University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Langmuir

  • Publisher: American Chemical Society
  • FAD Code: LANG
  • CODEN: LANGD5
  • ISSN: 0743-7463
  • Abbreviation: Langmuir
  • DOI Prefix: 10.1021/la
  • Language: English
  • Comments: Fulltext from 1985 V1

Citations 8

"On-Line Monitoring Of Polymer Deposition For Tailoring The Waveguide Characteristics Of Love-Wave Biosensors"
Langmuir 2004 Volume 20, Issue 6 Pages 2315-2319
Florian Bender, Kerstin Länge, Nicole Barié, Jun Kondoh and Michael Rapp

Abstract: The Love-wave sensor is an acoustic sensing device which is particularly suitable for sensing in a liquid environment. The superior characteristics of the device are achieved by the use of an acoustic waveguide, consisting of a thin layer deposited on the surface of the substrate material. The exact thickness and material properties of the layer will not only determine sensitivity and sensing performance of the resulting device but can also be adjusted to generate higher-order Love modes. Thus, to obtain a sensing device with the desired specifications, precise control over the process of waveguide deposition is required. This has been realized by implementation of a vapor deposition polymerization system where the transmission curve (amplitude vs frequency) of one of the sensing devices is continuously monitored during deposition. As soon as the desired device specifications are reached, the deposition can be interrupted immediately. From the recorded transmission curves, information about the sensitivity of the device can be deduced, and the formation of higher-order Love modes can be visualized. The system has been used to produce biosensors based on various Love modes. It is shown that sensors operated on higher-order Love modes have a high mass sensitivity which, together with their excellent shielding properties, makes them advantageous for biosensing in conducting buffer solutions.

"Surface Plasmon Resonance Studies On The Electrochemical Doping/dedoping Processes Of Anions On Polyaniline-modified Electrode"
Langmuir 2002 Volume 18, Issue 26 Pages 10305-10310
Xiaofeng Kang, Yongdong Jin, Guangjin Cheng, and Shaojun Dong

Abstract: The combination of in situ surface plasmon resonance (SPR) with electrochemistry was used to investigate the electrochemical doping/dedoping processes of anions on a polyaniline (PAn)-modified electrode. Electrochemical SPR characteristics of the PAn film before and after doping/dedoping were revealed. The redox transformation between the insulating leucoemeraldine, and the conductive emeraldine, corresponding to the doping/dedoping of anion, can lead to very distinct changes in both the resonance minimum angle and the shape of SPR curve. This is ascribed to the swelling/shrinking effect, and the change of the PAn film in the imaginary part of the dielectric constant resulted from the transition of the film conductivity. In situ recording the time evolution of reflectance change at a fixed angle permits the continuous monitoring of the kinetic processes of doping/dedoping anions. The size and the charge of anions, the film thickness, as well as the concentration of anions are shown to strongly influence the rate of ingress/egress of anions. The time differential of SPR kinetic curves can be well applied in the detecting electroinactive anion by flow injection analysis. The approach has higher sensitivity and reproducibility compared with other kinetic measurements, such as those obtained by amperometry.

"Simple Method For Preparing Controllably Aggregated Silver Particle Films Used As Surface-enhanced Raman Scattering Active Substrates"
Langmuir 2002 Volume 18, Issue 18 Pages 6839-6844
Jiawen Hu, Bing Zhao, Weiqing Xu, Yuguo Fan, Bofu Li, and Yukihiro Ozaki

Abstract: Silver colloids Are, one of the extensively employed surface-enhanced Raman scattering (SERS) active substrates. To obtain the SERS effect, their aggregation upon addition of analyte is necessary. However, problems of instability and irreproducibility in the magnitude of the signal are caused by the formation of aggregates. Considering that the aggregation of silver colloids is essential to induce small silver clusters, in the present study, we develop a drying process to prepare silver particle films (silver clusters) that are supported directly on a glass slide. These silver particle films arise through the aggregation of silver colloids occurring in thin water films supported on a solid substrate. With the evaporation of water, silver clusters are left on the solid substrate. Thus, the assembly meets perfectly the requirement of aggregation of silver colloids and, at the same time, possesses the stability of solidlike SERS-active substrates. We can easily obtain excellent SERS spectra from these silver particle films. These substrates show great potential in practical applications such as ultrasensitive microanalysis with micro-Raman spectroscopy and are suitable for studying the optical properties of silver clusters. 4-Mereaptopyridine (4MPY) was used to test the utility of the proposed method and to compare it with the chemically deposited silver film (silver mirror) method. The intensity of SERS signals of 4MPY on the silver particle films is stronger by about 100 times than that of 4MPY on the silver mirror. In addition, the experimental results of SERS reveal that the activation agent, coadsorbed chloride ions, can further enhance the SERS, signals from both the silver mirror and the silver colloids.

"Disjoining Pressure Vs Thickness Isotherms Of Thin Emulsion Films Stabilized By Proteins"
Langmuir 2001 Volume 17, Issue 26 Pages 8069-8077
Tatiana D. Dimitrova, Fernando Leal-Calderon, Theodor D. Gurkov, and Bruce Campbell

Abstract: In the present paper, we report measurements of the disjoining pressure vs thickness isotherms of emulsion films stabilized by proteins. A novel variant of the Mysels-Bergeron thin liquid film setup was constructed and further employed in the investigation of foam and emulsions films. The films are formed in a porous glass plate immersed in the corresponding oil phase. The disjoining pressure is directly measured by means of a pressure transducer, and the thickness is determined via light interferometry. The disjoining pressure vs thickness isotherms show different features in respect to the stabilizing protein. When the films are stabilized by bovine serum albumin (BSA) and beta -lactoglobulin (BLG), a steric-like interaction comes into play being differently pronounced in the two cases. In contrast, the films stabilized with beta -casein exhibit classical Derjaguin-Landau-Verwey-Overbeek (DLVO) behavior. The disjoining pressure was converted to force adopting the Derjaguin approximation, and the result is compared with force-distance laws obtained employing magnetic chaining technique (MCT); there is an excellent agreement. Similar comparison with data obtained in a surface force apparatus (SFA) experiment reveals substantial discrepancies due to the different physical state of the proteins adsorbed at a liquid-liquid and a solid interface. The experiment reported here demonstrates one important possibility for realistic modeling of the interaction between emulsion droplets.
Adsorption

"Surface Structure And Coverage Of An Oligonucleotide Probe Tethered Onto A Gold Substrate And Its Hybridization Efficiency For A Polynucleotide Target"
Langmuir 2001 Volume 17, Issue 4 Pages 1215-1224
Eva Huang, Munlika Satjapipat, Shubo Han, and Feimeng Zhou

Abstract: A single-stranded oligonucleotide whose 5 end is derivatized with a mercaptohexyl tether group was either directly anchored onto a gold surface or attached to a gold surface as part of a mixed self-assembled monolayer that contains mercaptohexanol. The application of these surface-confined DNA oligomers as heterogeneous probes for the detection of polynucleotides (e.g., M13 phage DNA) is considered, with an emphasis on the elucidation of the relationship between the hybridization efficiency and the surface coverage and orientation of the probe molecules. Atomic force microscopy (AFM) and flow injection quartz crystal microbalance (FI-QCM) were used in tandem to study the immobilization of the probe, to estimate the extent and efficiency of the hybridization of M13 phage DNA (7249 bases), and to examine the effect of using a different alkanethiol to reorient the preformed film for a higher hybridization efficiency. The surface density and the resultant hybridization efficiency were found to be highly dependent on the morphology and surface structure of the gold substrate as well as on the concentration of the solution used for the probe fabrication but much less dependent on the probe immobilization time. The lower limit of the hybridization efficiency was estimated to be about 1.1% which is an underestimate because only the resolvable circular features were included in the estimation. Although the duplex formed at the gold surface covered with only the thiolated DNA probe adopts exclusively the orientation in which the target loop is parallel with respect to the substrate surface, the predominant duplex orientation at the gold substrate modified with mixed self-assembled monolayers is tethered to the surface with a small tilt angle versus the surface normal. Visualization of the duplex orientation allows one to understand whether the Sauerbrey equation is valid for the interpretation of certain FI-QCM results. Although it is probably valid to use the Sauerbrey equation to calculate the amount of a polynucleotide at a surface covered only by the thiolated DNA probe, the practice might be questionable for that at the surface with the DNA/alkanethiol mixed SAM on the basis of our AFM images of the target orientations.

"Probing The Barrier Properties Of Self-Assembled Monolayers Using Flow Amperometry"
Langmuir 1999 Volume 15, Issue 5 Pages 1884-1886
Joseph Wang, Jose Luis Lopez Paz, and Mian Jiang

Abstract: The application of flow injection amperometry for elucidating the barrier properties of self-assembled monolayer-coated gold electrodes is demonstrated. The remarkable sensitivity of such flow injection experiments permits convenient and quant. assessment of the barrier behavior over a wide range of packing densities. Flow-amperometry can thus be added to the other tools which are used to characterize monolayer assemblies and to evaluate modified-electrode systems.

"Interfacial Properties Of Biotin Conjugate-avidin Complexes Studied By Acoustic Wave Sensor"
Langmuir 1999 Volume 15, Issue 2 Pages 564-572
Shakour Ghafouri and Michael Thompson

Abstract: The adsorption of avidin, neutravidin, and biotin-labeled dextran 10,000, dextran 70,000, bovine albumin, and insulin to the gold electrodes of thickness-shear-mode acoustic wave devices was studied in a flow injection analysis configuration. Electrodes with different surface rugosity and free energy were also examined Changes in series resonance frequency for the various molecules as a result of electrode adsorption cannot be explained in terms of the conventional mass-response effect. Perturbation of the properties of the protein and polysaccharide layers, such as their viscosity, and acoustic coupling phenomena offer a more reasonable basis to evaluate the results. In an analogous fashion, the acoustic wave sensor signals obtained for the formation of the various avidin-and neutravidin-biotin conjugate samples do not correspond to the additional mass deposited on the device surface. The responses for the binding of biotinylated insulin to avidin and to the nonglycosylated form of the parent mol. were completely different. This result is ascribed to a difference of surface free energy associated with the two protein-based interfaces. The acoustic wave sensor was also employed to investigate the formation of avidin-biotin conjugate multilayer structures on the surface of the device. Multilayer buildup is detectable for several pairs of avidin-biotin interactions, but the corresponding shifts in series resonance frequency gradually diminish in magnitude. Finally, the introduction of biotin itself appears to result in structural changes in the multilayer deposit, causing alterations in viscoelastic properties.
Adsorption

"Determination Of Binding Constants By Flow Injection Gradient Technique"
Langmuir 1998 Volume 14, Issue 24 Pages 6886-6892
Chieu D. Tran, Mauricio S. Baptista, and Takuya Tomooka

Abstract: A new method based on the flow injection gradient equipped with an acoustooptic tunable filter (AOTF) detector has been developed for the determination of binding constants of substrates with cyclodextrins or micelles. The concentration. gradient produced by this method eliminates the need to prep. series of mixtures in which the concentrations. of one of the reactants are varied. The fast scanning ability of the AOTF enables the detector to record the whole absorption spectrum of the mixture as it flows through the flow cell. Binding constants can be rapidly determined The effectiveness of the method was evaluated by determining binding constants of inclusion complex formation between β-cyclodextrin (β-CD) and phenolphthalein and of the incorporation of organic molecules (e.g., p-toluenesulfonic acid (PTS) and benzophenone (BP)) into micelles (CTAB) under steady state condition (no flow) and compared with values determined under the flow injection gradient. The method is particularly effective for charged substrates, e.g., the binding constants obtained between PTS and CTAB and between phenolphthalein and β-CD. Neutral substrate, BP, gives relatively poor accuracy and reproducibility, and these may be due to the adsorption of the substrate onto the flow device.
Binding constants Benzophenone p-Toluenesulfonic acid Phenolphthalein Spectrophotometry Complexation Gradient technique Acousto optic tunable filter