We present an experimental route to engineer the exciton energies of single quantum dots in nanowires. By integrating the nanowires onto a piezoelectric crystal, we controllably apply strain fields to the nanowire quantum dots. Consequently, the exciton energy of a single quantum dot in the nanowire is shifted by several meVs without degrading its optical intensity and single-photon purity. Second-order autocorrelation measurements are performed at different strain fields on the same nanowire quantum dot. The suppressed multi-photon events at zero time delay clearly verify that the quantum nature of single-photon emission is well preserved under external strain fields. The work presented here could facilitate on-chip optical quantum information processing with the nanowire based single photon emitters.

In nanofluidic electrochemical sensors based on redox cycling, zeptomole quantities of analyte molecules can be detected as redox-active molecules travel diffusively between two electrodes separated by a nanoscale gap. These sensors are employed to study the properties of multiferrocenylic compounds in nonpolar media, 2,3,4-triferrocenylthiophene and 2,5-diferrocenylthiophene, which display well-resolved electrochemically reversible one-electron transfer processes. Using stochastic analysis, we are able to determine, as a function of the oxidation states of a specific redox couple, the effective diffusion coefficient as well as the faradaic current generated per molecule, all in a straightforward experiment requiring only a mesoscopic amount of molecules in a femtoliter compartment. It was found that diffusive transport is reduced for higher oxidation states and that analytes yield very high currents per molecule of 15 fA.