Search

We 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 pres...

Doping of fluorescent noble metal nanoclusters is being pursued to manipulate the structure of such materials along with improving physicochemical characteristics such as long-term stability and photoluminescence quantum yield. Here, we synthesize metal-doped and alloyed ultrasmall gold nanoclusters (AuNCs) directly in water using a facile one-step coreduction reaction with bidentate dithiolane PEGylated ligands that terminate in different functional groups including a methoxy, carboxy, amine, and azide. Two primary types of cluster materials were the focus of synthesis and characterization: first, a series of doped/alloyed Ag-doped AuNCs, where the ratio of Au:Ag was varied across a wide range including 99:1, 98:2, 90:10, 80:20, 50:50, 20:80, 10:90, and 2:98 along with pure AuNC and AgNC controls; second, doped Au:D NCs, where D included Pt, Cu, Zn, and Cd. Physical characterization of the modified AuNCs included TEM analysis of size, XPS/EDX analysis of dopant content, and a detailed analysis of photoph...

The rigidity and defined length of the polyproline type II helix (PPII) have made it the structural basis of a nanoscopic ruler, which has been widely applied in Forster resonance energy transfer (FRET) studies. A growing body of data, however, has questioned the foundation for this and has provided evidence for structural perturbations to the PPII caused by temperature, salt content, solvent polarity, and even Pro repeat length. Here, we examine the polyproline ruler in the context of semiconductor quantum dots (QDs) and FRET. For this study, a series of polyproline peptides (Pron, n = 0, 3, 6, 9, 12, 15, 18) displaying a C-terminal hexahistidine sequence (His6) and an N-terminal cysteine for site-specific labeling with Cy3 dye were synthesized. Peptide rigidity was first examined with ATTO 647 Ni2+-nitrilotriacetic acid acceptor dye coordinated to the His6-termini of the Cy3 donor-labeled peptides. These conditions provided a steady-state fluorescent response that closely followed FRET predictions deriv...

Luminescent semiconductor quantum dots (QDs) play an important role in optical biosensing and, in particular, in FRET (Forster resonance energy transfer)-based luminescent probes. The QD materials that form the basis for these probes are in actuality quite heterogeneous and consist of different types of QDs with variations in material compositions, surface coatings, and available biofunctionalization strategies. To optimize their role in active sensors that rely on FRET, extensive physicochemical characterization is required. A technique that can provide precise information about size, shape, and bioconjugation properties of different QD-biomolecule conjugates from a single sample and measurement under actual experimental biosensing conditions would therefore be highly important for advancing QDs to a next generation nanobiosensing tool. Here, we present a detailed FRET study on a large set of QD-biomolecule conjugates, which allows for a homogeneous solution-phase size, shape, and bioconjugation analysis of peptide and protein self-assembled QDs at subnanomolar concentrations and with subnanometer resolution. Direct incorporation of luminescent Tb-complexes (Tb) in the peptides or proteins leads to Tb-to-QD FRET upon assembly to the different QD surfaces. Luminescence decay times and time-gated intensities, which precisely decode the FRET interactions, provide a wealth of useful information on the underlying composite structure and even biochemical functionality. In contrast to other high-resolution techniques, which require rather sophisticated instrumentation, well-defined experimental conditions, and low sample throughput, our technique uses a commercial time-resolved fluorescence plate reader for very fast and simple data acquisition of many aqueous samples in a standard microtiter plate.