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.

Electrochemistry and photoelectrochemistry of photosystem I adsorbed on hydroxyl-terminated monolayers

Purpose of this article:

PSI photovoltaic devices have been made using a SAM supported PSI monolayer, and this article shows the electrochemistry done on these devices to show the ability to absorb light and transfer the energy into current.

Methods used in this article:

Dark experiments:

1. Controls were made that showed the activity of a SAM covered gold substrate, and they were tested with cyclic voltammetry (CV) and square wave voltammetry (SWV) under dark conditions.
2. PSI was then added to these SAMs to show the difference in activity using the same CV and SWV methods.

Light experiments

1. Chronoamperometry was done on PSI covered electrodes.
2. Chronoamperometry was done on electrodes that were submerged in the same buffer solution without PSI as controls.

Conclusions:

Photovoltaic devices using SAM-modified gold substrates can be made with PSI that continues to be photoactive even after being attached to the SAM.  The close packed SAM and PSI monolayer reduces the gold peak enough to show the activity of the PSI alone, and a SAM as long as 8 carbons can be used to get this result.

Electrospun nanofiber scaffolds: engineering soft tissues

Shawn Rosson

“Electrospun nanofiber scaffolds: engineering soft tissues”

 

Purpose:  This article was written explaining the process of electrospinning.  It covers the process of electrospinning, usefulness of the process, and the variables that can be changed to modify nanofiber size, structure, etc.  Nanofibers can be used in many applications, some including uses as scaffolds in tissue engineering, filtration, barrier fabrics, wipes, personal care items, etc.

 

Methods/procedures: A solution is made with a concentration depending on the intended structure of the nanofibers.  Concentration is important in size and thickness of the nanofibers, and also if the concentration is low enough, the fibers will have “beads” on the fibers.  Once this solution is made with the desired concentration, it is ejected through a syringe with an applied potential of a few kV.  The jet that is ejected rapidly travels to the collector.  The collector can take the form of many things, which can be varied depending on the desired fiber structure.  It can be wound around a cylindrically shaped bar to make a tubular nanofiber scaffold, it can be woven in a matrix of fibers, or it can be made into straight parallel fibers. 

 

Key findings: Variables that can be changed such as polymer molecular weight, solution properties, applied electric potential, polymer solution flow rate, distance between spinneret and collector, motion of the grounded target and ambient parameters.  These variables control the size and structure of the resulting nanofibers.  Studies were done on the concentration of the polymers and the nanofibers produced by those varying concentrations.  What was found is that higher concentrations produced thicker diameter nanofibers and lower concentrations could begin to become “beaded” below a certain concentration.  Also, fiber alignment was varied by changing the collectors.  Some collectors were rotated to make a hollow tube-like structure, while others remained flat and different potentials were applied to make the fibers stay straight and parallel to each other.

Nanomaterial-Based Electrochemical Biosensors for Medical Applications

Shawn Rosson

Nanoscale Sci and Eng

9/14/08

 

Nanomaterial-Based Electrochemical Biosensors for Medical Applications

Kagan Kerman, Masato Saito, Shohei Yamamura, Yuzuru Takamura, Eiichi Tamiya

 

According to this article, nanotechnology is used in many different biosensing applications.  Studies were done on the metal nanoparticles used in electrochemical biosensors, the catalysts used in biosensors, methods of detecting nucleic acids and proteins, and carbon nanotube transistor based biosensors.  Each of these uses a property of nanoscale material that is beneficial to the medical field. 

Metal nanoparticles, such as gold, have been found to have many uses.  The properties of the material are greatly determined by the size and shape of the molecule, as opposed to larger scale molecules that have consistent properties depending mostly on the composition.  The process of vapour deposition is used to make nanoparticles out of larger bulk materials.  This method is used to coat substrates with very thin layers of the desired metal.  This is a physical method of forming nanoparticles from bulk materials, but other chemical methods such as reduction of ionic metal atoms to individual metal atoms are also available.  Also SAMs take advantage of the strong attraction of gold to thiol groups in order to make stable single-layered structures of a desired alkanethiol.

            Metal nanoparticles are also taken advantage of in the catalytic process.  Studies have been done using metal nanoparticles as a catalyst in biosensors.  The advantage of using metal nanoparticles rather than traditional catalysts is the full regeneration of the metal after the reaction has been completed.  Because of the strong binding of thiol groups to gold particles, the biosensors using these gold nanoparticles would be able to sense thiol containing neurotoxins.  Several other Au based biosensors were developed using the properties of the Au nanoparticles. 

            Biosensors have also been made to detect single-nucleotide polymorphisms using Au nanoparticles to provide an electrochemical signal when binding occurs between the Au and the short-DNA oligonucleotides. Using this method rather than conventional processes, the detection should be cheaper, faster, and more sensitive.  This method was further improved using quantum dots (QDs) to determine the code of the SNP in a shorter time. Similar methods are also used for protein sensing.  The antigen (protein) binds to the antibody, which produces an electrochemical signal for detection.

            All of these methods are used in the area of biosensing using nanomaterials.  There have been multiple applications for Au nanoparticles discussed in this article, including uses as catalysts, binding sites for thiol groups for protein and nucleotide detection, and to make SAMs for use in many fields.