Surface Characterization of Gold Electrodes coated with - - PowerPoint PPT Presentation

Surface Characterization of Gold Electrodes coated with Photoreaction Centers

Progress Report (Chem 449) Sylvester Zhang

Bizzotto Group University of British Columbia

November 6, 2019

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Motivations

Binding and measurement of protein on electrode Langmuir isotherm to determine coverage characteristics of protein on Gold Evidence of electron tunneling via maximum photocurrent vs electrode separation

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Introduction

Photoreaction center extracted from bacterium membrane Redox active cofactors - chlorophyll-like molecules that absorb light and excite an electron When P (yellow molecule) absorbs light, and electron excited, electrons flow down this pathway

• 1. Rhodobacter sphaeroides photosynthetic bacteria.
• 2. Relevant protein: ”Reaction Center” or ”RC” 1

1Jones, M. R. The Petite Purple Photosynthetic Powerpack. Biochm. Soc. Trans. 2009, 37

(2), 400–407.

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Methods

Cyclic Voltametry Periodic excitation of reaction center Lock-in Method

• 1. Measure electrochemical current - background signal (mA) from electrode
• redox species in solution
• 2. Light excites photoreaction center periodically - generate small desired

signal (nA/pA) from reaction center to electrode transfer

• 3. Measure periodic increase and decrease in current - consider this

photocurrent2

2Jun, D.; Beatty, J. T.; Bizzotto, D. Highly Sensitive Method to Isolate Photocurrent Signals

from Large Background Redox Currents on Protein-Modified Electrodes. ChemElectroChem 2019, 6 (11), 2870–2875.

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Photocurrent Signal Origins

Excited electron donates to electrode Photoreaction center flexes when excited, resulting in a 13 Hz change in background signal

• 1. Source of detected currents may be from:

1.1 Electron transfer from protein to electrode 1.2 onformational flexing of reaction center changing effective concentration of mediators near electrode

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Identifying sources of signal

No light - control results in no photocurrent signal, and no locked in phase signal. Operation with light shows real signals occuring at 13 hz.

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Adsorption Characterization

Increasing coverage = increasing photocurrent, decreasing capacitance

Maximum photocurrent vs protein concentration (signal variations) Capacitance (F) vs concentration

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Future Directions

Reaction center molecules

• 1. Ensure that photocurrent observed is truly from excited protein
• 2. Explore possibility that electron transfer from protein is electron tunneling

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Acknowledgments

• Prof. Daniel Bizzotto
• Dept. Microbiology and Immunology
• Ms. Tianxiao Ma
• Prof. Thomas Beatty
• Mr. Adrian Grzebowsky
• Dr. Daniel Jun
• Ms. Jessica Shi
• Ms. Amita Mahej

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