Regional Meetings

95th Annual Technical Meeting of the Oklahoma Academy of Sciences
03 Nov 2006 (Friday), Rogers University, Claremore, OK
(meeting program)

Near-Infrared Fluorescence of the NBT/BCIP Chromogenic Stain and its Application to Fluorescence Microscopy.

Marshall D. McCutchen,¹ Le A. Trinh,² Marianne Bonner-Fraser,² Scott E. Fraser,² David W. McCauley,^2,3 and Lloyd A. Bumm¹

1) Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

2) Biology, The California Institute of Technology,1200 E. California Blvd., Pasadena, CA 91125, USA

3) Present address: Department of Zoology, The University of Oklahoma, 730 Van Vleet Oval, Norman, OK 73019, USA.

In situ hybridization techniques employing chromogenic staining by enzymatic amplification have been extensively employed to detect gene expression.  We demonstrate the previously unreported near infrared (NIR) fluorescence of the dark purple stain formed from 5-bromo-4-chloro-3-indolyl phosphate (BCIP) and nitro blue tetrazolium (NBT).  Although the product is a solid with strong optical absorption, its fluorescence enables high cellular resolution imaging of gene expression.  We have used spectrofluorometry in a fluorescence microscope to identify NBT diformazan as the component of the stain that is the fluorophore exhibiting the strong fluorescence signal.  The fluorescence shows an intense emission signal (780-910 nm) that is well separated from excitation (645-685 nm).  Fluorescence techniques when combined with optical sectioning can be used to construct 3-dimensional images but often have the disadvantage of a low signal to noise ratio and signal instability once the staining is completed.  The NBT diformazan fluorescence is also extremely photostable.  Using the highest intensity illumination we could apply, the half life of the stain for photobleaching was 27 min.  Because NBT/BCIP is a widely used chromogenic stain, existing staining protocols can also be applied to fluorescence imaging techniques to increase the resolution of gene expression patterns.

Oklahoma Research Day
06 Apr 2007 (Friday 7:30-14:00), University of Central Oklahoma, Edmond, OK
[originally scheduled 01 Dec 2006 (Friday 7:30-14:00)]

06.07.33

SEM-Correlated Single-Nanoparticle Spectroscopy

D.J. Wasielewski, M.D. McCutchen, E.S. Day, J.X. Wang, C.E. Allen, W.D. Tennyson, D.H. Dahanayaka, L.A. Bumm

Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

The surface plasmons, or oscillations of free electrons, of metal nanoparticles are strongly influenced by particle size and shape. Spectroscopy is commonly used to characterize nanoparticle samples, but typical absorption spectra only represent ensemble averages. Due to the polydispersity of the nanoparticle sols, much information is lost in traditional spectra.

Here we present a method to investigate the optical properties of individual nanoparticles. Flat gold nanoparticles are deposited on a microscope slide and observed under a dark-field microscope. Scattered light from an isolated nanoparticle is collected via an optical fiber and channeled into a spectrometer. Because many of the particles are too small to be clearly resolved in the optical microscope, the same nanoparticle is then imaged using high-resolution scanning electron microscopy to correlate its spectrum with its exact shape and size. SEM correlated spectra have revealed trends in shape-dependence of nanoparticle spectra. We present our experimental results and compare the theoretical prediction.

 

06.07.39

Ellipsoidal Mirrors for Light Collection

D. W. Kelle, D. J. Wasielewski, L. A. Bumm

Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

We are developing a light collection system for a scanning tunneling microscope (STM). The STM tunneling junction acts as an optical point source. An ellipsoidal mirror will collect and refocus the emitted light onto a photodiode. This task would be simple if imaging-quality ellipsoidal mirrors were available. Electroformed ellipsoidal mirrors are available at low cost, but their optical aberrations will spread the image of our point source. It is critical that we know the fraction of the emitted light that our detector is capable of collecting.

We have designed an optical test system to characterize the efficiency of the mirror. The sample is simulated by a tube-etched optical fiber tip. The percentage of light focused within the detector area is dependent upon the dimensions of the fiber tip’s source region. In order to normalize the efficiency, the dimension of the tip must be measured and taken into account. Minimizing this dimension will allow a more accurate result.

 

06.07.32

Flat Gold Nanoparticle Growth and Sedimentation

Christopher E. Allen, Wesley D. Tennyson, Daminda H. Dahanayaka, Lloyd A. Bumm

Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

Flat Gold Nanoparticles can serve as an atomically flat and optically resonant workbench for a variety of applications. These nanoparticles are grown in solution, which produces a wide variety of sizes and shapes ranging from triangles to hexagons. At the same time a large population of unwanted spherical gold nanoparticles also grow. My research has focused on size and shape fractionation of the as-grown sol using centrifugal sedimentation. I will also discuss other methods to improve the flat-to-sphere shape ratio using seeded nanoparticle growth and selective deposition of flat particles onto a variety of substrates. Dark-field optical microscopy and scanning electron microscopy are used for to evaluate our results.

 

06.07.31

A Study of Ligand Exchange Kinetics of Aluminum and Gallium Tris 8-Hydroxyquinoline Complexes

Daniel R. White,¹ Susan S. Alguindigue,² Lloyd A. Bumm¹

1) Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

2) Department of Chemistry and Biochemistry, The University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA.

Aluminum tris-(8-hydroxyquinoline) (Alq3) and its gallium analog are organic semiconductors which are widely used in organic LEDs. These and other molecules are the object of our group's single molecule electroluminescence studies. The color of their luminescence can be changed by substituting one or more of the 8-hydroxyquinoline ligands with modified luminescent spectra. Interestingly mixed ligand complexes are poorly characterized because the ligands can exchange with free ligands in solution. In addition, the complex adopts the meridional isomer where the 3 ligands surrounding the aluminum and the gallium ions are symmetry inequivalent. Performing our single molecule experiments requires an understanding of both the intramolecular and the intermolecular ligand exchange kinetics.

We are using nuclear magnetic resonance (NMR) spectroscopy to study the kinetics of this system. The intermolecular processes are measured from the time evolution of the NMR spectra after adding labeled free ligands. The temperature dependence of the kinetics is used to measure the thermodynamics of the exchange processes. This knowledge will allow us to develop an effective strategy for preparing and studying mixed ligand analogs of these technologically important materials.

 

96th Annual Technical Meeting of the Oklahoma Academy of Sciences
02 Nov 2006 (Friday), Tulsa Community College -- Southeast Campus, Tulsa, OK
(meeting program)

Single Flat Gold Nanoparticle Microscopy & Spectroscopy: A Study of the Effect of Nanoparticle Treatment.

W.D. Tennyson, C.E. Allen, D.S. Hartnett, M.D. McCutchen, D.H. Dahanayaka, L.A. Bumm

Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W Brooks St., Norman, OK 73019, USA.

We have investigated single flat gold nanoparticles (FGNPs) on a variety of platforms. We have explored absorptions of dyes (malachite green), surface cleaning, thermal annealing, and nanomechanical manipulation of the FGNPs. We can directly measure the effect of the treatments to an individual nanoparticle by correlating the before-and-after spectra with before-and-after microscopy (AFM and SEM). Finding the same nanoparticle again and again can be a significant barrier in correlation, however we have developed a photolithograpically- prepared addressed-grid system to assist finding the particles in multiple measurement platforms. This method also allows facile correlation of the light-scattering spectra to size, shape, thickness, and local environment.

63rd Southwestern Regional Meeting of the ACS (SRWM07)
04-07 Nov 2007, Lubbock, TX
(meeting program)