Single-Molecule Spectroscopic Analysis of Mass Transport in Porous Metal Oxide Thin Films Using Fluorescent Nano-probes

The performance of porous, metal oxide, thin films in applications ranging from solid-state sensors to photovoltaic solar cells often depends critically on the mass transport of molecules through the tortuous channels that comprise the pore network of these films. Methods for the analysis of mass transport in such materials, therefore, play an important role in the development of film structures and morphologies optimized for specific applications. In this presentation, the use of a single-molecule spectroscopic technique, fluorescence correlation spectroscopy (FCS), is described in conjunction with the preparation and analysis of the diffusion of fluorescent nano-probes for the investigation of mass transport in porous metal oxide thin films. Measurements of nano-probe diffusion coefficients were obtained using a home-built FCS instrument. Florescent nano-probes used for the analysis were prepared by loading Nile Red into the hydrophobic cores of micelles prepared from diblock copolymers, C₁₈H₃₅-[CH₂CH₂O]₁₀ -OH (Brij S10) and C₁₈H₃₅-[CH₂CH₂O]₂₀ -OH (Brij S20). The fluorescence emission of Nile Red in the nano-probes exhibited a maximum peak at 620 nm, which enabled the FCS measurements. Fluorescence emission intensity autocorrelation functions for the nano-probes were modeled accurately by single exponential fits to the experimental data, indicating a narrow distribution of hydrodynamic diameters. Mean hydrodynamic diameters of 6.4 + 0.3 nm for Brij S10 and 8.8 + 0.2 nm for Brij S20 were in good agreement with diameter determinations obtained by other techniques. The small mean hydrodynamic diameters and the narrow size distribution of the nano-probes matched well the internal physical dimensions porous metal oxides films, which allowed kinetic determinations of the rate of nano-probe diffusion into the pores of the thin films.

About the Speaker

Dr. Remsen received his Bachelor of Science degree in Chemistry from Manhattan College, a Master of Science degree in Chemistry from the Polytechnic Institute of New York, and his Ph.D. in Chemistry from Princeton University. His doctoral dissertation research was performed in Professor Thomas Spiro's laboratory in the area of resonance Raman spectroscopy of mixed-valence compounds and electron transport proteins.

After receiving his doctorate, he joined Monsanto Plastics and Resins Co. as a Senior Chemist in the company’s Springfield, MA research facility. His area of research was the development of analytical techniques supporting the development of new polymer products that are transferred to Monsanto’s Corporate Research group in the company’s world headquarters St. Louis, MO. His research in Monsanto Corporate Research was the development of new analytical methods for supporting R&D and commercialization of new macromolecular products, including protein drugs. In 1992, he was appointed Monsanto Fellow in recognition of his work.

In 2000, he left Monsanto to take a Research Scientist position in the Department of Chemistry of Washington University in St. Louis. His research involved the analytical and physical chemistry of organic nanoparticles, which he performed in Professor Karen Wooley's laboratory.

In 2003, he joined Cabot Microelectronics Corporation in Aurora, IL, as a Senior Scientist and Manager and led the company’s Metrology Group in its Research and Development function.

In 2009, he took his present position as an Assistant Professor in the Mund-Lagowski Dept. of Chemistry and Biochemistry at Bradley University in Peoria, IL. He leads a research group of four undergraduate and three M.S. graduate researchers. His research areas include the study of mass transport in porous metal oxide thin films, adsorption behaviors on metal oxide nanoparticles, qualitative and quantitative analysis of biomarkers in fungi, and the characterization of protein-protein interactions in solution-producing protein fibrillation. He teaches the analytical chemistry sequence at Bradley, which includes Analytical Chemistry (CHM 326), Instrumental Analysis (CHM 420), and graduate-level analytical chemistry courses.