Entrapment of Photosystem I within Self-Assembled Films

“Entrapment of Photosystem I within Self-Assembled Films”

Helen A. Kincaid, Tom Niedringhaus, Madalina Ciobanu, David E. Cliffel, and G. Kane Jennings

Purpose

This paper discusses the ability to extract photosystem proteins from plants and incorporate them into devices that take advantage of the light harvesting ability of the proteins to generate electricity.  It focuses on the method of forming a SAM on the surface of a gold substrate and using this SAM to attach photosystem I in a patterned structure.  Alkanethiol SAMs with chain lengths longer than 12 carbons were shown to be too long and prevented charge transfer to the Au substrate.

Methods

Gold substrates were prepared using a silicon wafer that was cleaned and coated with evaporated chromium and gold layers.  SAMs were formed on the Au surface by immersion of the substrate in a 1 mM alkanethiol and ethanol solution.  The same process was done in a solution of PSI to get a thin layer of PSI on the SAM.  After finishing this process, the SAMs were backfilled with a long-chain alkanethiol in different solvents depending on the experiment.  Reflectance-Absorbance Infrared Spectroscopy (RAIRS), Spectroscopic Ellipsometry (SE), and Electrochemical Impedance Spectroscopy (EIS) were used to do electrochemistry on the resulting SAM/PSI covered substrate.

Key Findings

Backfilling the SAM is found to be essential in controlling the coverage of the PSI on the substrate.  Also time of exposure and concentration of the PSI solution are found to affect the type of coverage that the PSI will have on the SAM.  The choice of solvent (polarity) is involved in the quality of the backfilled SAM that is formed.  Polar solvents are found to be more effective than nonpolar solvents in getting a densely packed SAM.