During the presentation I will tell the story on how a voltage-less method of spatially precise, reproducible, and repetitive deposition of microdroplets containing semiconductor quantum dots (QDs) can be combined with positioning of metallic nanowires in the quest to assemble on-demand hybrid nanostructures. Colloidal semiconductor QDs are known for their high emission quantum yields, photostability, and spectral tunability. On the other hand, silver nanowires (AgNWs) exhibit strong and spectrally broad plasmon resonance as well as facilitate microns-long energy propagation via surface plasmon polaritons (SPPs).

The concept of microdroplet deposition is based on using hydrophobic microcapillaries whose positions are controlled with piezoelectric actuators. In this way microdroplets with diameters less than 500 nm containing quantified amounts of QDs, down to single emitters can be fabricated. Importantly, upon deposition, such QD-containing microdroplets can be moved across the surface into desired locations with no morphological or optical degradation.

In the first experimental demonstration of the nanopositioning technology, we move a QD-containing microdroplet along a single AgNW while exciting the nanostructure into one end of the AgNW. As the distance between the excitation spot and the position of the microdroplet increases, the luminescence intensity of the microdroplet is reduced as a result of the Ohmic dumping of the electromagnetic wave. As a result, we determined – in a non-invasive way – the damping constant in a single AgNW, together with its spectral dependence.

The second hybrid nanostructure was assembled using two AgNW interfaced with a microdroplet placed in between them. In this experiment, upon optical excitation of the free end of the first AgNW we monitor the signal from the far end of the second AgNW. The results indicate that only upon placing a QD-containing microdroplet between the AgNWs the emission emerges from this second end. In other words, we detect optical signal from the position where neither the nanostructure is optically excited, nor the emitters are present.

Overall, the findings provide a roadmap for architectures where QDs (dots) and AgNWs (dashes) can be positioned at predefined locations with high precision. Such architectures, which come in virtually infinite number, can be applied for long-range transmission of optical signals, remote information processing or precise and selective optical biosensing.