cm7b02174_si_001.pdf (1.67 MB)
Purple‑, Blue‑, and Green-Emitting Multishell Alloyed Quantum Dots: Synthesis, Characterization, and Application for Ratiometric Extracellular pH Sensing
journal contribution
posted on 2017-08-30, 13:46 authored by Kimihiro Susumu, Lauren D. Field, Eunkeu Oh, Michael Hunt, James B. Delehanty, Valle Palomo, Philip E. Dawson, Alan L. Huston, Igor L. MedintzWe
report the synthesis of a series of CdxZn1–xSe/CdyZn1–yS/ZnS and ZnSe/CdyZn1–yS/ZnS
multishell alloyed luminescent semiconductor quantum dots (QDs) with
fluorescence maxima ranging from 410 to 530 nm which cover the purple,
blue, and green portion of the spectrum. Their subsequent surface
modification to prepare water-soluble blue-emitting QDs, characterization,
and application for ratiometric pH sensing in aqueous buffers and
in an extracellular environment are further described. QDs were synthesized
starting from ZnSe cores, and the fluorescence peak positions were
tuned by (i) cation exchange with cadmium ions and/or (ii) overcoating
with CdyZn1–yS layers. The as-prepared QDs had reasonably high fluorescence
quantum yields (∼30–55%), narrow fluorescence bands
(fwhm ∼25–35 nm), and monodispersed semispherical shapes.
Ligand exchange with hydrophilic compact ligands was successfully
carried out to prepare a series of water-soluble blue-emitting QDs.
QDs coated with the hydrophilic compact ligands preserved the intrinsic
photophysical properties well and showed excellent colloidal stability
in aqueous buffers for over a year. The blue-emitting QDs were further
conjugated with the pH-sensitive dye, fluorescein isothiocyanate (FITC),
to construct a fluorescence resonance energy transfer-based ratiometric
pH sensing platform, and pH monitoring with the QD-FITC conjugates
was successfully demonstrated at pHs ranging between 3 and 7.5. Further
assembly of the QD-FITC conjugates with membrane localization peptides
allowed monitoring of the pH in extracellular environments. High quality,
water-soluble blue-emitting QDs coated with compact ligands can help
expand the practical fluorescence range of QDs for a variety of biological
applications.