Nitroxides as Fluorescence Quenchers

The synthesis and applications of profluorescent nitroxides is the newest endeavor in our labs, recently becoming a major focus. Profluorescent nitroxides quench fluorescence of closely tethered fluorophores:

Nitroxides + “Quantum Dots”

Using our thiol or disulfide functionalized alkoxyamines, we have been collaborating with our UCSC colleagues Prof. Jin Zhang and Prof. Shaowei Chen in anchoring our initiators onto CdSe and Ag nanoparticles. An obvious extension is the exploration of the ability of nitroxides to quench highly fluorescent CdSe nanoparticles (also known as “quantum dots”). We are exploring the ability of carboxylates and amines to act as effective ligands to bind to the CdSe surface. By fluorescence, we have found that 4-amino-TEMPO (also explored by the Scaiano group) is the most effective quencher.  By EPR (in collaboration with Prof. Glenn Millhauser  here at UCSC), we have found that the bidentate bisamine shows the tightest binding to the CdSe nanoparticles. We have demonstrated restoration of fluorescence upon trapping the nitroxide moiety with ethyl radical to form alkoxyamine: C. Tansakul, E. Lilie, E. D. Walter, F. Rivera III, A. Wolcott, J. Z. Zhang, G. L. Millhauser, R. Braslau* “Distance-dependent Fluorescence Quenching and Binding of CdSe Quantum Dots by Functionalized Nitroxide Radicals,” J. Phys. Chem. C, 2010, 114, 7793-7805.

fluorescence is restored upon reaction of the nitroxide, typically to from the alkoxyamine or hydroxylamine.  Profluorescent nitroxides have been studied for about 20 years by a number of research groups.  

Detection of Urushiol from Poison Oak/Ivy/Sumac with Profluorescent Nitroxides

Contact with poison oak, poison ivy or poison sumac elicits contact dermatitis in about 70% of the population.  Avoidance of the invisible oil is the best way to prevent the annoying and in some cases medically incapacitating immunoresponse.   The Braslau group is working on a method to detect the active component urushiol using profluorescent nitroxides.


                    Western Poison Oak                                             Contact Dermatitis from Poison Oak

Initial reactions using catechol as a model for urushiol show extremely promising results. We envision development of a spray that will allow detection of microgram quantities of urushiol from skin, tools and clothing, enabling removal of the oil before a skin rash develops.  A preliminary patent has been filed on this exciting methodology.

A variety of other detection methodologies based on profluorescent nitroxides are now under development in the laboratory.