title: Quantum-dot/dopamine bioconjugates function as redox coupled assemblies for in vitro and intracellular pH sensing.
abstract: The use of semiconductor quantum dots (QDs) for bioimaging and sensing has progressively matured over the past decade. QDs are highly sensitive to charge-transfer processes, which can alter their optical properties. Here, we demonstrate that QD-dopamine-peptide bioconjugates can function as charge-transfer coupled pH sensors. Dopamine is normally characterized by two intrinsic redox properties: a Nernstian dependence of formal potential on pH and oxidation of hydroquinone to quinone by O(2) at basic pH. We show that the latter quinone can function as an electron acceptor quenching QD photoluminescence in a manner that depends directly on pH. We characterize the pH-dependent QD quenching using both electrochemistry and spectroscopy. QD-dopamine conjugates were also used as pH sensors that measured changes in cytoplasmic pH as cells underwent drug-induced alkalosis. A detailed mechanism describing the QD quenching processes that is consistent with dopamine's inherent redox chemistry is presented.
authors.affiliation: Center for Bio/Molecular Science and Engineering Code 6900, US Naval Research Laboratory, Washington, District of Columbia 20375, USA. igor.medintz@nrl.navy.mil
authors.forename: Igor L
authors.initials: IL
authors.lastname: Medintz
authors.forename: Michael H
authors.initials: MH
authors.lastname: Stewart
authors.forename: Scott A
authors.initials: SA
authors.lastname: Trammell
authors.forename: Kimihiro
authors.initials: K
authors.lastname: Susumu
authors.forename: James B
authors.initials: JB
authors.lastname: Delehanty
authors.forename: Bing C
authors.initials: BC
authors.lastname: Mei
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Melinger
authors.forename: Juan B
authors.initials: JB
authors.lastname: Blanco-Canosa
authors.forename: Philip E
authors.initials: PE
authors.lastname: Dawson
authors.forename: Hedi
authors.initials: H
authors.lastname: Mattoussi
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D015374:Biosensing Techniques / Q000295:instrumentation*; D019556:COS Cells; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D004298:Dopamine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008422:Materials Testing; D036103:Nanotechnology / Q000295:instrumentation*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D045663:Quantum Dots; D013053:Spectrophotometry
chemical_list: D001672:Biocompatible Materials; D010455:Peptides; D010100:Oxygen; D004298:Dopamine