DNA film with light switching capabilities

Title: Preparation of [Ru(bpy)2(dppz)]2+-Intercalated DNA Cast Films Using a Self-Standing Method and Its Luminescence Tuning by Cu2+ Ions and EDTA

Journal: Inorganic Chemistry

Authors: Miojing Chen,* Hong Li,* Jiangyan Shao,* Yan Huang,* and Zheng Xu**

Affiliation: *Key Lab of Technology on Electrochemical Energy Storage and Power Generation in Guangdong Universities, School of Chemistry and Environment, South China Normal University, **Department of Chemical and Materials Engineering, University of Alberta

DNA is important to us as it codes our genetic material.  The properties of DNA and its interactions with other molecules are of extreme interest.   In order to better study DNA, “light switches” have been developed.  When bound to DNA, these compounds are extremely photoluminescent, but in their free form they exhibit little to no photoluminescence.  One compound that has been studied extensively as a DNA light switch is [Ru(bpy)2(dppz)]2+ (bpy = 2,2’-bipyridine; dppz = dipyrido-[3,2-a:2’,3’-c]phenazine].  [Ru(bpy)2(dppz)]2+ intercalates between DNA bases in order to form a photoluminescent compound.

[Ru(bpy)2(dppz)]2+

Previous studies focused on dilute solutions.  The authors point out that it is possible for DNA and luminescent materials to be in a condensed or solid state.  The measurements performed in the previous solution studies may not accurately represent the properties of DNA or luminescent materials when they are in these solid states.  To this end the authors describe the synthesis of a luminescent DNA film based on the intercalation of [Ru(bpy)2(dppz)]2+ into DNA.

After synthesizing the film, the authors studied the ability of Cu2+ to quench the photoluminescence.  The authors first studied this in solution.  Addition of a Cu2+ solution led to a 30% decrease in luminescence intensity.  Further studies indicated that in order to quench the luminescence, Cu2+ attaches to the [Ru(bpy)2(dppz)]2+ intercalated-DNA backbone via electrostatic attraction.  By introducing the chelating agent ethylenediaminetetraacetic acid (EDTA) most of the photoluminescence was recovered, because EDTA was able to bind the Cu2+ effectively removing it from the DNA.

The researchers then repeated this procedure on the newly synthesized film.  Similar results were achieved leading the authors to conclude that Cu2+ was able to interact with the intercalated DNA even when Cu2+ was in solution while the material was a solid.  They also concluded that EDTA was able to bind Cu2+ that was bound to the film.  Using specific quantities of Cu2+ and EDTA the researchers were able to control quenching and completely recover the photoluminescence.  This indicates that by alternating additions of Cu2+ and EDTA one would be able to repetitively switch luminescence on and off.

Schematic for the process to make a repetitive DNA light switch

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