Preparation and Characterization of Janus Dumbbells Nanomotors

The research on Janus nanoparticles has been gaining substantial momentum in the last years. Their non-homogeneously functionalized surface renders them much more interesting than their isotropic counterparts. One unique possibility offered by these particles is their transformation into nanomotors. In this work, we will discuss the synthesis, functionalization, characterization and self-assembly of Janus Dumbbells asymmetrically functionalized to become nanomotors.

We start by synthesizing polystyrene dumbbell-shaped nanoparticles in a three-step process, as has already been reported [1]. We then performed silane chemistry to selectively bring amino groups on the surface of one hemisphere of the dumbbells only. This is possible thanks to presence of silanol groups on the surface of the first hemisphere. One hemisphere of the dumbbells has then been selectively covered with gold nanocrystals. We prepared negatively-charged gold nanocrystals (coated with citric acid) by a Turkevich-like method. Due to the electrostatic interactions between the amino groups on the polystyrene dumbbells and the citrate groups on the gold nanocrystals, mixing the Janus dumbbells with the gold nanocrystals leads the latter selectively attached on one hemisphere of the former particles, while the other hemisphere remains naked. On top of interesting plasmonic properties, gold nanoparticles are also known to act as “seeds” for the growth of platinum nanoparticles. An asymmetric distribution of such catalytic nanoparticles leads to self-propulsion of the dumbbells in the presence of hydrogen peroxide as fuel.

In this work, Janus nanomotors with different sizes, from 100nm to several hundred of nanometers have been prepared, and their self-propelling ability in the presence of hydrogen peroxide have been tested using single-point fluorescent correlation spectroscopy. Additionally, their self-assembly in the presence of electrolytes with/without fuel has been investigated.

[1] F. Guignard, M. Lattuada, Langmuir 2015, 31(16):4635-43.