We report synthesis of a series of CdxZn1-xSe/CdyZn1-yS/ZnS multi-shell quantum dots (QDs) with fluorescence ranging from 410 to 530 nm, their surface modification to prepare water-soluble blue-emitting QDs, and their use for ratiometric pH sensing in aqueous buffers and in extracellular environments. The multi-shell QDs were synthesized in hydrophobic solvents starting from ZnSe cores, and the fluorescence peak positions were mainly 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, narrow fluorescence band, and monodispersed semi-spherical shapes. Ligand exchange of the as-prepared QDs with hydrophilic compact ligands was successfully performed to prepare water-soluble blue-emitting QDs. The blue-emitting QDs coated with the hydrophilic compact ligands preserved the intrinsic photophysical properties well and showed excellent colloidal stability in aqueous buffers. The blue-emitting QDs with amine-terminated poly(ethylene glycol) ligands were further conjugated with fluorescein isothiocyanate (FITC) to construct a ratiometric pH sensing platform, and pH monitoring with the QD-FITC conjugates was demonstrated at pH between 3 and 7.5. Further assembly of the QD-FITC conjugates with oligohistidine-tagged membrane localization peptides allowed us to localize the QD-FITC conjugates on cellular membranes and monitor pH in extracellular environments. Given the fact that high quality water-soluble blue-emitting QDs coated with compact ligands have been scarcely developed so far, our newly developed QDs would help expand the practical fluorescence tuning range of QDs for a variety of biological sensing and imaging applications.

Blue-emitting multi-shell quantum dots made from ZnSe cores: Synthesis and application for ratiometric pH sensing

254th National Meeting (2017)

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