title: Dimerization of Organic Dyes on Luminescent Gold Nanoparticles for Ratiometric pH Sensing.
abstract: Synergistic effects arising from the conjugation of organic dyes onto non-luminescent metal nanoparticles (NPs) have greatly broadened their applications in both imaging and sensing. Herein, we report that conjugation of a well-known pH-insensitive dye, tetramethyl-rhodamine (TAMRA), to pH-insensitive luminescent gold nanoparticles (AuNPs) can lead to an ultrasmall nanoindicator that can fluorescently report local pH in a ratiometric way. Such synergy originated from the dimerization of TAMRA on AuNPs, of which geometry was very sensitive to surface charges of the AuNPs and can be reversely modulated through protonation of surrounding glutathione ligands. Not limited to pH-insensitive dyes, this pH-dependent dimerization can also enhance the pH sensitivity of fluorescein, a well-known pH-sensitive dye, within a larger pH range, opening up a new pathway to design ultrasmall fluorescent ratiometric nanoindicators with tunable wavelengths and pH response ranges.
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA.
authors.forename: Shasha
authors.initials: S
authors.lastname: Sun
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA.
authors.forename: Xuhui
authors.initials: X
authors.lastname: Ning
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA.
authors.forename: Greg
authors.initials: G
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA.
authors.forename: Yen-Chung
authors.initials: YC
authors.lastname: Wang
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA.
authors.forename: Chuanqi
authors.initials: C
authors.lastname: Peng
authors.affiliation: Department of Chemistry, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, TX, 75080, USA. jiezheng@utdallas.edu.
authors.forename: Jie
authors.initials: J
authors.lastname: Zheng
mesh_terms: D004396:Coloring Agents / Q000737:chemistry*; D019281:Dimerization; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D049449:Luminescence; D053768:Metal Nanoparticles; D046529:Microscopy, Electron, Transmission; D013050:Spectrometry, Fluorescence
chemical_list: D004396:Coloring Agents; D006046:Gold
keywords: dimerization; dyes; gold nanoparticles; luminescence; pH sensors