title: Probing the Quenching of Quantum Dot Photoluminescence by Peptide-Labeled Ruthenium(II) Complexes.
abstract: Charge transfer processes with semiconductor quantum dots (QDs) have generated much interest for potential utility in energy conversion. Such configurations are generally nonbiological; however, recent studies have shown that a redox-active ruthenium(II)-phenanthroline complex (Ru2+-phen) is particularly efficient at quenching the photoluminescence (PL) of QDs, and this mechanism demonstrates good potential for application as a generalized biosensing detection modality since it is aqueous compatible. Multiple possibilities for charge transfer and/or energy transfer mechanisms exist within this type of assembly, and there is currently a limited understanding of the underlying photophysical processes in such biocomposite systems where nanomaterials are directly interfaced with biomolecules such as proteins. Here, we utilize redox reactions, steady-state absorption, PL spectroscopy, time-resolved PL spectroscopy, and femtosecond transient absorption spectroscopy (FSTA) to investigate PL quenching in biological assemblies of CdSe/ZnS QDs formed with peptide-linked Ru2+-phen. The results reveal that QD quenching requires the Ru2+oxidation state and is not consistent with Förster resonance energy transfer, strongly supporting a charge transfer mechanism. Further, two colors of CdSe/ZnS core/shell QDs with similar macroscopic optical properties were found to have very different rates of charge transfer quenching, by Ru2+-phen with the key difference between them appearing to be the thickness of their ZnS outer shell. The effect of shell thickness was found to be larger than the effect of increasing distance between the QD and Ru2+-phen when using peptides of increasing persistence length. FSTA and time-resolved upconversion PL results further show that exciton quenching is a rather slow process consistent with other QD conjugate materials that undergo hole transfer. An improved understanding of the QD-Ru2+-phen system can allow for the design of more sophisticated charge-transfer-based biosensors using QD platforms.
authors.affiliation: Department of Chemistry, University of Miami , 1301 Memorial Drive, Miami, Florida 33146, United States.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Scott
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: W Russ
authors.initials: WR
authors.lastname: Algar
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Stewart
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Trammell
authors.affiliation: Departments of Cell Biology and Chemistry, The Scripps Research Institute , La Jolla, California 92037, United States.
authors.forename: Juan B
authors.initials: JB
authors.lastname: Blanco-Canosa
authors.affiliation: Departments of Cell Biology and Chemistry, The Scripps Research Institute , La Jolla, California 92037, United States.
authors.forename: Philip E
authors.initials: PE
authors.lastname: Dawson
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Deschamps
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Ramasis
authors.initials: R
authors.lastname: Goswami
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States ; Sotera Defense Solutions , Columbia, Maryland 21046, United States.
authors.forename: Eunkeu
authors.initials: E
authors.lastname: Oh
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Alan L
authors.initials: AL
authors.lastname: Huston
authors.affiliation: Center for Bio/Molecular Science and Engineering, Code 6900, Optical Sciences Division, Code 5611, and Material Sciences and Technology, Code 6351, U.S. Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Igor L
authors.initials: IL
authors.lastname: Medintz