created DNA SAMs that were uniformly distributed on the surface with little preference to the underlying crystallography. A constant (+0.4 V/SCE) or a square-wave potential perturbation (+0.4 to -0.3 V/SCE, 50 Hz) resulted in similar DNA-modified surfaces in TRIS immobilization buffer. Deposition using a square-wave potential without Cl resulted in lower DNA surface coverage. Despite this, the local environment around the DNA in the SAM appears to be densely packed. This implies the formation of clusters of densely packed DNA in the SAM. This effect was also demonstrated when depositing from a phosphate buffer. DNA clusters were significantly reduced when Cl was present in the buffer. Clusters were most prevalent on the low-index plane surfaces (e.g., {111} and {100}) and less on the higher-index planes (e.g., {210} or {311}). A mechanism is proposed to rationalize the formation of DNA-clustered regions for deposition using a square-wave potential perturbation. The conditions for creating clusters of DNA in a SAM or for preventing these clusters from forming provide an approach for tailoring the surfaces used for biosensing.
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http://dx.doi.org/10.1021/acs.langmuir.9b03970DOI Listing
June 2020

Electrodepositing DNA Self-Assembled Monolayers on Au: Detailing the Influence of Electrical Potential Perturbation and Surface Crystallography.

ACS Sens 2019 02 5;4(2):513-520. Epub 2019 Feb 5.

The preparation of DNA self-assembled monolayers (SAMs) on single-crystal gold bead electrodes using an applied potential is evaluated with in situ electrochemical fluorescence microscopy. Applying a constant deposition potential or a square-wave potential perturbation during the formation of DNA SAMs is compared for two different modification methods: DNA SAM formation on a clean gold surface followed by alkythiol backfilling (as is typically done in the literature) or via thiol-exchange on an alkylthiol-modified gold surface. DNA SAMs prepared from a chloride-containing deposition buffer were not significantly different when using either square-wave potential perturbation or at a constant applied potential even when considering different surface crystallographies. Greater variations were observed when applying more positive potentials for both DNA thiol-exchange and DNA adsorption on clean Au. Our results suggest that using either a constant potential or a square-wave potential perturbation for 5 min both create defects by weakening the gold-thiol interaction. When the deposition is performed with the adsorption of chloride ions from the electrolyte, the electrodeposition results in a similar increase in DNA coverage when compared to depositions performed at open circuit potentials.
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http://dx.doi.org/10.1021/acssensors.8b01695DOI Listing
February 2019

Direct Mapping of Heterogeneous Surface Coverage in DNA-Functionalized Gold Surfaces with Correlated Electron and Fluorescence Microscopy.

Langmuir 2018 02 6;34(7):2425-2431. Epub 2018 Feb 6.

Advanced Materials and Proceess Engineering Laboratory (AMPEL) and ‡Department of Chemistry, University of British Columbia , Vancouver V6T 1Z1, Canada.

The characterization of biofunctionalized surfaces such as alkanethiol self-assembled monolayers (SAMs) on gold modified with DNA or other biomolecules is a challenging analytical problem, and access to a routine method is desirable. Despite substantial investigation from structural and mechanistic perspectives, robust and high-throughput metrology tools for SAMs remain elusive but essential for the continued development of these devices. We demonstrate that scanning electron microscopy (SEM) can provide image contrast of the molecular interface during SAM functionalization. The high-speed, large magnification range, and ease of use make this widely available technique a powerful platform for measuring the structure and composition of SAM surfaces. This increased throughput allows for a better understanding of the nonideal spatial heterogeneity characteristic of SAMs utilized in real-world conditions. SEM image contrast is characterized through the use of fluorescently labeled DNA, which enables correlative SEM and fluorescence microscopy. This allows identification of the DNA-modified regions at resolutions that approach the size of the biomolecule. The effect of electron beam irradiation dose is explored, which leads to straightforward lithographic patterning of DNA SAMs with nanometer resolution and with control over the surface coverage of specifically adsorbed DNA.
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http://dx.doi.org/10.1021/acs.langmuir.7b03766DOI Listing
February 2018

Beyond Simple Cartoons: Challenges in Characterizing Electrochemical Biosensor Interfaces.

ACS Sens 2018 01 12;3(1):5-12. Epub 2018 Jan 12.

Department of Chemistry, Simon Fraser University , Burnaby, BC V5A 1S6, Canada.

Design and development of surface-based biosensors is challenging given the multidisciplinary nature of this enterprise, which is certainly the case for electrochemical biosensors. Self-assembly approaches are used to modify the surface with capture probes along with electrochemical methods for detection. Complex surface structures are created to improve the probe-target interaction. These multicomponent surface structures are usually idealized in schematic representations. Many rely on the analytical performance of the sensor surface as an indication of the quality of the surface modification strategy. While directly linked to the eventual device, arguments for pursuing a more extensive characterization of the molecular environments at the surface are presented as a path to understanding how to make electrochemical sensors that are more robust, reliable with improved sensitivity. This is a complex task that is most often accomplished using methods that only report the average characteristics of the surface. Less often applied are methods that are sensitive to the probe (or adsorbate) present in nonideal configurations (e.g., aggregates, clusters, nonspecifically adsorbed). Though these structures may compose a small fraction of the overall modified surface, they have an uncertain impact on sensor performance and reliability. Addressing this issue requires application of imaging methods over a variety of length scales (e.g., optical microscopy and/or scanning probe microscopy) that provide valuable insight into the diversity of surface structures and molecular environments present at the sensing interface. Furthermore, using in situ analytical methods, while complex, can be more relevant to the sensing environment. Reliable measurements of the nature and extent of these features are required to assess the impact of these nonideal configurations on the sensing process. The development and use of methods that can characterize complex surface based biosensors is arguably required, highlighting the need for a multidisciplinary approach toward the preparation and analysis of the biosensor surface. In many ways, representing the surface without reliance on overly simplified cartoons will highlight these important considerations for improving sensor characteristics.
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http://dx.doi.org/10.1021/acssensors.7b00840DOI Listing
January 2018

Quantifying the Selective Modification of Au(111) Facets via Electrochemical and Electroless Treatments for Manipulating Gold Nanorod Surface Composition.

Langmuir 2017 11 1;33(45):12887-12896. Epub 2017 Nov 1.

AMPEL, ‡Department of Chemistry, and §Department of Physics and Astronomy, University of British Columbia , Vancouver, BC V6T 1Z4, Canada.

Manipulating the composition of a mixed alkylthiol self-assembled monolayer (SAM) modified gold surface using both electrochemical and electroless methods is demonstrated. Through the use of fluorophore labeled thiolated DNA and in situ fluorescence microscopy with a gold single crystal bead electrode, a procedure was developed to study and quantify the selective desorption of an alkylthiolate SAM. This method enabled a self-consistent measurement of the removal of the SAM from the 111 surface compared to the 100 surface region at various potentials. A 20-fold increase in the electrochemical removal and replacement of the SAM from the 111 surface over the 100 surface was realized at -0.8 V/AgAgCl. A related procedure was developed for the solution-based electroless removal of the SAM using NaBH achieving a similar selectivity at the same potential. Unfortunately, in the electroless process fine control over the reducing potential was difficult to achieve. In addition, working in the presence of O complicates the solution potential measurement due to depolarization by the reduction of O, resulting in a less clear relationship between selectivity and measured solution potential. Interestingly, the electrochemical method was not disturbed by the presence of O. In preparation for work with Au nanorods, electrochemical measurements were performed in electrolyte that included 1 mM CTAB and was found to not interfere with this method. Preliminary results are promising for using this methodology for treatment of acid-terminated alkylthiol modified Au nanorods.
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http://dx.doi.org/10.1021/acs.langmuir.7b03021DOI Listing
November 2017

Measuring and Remediating Nonspecific Modifications of Gold Surfaces Using a Coupled in Situ Electrochemical Fluorescence Microscopic Methodology.

Anal Chem 2017 01 16;89(1):886-894. Epub 2016 Dec 16.

AMPEL, Department of Chemistry, The University of British Columbia , Vancouver, British Columbia V6T 1Z4, Canada.

In surface-based biosensors, the nonspecific or undesired adsorption of the probe is an important characteristic that is typically difficult to measure and therefore to control or eliminate. A methodology for measuring and then minimizing or eliminating this problem on gold surfaces, readily applicable to many common surface modifications is presented. Combining electrochemical perturbation and fluorescence microscopy, we show that the potential at which the adsorbed species is removed can be used as an estimate of the strength of the adsorbate-surface interaction. This desorption potential can be easily measured through an increase in fluorescence intensity as the potential is manipulated. Furthermore, this method can be used to evaluate strategies for preventing or removing nonspecific adsorption. This is demonstrated for a wide variety of surface modifications, from strongly chemisorbed monolayers such as thiol self-assembled monolayers (SAMs) to physisorbed monolayers as well as for complex surface structures like peptide and DNA mixed-component SAMs. The use of a coadsorption strategy or small magnitude potential-step cycles was shown to significantly decrease the amount of nonspecifically or noncovalently bound probe, creating better defined surfaces.
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http://dx.doi.org/10.1021/acs.analchem.6b03953DOI Listing
January 2017

Potential Controls the Interaction of Liposomes with Octadecanol-Modified Au Electrodes: An in Situ AFM Study.

Langmuir 2015 Nov 12;31(46):12797-806. Epub 2015 Nov 12.

AMPEL, Department of Chemistry, University of British Columbia , Vancouver, British Columbia V6T 1Z4, Canada.

The formation of supported lipid bilayers using liposomes requires interaction with the solid surface, rupture of the liposome, and spreading to cover the surface with a lipid bilayer. This can result in a less-than-uniform coating of the solid surface. Presented is a method that uses the electrochemical poration of an adsorbed lipid-like layer on a Au electrode to control the interaction of 100 nm DOPC liposomes. An octadecanol-coated Au-on-mica surface was imaged using tapping-mode AFM during the application of potential in the presence or absence of liposomes. When the substrate potential was made negative enough, defects formed in the adsorbed layer and new taller features were observed. More features were observed and existing features increased in size with time spent at this negative poration potential. The new features were 1.8-2.0 nm higher than the octadecanol-coated gold surface, half the thickness of a DOPC bilayer. These features were not observed in the absence of liposomes when undergoing the same potential perturbation. In the presence of liposomes, the application of a poration potential was needed to initiate the formation of these taller features. Once the applied potential was removed, the features stopped growing and no new regions were observed. The size of these new regions was consistent with the footprint of a flattened 100 nm liposome. It is speculated that the DOPC liposomes were able to interact with the defects and became soluble in the octadecanol, creating a taller region that was limited in size to the liposome that adsorbed and became incorporated. This AFM study confirms previous in situ fluorescence measurements of the same system and illustrates the use of a potential perturbation to control the formation of these regions of increased DOPC content.
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http://dx.doi.org/10.1021/acs.langmuir.5b03605DOI Listing
November 2015

Influence of surface structure on single or mixed component self-assembled monolayers via in situ spectroelectrochemical fluorescence imaging of the complete stereographic triangle on a single crystal Au bead electrode.

J Am Chem Soc 2015 Jan 24;137(1):276-88. Epub 2014 Dec 24.

AMPEL, ‡Department of Chemistry, University of British Columbia , Vancouver, British Columbia V6T 1Z1, Canada.

The use of a single crystal gold bead electrode is demonstrated for characterization of self-assembled monolayers (SAM)s formed on the bead surface expressing a complete set of face centered cubic (fcc) surface structures represented by a stereographic projection. Simultaneous analysis of many crystallographic orientations was accomplished through the use of an in situ fluorescence microscopic imaging technique coupled with electrochemical measurements. SAMs were prepared from different classes of molecules, which were modified with a fluorescent tag enabling characterization of the influence of electrical potential and a direct comparison of the influence of surface structure on SAMs adsorbed onto low index, vicinal and chiral surfaces. The assembly of alkylthiol, Aib peptide and DNA SAMs are studied as a function of the electrical potential of the interface revealing how the organization of these SAMs depend on the surface crystallographic orientation, all in one measurement. This approach allows for a simultaneous determination of SAMs assembled onto an electrode surface onto which the whole fcc stereographic triangle can be mapped, revealing the influence of intermolecular interactions as well as the atomic arrangement of the substrate. Moreover, this method enables study of the influence of the Au surface atom arrangement on SAMs that were created and analyzed, both under identical conditions, something that can be challenging for the typical studies of this kind using individual gold single crystal electrodes. Also demonstrated is the analysis of a SAM containing two components prepared using thiol exchange. The two component SAM shows remarkable differences in the surface coverage, which strongly depends on the surface crystallography enabling estimates of the thiol exchange energetics. In addition, these electrode surfaces enable studies of molecular adsorption onto the symmetry related chiral surfaces since more than one stereographic triangle can be imaged at the same time. The ability to observe a SAM modified surface that contains many complete fcc stereographic triangles will facilitate the study of the single and multicomponent SAMs, identifying interesting surfaces for further analysis.
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http://dx.doi.org/10.1021/ja5104475DOI Listing
January 2015

Potential-dependent interaction of DOPC liposomes with an octadecanol-covered Au(111) surface investigated using electrochemical methods coupled with in situ fluorescence microscopy.

Langmuir 2013 Mar 27;29(10):3347-60. Epub 2013 Feb 27.

Advanced Materials and Process Engineering Laboratory (AMPEL), Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada.

The potential-controlled incorporation of DOPC liposomes (100 nm diameter) into an adsorbed octadecanol layer on Au(111) was studied using electrochemical and in situ fluorescence microscopy. The adsorbed layer of octadecanol included a small amount of a lipophilic fluorophore-octadecanol modified with BODIPY-to enable fluorescence imaging. The deposited octadecanol layer was found not to allow liposomes to interact unless the potential was less than -0.4 V/SCE, which introduces defects into the adsorbed layer. Small increases in the capacitance of the adsorbed layer were measured after introducing the defects, allowing the liposomes to interact with the defects and then annealing the defects at 0 V/SCE. A change in the adsorbed layer was also signified by a more positive desorption potential for the liposome-modified adsorbed layer as compared to that for an adsorbed layer that was porated in a similar fashion but without liposomes present in the electrolyte. These subtle changes in capacitance are difficult to interpret, so an in situ spectroscopic study was performed to provide a more direct measure of the interaction. The incorporation of liposomes should result in an increase in the fluorescence measured because the fluorophore should become further separated from the gold surface, reducing the efficiency of fluorescence quenching. No significant increase in the fluorescence of the adsorbed layer was observed during the potential pulses used in the poration procedure in the absence of liposomes. In the presence of liposomes, the fluorescence intensity was found to depend on the potential and time used for poration. At 0 V/SCE, no significant change in the fluorescence was observed for defect-free adsorbed layers. Changing the poration potential to -0.4 V/SCE caused significant increases in the fluorescence and the appearance of new structural features in the adsorbed layers that were more easily observed during the desorption procedure. The extent of fluorescence changes was found to be strongly dependent on the nature of the adsorbed layer under investigation, which suggests that the poration and liposome interaction are dependent on the quality of the adsorbed layer and its ease of poration through changes in the electrode potential.
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http://dx.doi.org/10.1021/la400042cDOI Listing
March 2013

What happens to the thiolates created by reductively desorbing SAMs? An in situ study using fluorescence microscopy and electrochemistry.

Langmuir 2013 Feb 29;29(6):2065-74. Epub 2013 Jan 29.

Department of Chemistry, AMPEL, University of British Columbia, Vancouver, Canada.

In situ examination of the reductive desorption process for Au microelectrodes modified with a thiol self-assembled monolayer (SAM) using fluorescence microscopy enabled the study of the fate of the desorbed thiolate species. The Bodipy labeled alkyl-thiol SAM, when adsorbed, is not fluorescent due to quenching by the Au surface. Once reductively desorbed, the thiolate molecules fluoresce and their direction and speed are monitored. At moderately negative reduction potentials, the thiolate species hemispherically diffuse away from the microelectrode. Also observed is the influence of a closely positioned counter electrode on the direction of the desorbed thiolate movement. As the potential becomes more negative, the molecules move in an upward direction, with a speed that depends on the amount of dissolved H(2) produced by water reduction. Shown is that this motion is controlled, in large part, by the change in the electrolyte density near the electrode due to dissolved H(2). These results should help in explaining the extent of readsorption at oxidative potentials observed in cyclic voltammetry (CV) reductive desorption measurements, as well as improving the general understanding of the SAM removal process by reductive desorption. The electrogenerated H(2) was also shown to be able to reductively remove the thiol SAM from the Pt/Ir particles that decorate the microelectrode glass sheath.
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http://dx.doi.org/10.1021/la305170cDOI Listing
February 2013

On the nature of DNA self-assembled monolayers on Au: measuring surface heterogeneity with electrochemical in situ fluorescence microscopy.

J Am Chem Soc 2009 Mar;131(11):4042-50

Advanced Materials and Process Engineering Laboratory, Department of Chemistry, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.

The creation of gold surfaces modified by single- or double-stranded DNA self-assembled monolayers (SAMs) is shown to produce heterogeneous surface packing densities through the use of electrochemical studies coupled with fluorescence imaging. The modified surfaces created by direct adsorption of thiolate DNA [followed by passivation with mecaptohexanol (MCH)] resulted in regions covered by a monolayer of DNA SAM and other regions that were coated by large particles of DNA. The difference in fluorescence intensity measured from these regions was dramatic. More importantly, a regional variance in fluorescence intensity in response to electrochemical potential was observed: the large aggregates showing a significantly different modulation of fluorescence intensity than the monolayer-coated regions. Electrochemical desorption and detection of the fluorescently tagged DNA provided clear evidence of a complete surface modification. These studies have implications for biosensor/biochip development using DNA SAMs. A modification in the method used to produce the DNA SAMs resulted in a significantly different surface with much fewer aggregates and more significant electromodulation of the fluorescence intensity, though at much lower DNA surface density (ca. 1% of maximum theoretical coverage). This method for forming the modified surfaces has clear advantages over the currently accepted practice and emphasizes the importance of studying the nonaveraged nature of the sensor surface using in situ imaging tools like electrofluorescence microscopy.
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http://dx.doi.org/10.1021/ja808696pDOI Listing
March 2009

Fluorescence imaging of the oxidative desorption of a BODIPY-alkyl-thiol monolayer coated Au bead.

Langmuir 2008 Aug 21;24(15):7881-8. Epub 2008 Jun 21.

Department of Chemistry, Advanced Materials and Process Engineering Laboratory (AMPEL), University of British Columbia, Vancouver, British Columbia, Canada.

The reductive and oxidative desorption of a BODIPY labeled alkylthiol self-assembled monolayer (SAM) on Au was studied using electrochemical methods coupled with fluorescence microscopy and image analysis procedures to monitor the removal of the adsorbed layer. Two SAMs were formed using two lengths of the alkyl chain (C10 and C16). The BODIPY fluorescent moiety used is known to form dimers which through donor-acceptor energy transfer results in red-shifted fluorescence. Fluorescence from the monomer and dimer were used to study the nature of the desorbed molecules during cyclic step changes in potential. The reductive desorption was observed to occur over a small potential window (0.15 V) signified by an increase in capacitance and in fluorescence. Oxidative readsorption was also observed through a decrease in capacitance and a lack of total removal of the fluorescent layer. Removal by oxidative desorption occurred at positive potentials over a broad potential range near the oxidation of the bare Au. The resulting fluorescence showed that the desorbed molecules remained near the electrode surface and were not dispersed over the 20 s waiting time. The rate of change of the fluorescence for oxidative desorption was much slower than the reductive desorption. Comparing monomer and dimer fluorescence intensities indicated that the dimer was formed on the Au surface and desorbed as a dimer, rather than forming from desorbed monomers near the electrode surface. The dimer fluorescence can only be observed through energy transfer from the excited monomer suggesting that the monomers and dimers must be in close proximity in aggregates near the electrode. The fluorescence yield for longer alkyl chain was always lower presumably due to its decreased solubility in the interfacial region resulting in a more efficient fluorescence quenching. The oxidative desorption process results in a significantly etched or roughened electrode surface suggesting the coupling of thiol oxidative removal and Au oxide formation which results in the removal of Au from the electrode.
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http://dx.doi.org/10.1021/la800233cDOI Listing
August 2008

Fluorescence of amphotericin B-deoxycholate (fungizone) monomers and aggregates and the effect of heat-treatment.

Langmuir 2007 Aug 18;23(17):8718-25. Epub 2007 Jul 18.

Advanced Materials and Process Engineering Laboratory, Department of Chemistry, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.

Fluorescence excitation and emission spectra are reported for the polyene macrolide antifungal agent Amphotericin B formulated as micellar dispersion Fungizone (FZ) and its modified counterpart heat-treated Fungizone. The addition of sodium dodecyl sulfate or sodium deoxycholate surfactant to modulate the aggregation state of Amphotericin B confirms that the monomer and dimer states have different fluorescence spectra. Energy transfer from excited dimer to monomer is observed. Both FZ and heat-treated FZ (HTFZ) show expected S1 --> S0 fluorescence emission as well as anti-Kasha fluorescence emission from the S2 state. The excitation and S1 --> S0 emission spectra of HTFZ are similar to those of FZ, while the S2 --> S0 fluorescence differs in intensity between them. The variation in the rate constant for internal conversion from S2 to S1 as the surfactant concentration is increased differs for FZ and HTFZ; we propose that this may form a new basis for examining the super-aggregated character of AmB preparations. FZ and HTFZ have a similar stability to disaggregation by added sodium dodecyl sulfate surfactant. These findings provide the groundwork for future fluorescence characterization of FZ or HTFZ interactions with cell membranes.
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http://dx.doi.org/10.1021/la7008573DOI Listing
August 2007

Characterization of mixed alcohol monolayers adsorbed onto a Au(111) electrode using electro-fluorescence microscopy.

Langmuir 2006 May;22(10):4869-76

Department of Chemistry, Advanced Materials and Process Engineering Laboratory (AMPEL), University of British Columbia, 2355 East Mall, Vancouver BC, Canada V6T 1Z4.

A single-crystal Au(111) electrode modified with an adsorbed layer of 1-octadecanol (C18OH) or oleyl alcohol (OLA) in pure or mixed composition was characterized using electrochemical and in situ fluorescence microscopy. Cyclic voltammetry and differential capacitance measurements revealed a repeatable, potential-induced adsorption/desorption process of the surfactant to/from the electrode surface while charge density and film pressure measurements indicated quasi-ideal mixing of the two adsorbed alcohols. A layer less defective than pure C18OH was created with incorporated OLA. Optical characterization was accomplished using epi-fluorescence microscopy combined with electrochemistry (electro-fluorescence microscopy) through the incorporation of two fluorescent probes into the adsorbed surfactant layer. Since molecular luminescence is quenched by a nearby metal, fluorescence was only observed when the fluorescent dye/alcohol layers were desorbed and therefore separated from the metal surface. When desorbed, the structure of the alcohol layers were similar in character, revealing aggregated features which did not change in morphology over numerous desorption/re-adsorption cycles. We have also used the electro-fluorescence technique to estimate the distance separating the metal and desorbed surfactant and believe that the molecules are displaced from the electrode surface by a distance not more than 40 nm.
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http://dx.doi.org/10.1021/la052994iDOI Listing
May 2006

Electrochemical formation of a Pt/Zn alloy and its use as a catalyst for oxygen reduction reaction in fuel cells.

J Phys Chem B 2006 May;110(17):8715-22

Department of Chemistry, Advanced Materials Process and Engineering Laboratory, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.

The characterization of an electrochemically created Pt/Zn alloy by Auger electron spectroscopy is presented indicating the formation of the alloy, the oxidation of the alloy, and the room temperature diffusion of the Zn into the Pt regions. The Pt/Zn alloy is stable up to 1.2 V/RHE and can only be removed with the oxidation of the base Pt metal either electrochemically or in aqua regia. The Pt/Zn alloy was tested for its effectiveness toward oxygen reduction. Kinetics of the oxygen reduction reaction (ORR) were measured using a rotating disk electrode (RDE), and a 30 mV anodic shift in the potential of ORR was found when comparing the Pt/Zn alloy to Pt. The Tafel slope was slightly smaller than that measured for the pure Pt electrode. A simple procedure for electrochemically modifying a Pt-containing gas diffusion electrode (GDE) with Zn was developed. The Zn-treated GDE was pressed with an untreated GDE anode, and the created membrane electrode assembly was tested. Fuel cell testing under two operating conditions (similar anode and cathode inlet pressures, and a larger cathode inlet pressure) indicated that the 30 mV shift observed on the RDE was also evident in the fuel cell tests. The high stability of the Pt/Zn alloy in acidic environments has a potential benefit for fuel cell applications.
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http://dx.doi.org/10.1021/jp055350sDOI Listing
May 2006

Novel electrophoresis mechanism based on synchronous alternating drag perturbation.

Electrophoresis 2005 Jan;26(1):82-90

Department of Physicsand Astronomy, University of British Columbia, Vancouver, BC, Canada.

We present a novel means of transporting molecules in solution by applying a zero-time-average alternating motive force to the molecules, and perturbing the molecular drag coefficient synchronously with the applied force, thus causing a net drift in a direction determined by the phase of the alternating drag perturbation relative to the alternating force. We apply an electrophoretic form of the method to transport and concentrate DNA in a gel, such that all molecules migrate on average away from the nearest electrode and toward a central region. Since an electrode does not occupy this central region, this method presents the possibility of transporting and focusing DNA and other charged molecules in regions free from electrodes and the associated electrochemistry.
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http://dx.doi.org/10.1002/elps.200406140DOI Listing
January 2005

Electrochemical dimerization of 2-(2'-thienyl)pyridine adsorbed on Au(111) observed by in situ fluorescence.

Langmuir 2004 Sep;20(19):8270-8

Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada.

The study of heterodentate molecules adsorbed on metal electrodes provides an opportunity to expand the functionality of modified surfaces while offering insights into the surface and intramolecular electronic interactions of organic adsorbates. The adsorption of 2-(2'-thienyl)pyridine, a molecule containing both pyridine and thiophene moieties, on a Au(111) electrode is reported. Adsorption was characterized by electrochemistry in neutral and basic aqueous electrolyte and was compared to that of pyridine. The aqueous electrochemistry of thiophene on Au(111) was also characterized for comparison purposes. At negative potentials, in the presence of 2-(2'-thienyl)pyridine, a diffuse, pi-bonded monolayer was formed, and a phase transition to a close-packed N- and/or S-bonded configuration was observed near -0.4 V in a 1 mM solution of adsorbate, similar to that seen in pyridine on Au(111). The thiophene-like oxidative dimerization of the molecule was confirmed at positive potentials using in situ fluorescence microscopy by comparison with the spectrum of the chemically synthesized dimer.
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http://dx.doi.org/10.1021/la0485024DOI Listing
September 2004

Selective reductive desorption of a SAM-coated gold electrode revealed using fluorescence microscopy.

J Am Chem Soc 2004 Jul;126(26):8329-35

Department of Chemistry, Advanced Materials & Process Engineering Laboratory (AMPEL), University of British Columbia, Vancouver, BC, Canada.

The reductive desorption of a self-assembled monolayer (SAM) of a fluorescent thiol molecule (BodipyC10SH) from Au was characterized using electrochemistry and epi-fluorescence microscopy. Molecular luminescence is quenched near a metal surface, so fluorescence was only observed for molecules reductively desorbed and then separated from the electrode surface. Fluorescence imaging showed that reductive desorption was selective, with desorption occurring from different regions of the Au electrode depending on the extent of the negative potential excursion. When desorbed, the molecules were sufficiently mobile, diffusing away from the electrode surface, thereby preventing oxidative readsorption. At sufficiently negative desorption potentials, all of the thiol was desorbed from the electrode surface, resulting in fluorescence at the air/solution interface. The selective removal of the thiol monolayer from distinct regions was correlated to features on the electrode surface and was explained through potential-dependent interfacial energies. This in situ electrofluorescence microscopy technique may be useful in sensor development.
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http://dx.doi.org/10.1021/ja0494095DOI Listing
July 2004

Effect of heat-treated amphotericin B on renal and fungal cytotoxicity.

Antimicrob Agents Chemother 2004 Jan;48(1):333-6

School of Occupational and Environmental Hygiene, Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.

The purpose of this investigation was to determine the cytotoxicity of amphotericin B (AMB; trade name Fungizone [FZ]) following the administration of FZ and a heat-treated form of FZ (HFZ) to LLC-PK(1) pig kidney cells and Cryptococcus neoformans var. gattii cells. HFZ was significantly less toxic to kidney cells than FZ at all concentrations tested. For both FZ and HFZ, the concentration range which resulted in a 50% reduction of the growth of fungal cells was 0.125 to 1 mg/ml. These findings suggest that heat treatment decreases AMB's renal cytotoxicity without modifying its antifungal activity.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC310175PMC
http://dx.doi.org/10.1128/AAC.48.1.333-336.2004DOI Listing
January 2004

Epi-fluorescence microscopic characterization of potential-induced changes in a DOPC monolayer on a Hg drop.

Analyst 2003 Jun;128(6):552-61

Department of Chemistry, Advanced Materials and Process Engineering Laboratory, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1.

Characterization of the potential-induced changes of a lipid-coated Hg-0.1 M KCl interface through electrochemical techniques and newly developed in situ fluorescence microscopy is described. Fluorescence of a fluorophore-containing dioleoyl phosphatidylcholine (DOPC) layer deposited from the gas-solution interface was observed to be dependent upon the potential of the Hg surface. The largest changes occurred for potentials where the lipid layer was desorbed: the lipid moved away from the electrode surface, reducing the efficiency of metal-mediated quenching of the excited state resulting in an increase in fluorescence. Electric potential-induced changes in the morphology of the adsorbed or desorbed DOPC lipid monolayer were observed optically for the first time using this technique. The observed potential-dependent fluorescence was compared to previous studies on an octadecanol-coated Au(111) electrode. Fluorescence microscopy was also used to characterize the fusion of DOPC liposomes with a previously adsorbed DOPC layer. Large changes in fluorescence were observed for the DOPC layer after fusion with liposomes. The fusion was accomplished via potential-created defects in the adsorbed DOPC monolayer through which the liposomes interact. The integration of the liposomes into the adsorbed monolayer results in a hybrid layer in which some lipid exists further from the electrode surface, resulting in a large increase in fluorescence. Possibilities for the creation of a biomimetic adsorbed hybrid lipid layer on Hg are also discussed.
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http://dx.doi.org/10.1039/b212924hDOI Listing
June 2003

Potential-controlled switching of 2-(2'-thienyl)pyridine adsorbed on Au(111).

Chem Commun (Camb) 2002 Dec(24):3026-7

Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, Canada V6T 1Z1.

Switching between three different adsorbed states was achieved using potential control to separately induce electrochemical behaviour associated with changes in binding and orientation of the thiophene and pyridine moieties of 2-(2'-thienyl)pyridine adsorbed to Au(111) in neutral and basic solution.
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http://dx.doi.org/10.1039/b208912bDOI Listing
December 2002
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