Sharon L. Neal, Associate Professor
University of Delaware
174 Brown Lab
Newark, DE 19716
(b. 1958) B.S., 1980, Spelman College; Ph.D., 1988, Emory University
The focus of our research is the development and application of spectroscopic instruments and measurements that isolate and monitor interactions between small solute molecules (dyes, toxins, drugs) and model membranes or other macrocyclic structures that are formed when amphiphilic molecules spontaneously self-assemble (organized media).We use multivariate optical spectroscopy to provide the enhanced selectivity required to monitor solutes as they encounter the heterogeneous microenvironments presented by organized media. We also use multivariate vibrational spectroscopy to study the formation and transitions of organized media. Multivariate measurements are acquired by varying more than one measurement parameter. For example, the figure below shows fluorescence data collected as a function of wavelength and time. The enhanced selectivity of multivariate measurements is best exploited by multivariate analysis (a subset of chemometrics), which uses applied mathematics to resolve spectral signals of complex samples. Other long-term goals of our work include photokinetic analysis of novel (or uncharacterized) multi-state probes, molecules that have spectral properties, e.g., absorption maxima, that are microenvironment sensitive and investigation of the unusual properties produced by molecular scale order in some organized media. For example, some mixed lipid aggregates solidify on heating.
Our recent work with PRODAN, a widely used polarity-sensitive multi-state probe, illustrates the utility of multivariate measurements and analysis. PRODAN is used to study biomembranes because the color of the dye changes with the state of the surrounding bilayer (fluid vs. solid). The emission maxima of conventional spectra shift steadily with increasing polarity of the solvent, but analysis of the multivariate fluorescence data we collected, see example below, revealed that even in pure solvents the PRODAN spectrum consists of more than one component. The effect was very dramatic in viscous alcohols, which means that in lipids each band of the spectrum should not automatically be interpreted as evidence that the probe being bound to membrane sites that differ in polarity.
In addition to work characterizing and applying multi-state probes and their associations with solvents and organized media, we use multivariate fluorescence or Raman spectroscopy to study a range of dynamic phenomena including structure changes in fluorescent proteins, interactions of cell-penetrating peptides with lipid membranes, and phase transitions of mixed lipid aggregates. For example, we coupled a fluorescence microscope to a multichannel detection system to construct a multivariate FCS (mvFCS) instrument that measures dynamic properties such as diffusion coefficients of multiple solutes in organized media.
- C.A. Roach and S.L. Neal "Numerical Correction of Detector Channel Cross-Talk Using Full-Spectrum Fluorescence Correlation Spectroscopy," Applied Spectroscopy, (2010) 64(10), 1145 – 1153.
- B. A. Rowe, C. A. Roach, J. Lin, V. Asiago, O. Dmitrenko and S. L. Neal “Spectral Heterogeneity of PRODAN Fluorescence in Isotropic Solvents Revealed by Multivariate Photokinetic Analysis,” Journal of Physical Chemistry A, (2008) 112(51), 13402 – 13412.
- B.A. Rowe and S.L. Neal “Photokinetic Analysis of PRODAN and LAURDAN in Large Unilamellar Vesicles Using Multivariate Frequency-Domain Fluorescence,”Journal of Physical Chemistry B, (2006) 110(30), 15021 – 15028.
- S. L. Neal and B. A. Rowe “Fluorescence Probe Study of Bicelle Structure vs. Temperature: Developing a Practical Bicelle Structure Model,” Langmuir, (2003) 19, 2039 – 2048.
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