Dale Willard - Academia.edu (original) (raw)

Papers by Dale Willard

We report on solvation dynamics at lecithin interfaces in two different reverse micellar systems ... more We report on solvation dynamics at lecithin interfaces in two different reverse micellar systems and at the interface in small unilamellar vesicles. In the reverse micelles, the morphology dramatically affects the observed solvation dynamics as the solvent is significantly more immobilized in tubular than in spherical reverse micelles. This is interpreted as evidence for water pool formation in the spherical micelles and supports the hypothesis of substantial headgroup-water interactions in the tubular micelles. In vesicular studies, we compare and contrast results from vesicles with previous measurements in reverse micelles. Additionally, we probe the effect that cholesterol has on the water mobility at the vesicular interface.

Springer Series in Chemical Physics, 1998

Laser Techniques for Surface Science II, 1995

ABSTRACT We have measured the absorption spectrum of the laser dye IR125 (also known as indocyani... more ABSTRACT We have measured the absorption spectrum of the laser dye IR125 (also known as indocyanine green) at the water/air interface using resonant enhanced surface second harmonic generation. The spectra of the dye molecules at the interface are extremely sensitive to the bulk concentration. All the surface spectra reflect aggregation of the dye at the interface, even at the smallest concentrations detectable, below 1 (mu) M. Resonant enhanced second harmonic generation appears to be a good technique for measuring spectra at liquid interfaces.

Environmental science and pollution research international, 2003

This article is a review of new and versatile optical-immunoassay instrumentation for water monit... more This article is a review of new and versatile optical-immunoassay instrumentation for water monitoring developed through two European Union projects, RIver ANAlyser (RIANA) and Automated Water Analyser Computer Supported System (AWACSS). Both projects utilise immunoassay techniques to isolate the analytes and Total Internal Reflection Fluorescence (TIRF) to quantify them. Completed in 1999, the RIANA project developed a sensitive and cost-effective analytical system capable of simultaneous detection of multiple-analytes in real-world water samples. The AWACSS project has been in progress since 2001 and is developing rugged-but-sensitive instrumentation that will detect up to 30 analytes simultaneously, will operate unattended, and will have networking capability.

globalhub.org

ABSTRACT: Advanced MicroLabs (AML) received a Phase II SBIR award allowing them to develop a micr... more ABSTRACT: Advanced MicroLabs (AML) received a Phase II SBIR award allowing them to develop a microfluidic-based disposable microchip for the determination of Glycated Hemoglobin concentrations in whole blood. For the product to be marketable, sample ...

The Journal of Physical Chemistry B, 1998

... 70 attributed the slower dynamics to the dipolar nature of the probe molecules. They base thi... more ... 70 attributed the slower dynamics to the dipolar nature of the probe molecules. They base this result on recent computer simulations performed by Nandi et al. ... However, Nandi et al. 71 calculated a tcf for bulk water that agrees well with that reported by Jimenez et al. ...

The Journal of Physical Chemistry B, 2000

... 2) Maitra, A.; Jain, TK; Shervani, Z. Colloid Surf.1990, 47, 255−67. ...

Review of Scientific Instruments, 1997

We have used a white light continuum generated with ultrashort laser pulses from a Ti:sapphire la... more We have used a white light continuum generated with ultrashort laser pulses from a Ti:sapphire laser system as the radiation source for second-harmonic generation measurements. The white light continuum provides easily tuned radiation for experiments requiring a range of wavelengths. Despite the small coherence length of the radiation, parametric processes, such as second-harmonic generation, are possible with this source. In particular, surface second-harmonic generation using the white light continuum is reasonable because the extent of the interface is much smaller than the coherence length of the radiation. We demonstrate second-harmonic generation from a gold surface and show that surface second-harmonic generation using the white light continuum can be used to measure absorption spectroscopy of molecules adsorbed to surfaces via resonance enhancement of the surface second-harmonic signals.

Journal of the American Chemical Society, 1998

ABSTRACT The solvation dynamics of water in lecithin/cyclohexane reverse micelles have been deter... more ABSTRACT The solvation dynamics of water in lecithin/cyclohexane reverse micelles have been determined via ultrafast time-resolved fluorescence studies. At hydration levels w0 ≤ 4.8, the reverse micellar samples are nonviscous. Here a single relaxation time is observed that is much longer than the response of free or bulk water. In contrast, small additions of water to the samples produces a viscous gel, referred to by others as an organogel or “living polymer”. At hydration levels of w0 ≥ 5.8, three relaxation times are observed with approximate time constants of 0.5, 15, and 200 ps, the shortest of which correlates to free water motion. The dynamics reveal no evidence of micelle crossover or branch points associated with gel formation. In comparison to Aerosol OT reverse micelles of similar hydration, the water in the lecithin reverse micelles is significantly more restricted. It is proposed that lecithin sequesters significantly more water than previously predicted precluding formation of distinct core water pools in the micelles. The results are also compared to models for aqueous structure and dynamics near phospholipid membranes and to bulk water dynamics.

Journal of the American Chemical Society, 2005

Many emerging fields of science and technology rely on precise patterning of functional molecules... more Many emerging fields of science and technology rely on precise patterning of functional molecules on surfaces. Examples include the creation of DNA and protein microarrays and other bioanalytical sensors, the formation of functional biomaterial interfaces, and the creation of molecular-scale electronics devices. A variety of patterning techniques exist that allow the patterning of substrates on the micrometer to nanometer scale, including scanning tunneling microscopy (STM), 1 dip-pen nanolithography (DPN), 2-4 micro-contact printing (μCP), 5,6 photolithography, 7,8 nanopipet, 9 etc. However, patterns of arbitrary complexity remain a difficult problem. For example, the need to create patterns containing multiple components, small patterns separated by large distances, or large patterns next to small patterns motivates us to develop more versatile patterning capabilities. In this paper, we demonstrate an alternative patterning technique, which we refer to as single feature inking and stamping (SFINKS). Notably, SFINKS can pattern multiple components with complex structures and without crosscontamination.

Organic Mass Spectrometry, 1993

H-D exchange reactions of methanol-d, with protonated amino acids were performed in an external-s... more H-D exchange reactions of methanol-d, with protonated amino acids were performed in an external-source Fourier transform mass spectrometer. Absolute rate constants were determined for the group which included glycine, alanine, valine, leucine, isoleucine and proline. By comparing reactivities with selected methyl esters, it was found that exchange on the carboxylic acid occurs 3-10 times faster than exchange on the amino group. No simple correlation is observed between the rates of H-D exchange on the acid group and the size of the alkyl group. However, the rates of exchange on the amine decrease with increasing gas-phase basicity. Glycine, the least basic amino acid, exchanges its amine hydrogens the fastest. These results are useful for determining the interaction of methanol with protonated amino acids and can provide insight into the H-D exchange reactions observed with polyprotonated proteins produced by electrospray ionization.

Environmental Science and Pollution Research, 2003

Biosensors and Bioelectronics, 2005

A novel analytical system AWACSS (automated water analyser computer-supported system) based on im... more A novel analytical system AWACSS (automated water analyser computer-supported system) based on immunochemical technology has been developed that can measure several organic pollutants at low nanogram per litre level in a single few-minutes analysis without any prior sample pre-concentration nor pre-treatment steps.

Analytical Chemistry, 2001

Individual fluorescent polystyrene nanospheres (<10-100-nm diameter) and individual fluore... more Individual fluorescent polystyrene nanospheres (<10-100-nm diameter) and individual fluorescently labeled DNA molecules were dispersed on mica and analyzed using time-resolved fluorescence spectroscopy and atomic force microscopy (AFM). Spatial correlation of the fluorescence and AFM measurements was accomplished by (1) positioning a single fluorescent particle into the near diffraction-limited confocal excitation region of the optical microscope, (2) recording the time-resolved fluorescence emission, and (3) measuring the intensity of the excitation laser light scattered from the apex of an AFM probe tip and the AFM topography as a function of the lateral position of the tip relative to the sample substrate. The latter measurements resulted in concurrent high-resolution (approximately 10-20 nm laterally) images of the laser excitation profile of the confocal microscope and the topography of the sample. Superposition of these optical and topographical images enabled unambiguous identification of the sample topography residing within the excitation region of the optical microscope, facilitating the identification and structural characterization of the nanoparticle(s) or biomolecule(s) responsible for the fluorescence signal observed in step 2. These measurements also provided the lateral position of the particles relative to the laser excitation profile and the surrounding topography with nanometer-scale precision and the relationship between the spectroscopic and structural properties of the particles. Extension of these methods to the study of other types of nanostructured materials is discussed.

Analytical and Bioanalytical Chemistry, 2006

Nanoscale sensors can be created when an expected energetic pathway is created and then that path... more Nanoscale sensors can be created when an expected energetic pathway is created and then that pathway is either initiated or disrupted by a specific binding event. Constructing the sensor on the nanoscale could lead to greater sensitivity and lower limits of detection. To this end, quantum dots (QDs) can be considered prime candidates for the active components. Relative to organic chromophores, QDs have tunable spectral properties, show less susceptibility to photobleaching, have similar brightness, and have been shown to display electro-optical properties. In this review, we discuss recent articles that incorporate QDs into directed energy flow systems, some with the goal of building new and more powerful sensors and others that could lead to more powerful sensors.

Analytica Chimica Acta, 1995

The decomposition of oligosaccharide anions is investigated using the low energy collisional acti... more The decomposition of oligosaccharide anions is investigated using the low energy collisional activation and Fourier transform mass spectrometry. The dissociation of the anion, specifically the monosaccharide rings, provides information on the types of linkage that form the glycosidic bonds. The fragment ions observed under liquid secondary ion mass spectrometry ionization and low energy collisional activation conditions show that the deprotonation of the anomeric position is necessary for cleaving the saccharide ring. For this reason, fragmentation occurs readily on the reducing end of the molecule. When the reducing ring is derivatized, or linked so that deprotonation of the anomeric ring is not possible, cross-ring fragmentation is not observed. A mechanism for cross ring cleavage is proposed based on experimental results. Molecular orbital calculations are performed to predict the activation barrier of each step and the overall dissociation process.

Nano Letters, 2001

Specific binding of biotinilated bovine serum albumin (bBSA) and tetramethylrhodamine-labeled str... more Specific binding of biotinilated bovine serum albumin (bBSA) and tetramethylrhodamine-labeled streptavidin (SAv−TMR) was observed by conjugating bBSA to CdSe−ZnS core−shell quantum dots (QDs) and observing enhanced TMR fluorescence caused by fluorescence resonance energy transfer (FRET) from the QD donors to the TMR acceptors. Because of the broad absorption spectrum of the QDs, efficient donor excitation could occur at a wavelength that was well resolved from the absorption spectrum of the acceptor, thereby minimizing direct acceptor excitation. Appreciable overlap of the donor emission and acceptor absorption spectra was achieved by size-tuning the QD emission spectrum into resonance with the acceptor absorption spectrum, and cross-talk between the donor and acceptor emission was minimized because of the narrow, symmetrically shaped QD emission spectrum. Evidence for an additional, nonspecific QD−TMR energy transfer mechanism that caused quenching of the QD emission without a corresponding TMR fluorescence enhancement was also observed.