We measured the quantum-confined Stark effect (QCSE) of several types of fluorescent colloidal semiconductor quantum dots and nanorods at the single molecule level at room temperature. These measurements demonstrate the possible utility of these nanoparticles for local electric field (voltage) sensing on the nanoscale. Here we show that charge separation across one (or more) heterostructure interface(s) with type-II band alignment (and the associated induced dipole) is crucial for an enhanced QCSE. To further gain insight into the experimental results, we numerically solved the Schrödinger and Poisson equations under self-consistent field approximation, including dielectric inhomogeneities. Both calculations and experiments suggest that the degree of initial charge separation (and the associated exciton binding energy) determines the magnitude of the QCSE in these structures.

C olloidal semiconductor quantum dots (QDs) and nanorods (NRs) are nanometer-sized single-crystal nanoparticles (NPs) nucleated from a hot solution of precursor molecules. Their size and shape can be precisely controlled by the duration, temperature, and ligands used in the synthesis. 1À3 This method yields QDs orNRs that have composition and size-dependent absorption and emission wavelengths covering the entire spectral range from the visible to the NIR regions.

We developed a new peptide, natural phytochelatin (PC), which tightly binds to CdSe/ZnS quantum dots’ (QDs) surfaces and renders them water-soluble. Coating QDs with this flexible and all-hydrophilic peptide offers high colloidal stability, adds only 0.8–0.9 nm to the radius of the particles (as compared to their original inorganic radius), preserves very high quantum yield (QY) in water, and affords facile bioconjugation with various functional groups. We demonstrate specific targeting (with minimal non-specific binding) of such fluorescein-conjugated QDs to ScFv-fused mouse prion protein expressed in live N2A cells. We also demonstrated homogeneous in-vivo biodistribution with no significant toxicity in live zebrafish.