Shape-Dependent Catalytic Activity of Gold and Bimetallic Nanoparticles in the Reduction of Methylene Blue by Sodium Borohydride

In this study the catalytic activity of different gold and bimetallic nanoparticle solutions towards the reduction of methylene blue by sodium borohydride as a model reaction is investigated. By utilizing differently shaped gold nanoparticles, i.e., spheres, cubes, prisms and rods as well as bimetallic gold–palladium and gold–platinum core-shell nanorods, we evaluate the effect of the catalyst surface area as available gold surface area, the shape of the nanoparticles and the impact of added secondary metals in case of bimetallic nanorods. We track the reaction by UV/Vis measurements in the range of 190–850 nm every 60 s. It is assumed that the gold nanoparticles do not only act as a unit transferring electrons from sodium borohydride towards methylene blue but can promote the electron transfer upon plasmonic excitation. By testing different particle shapes, we could indeed demonstrate an effect of the particle shape by excluding the impact of surface area and/or surface ligands. All nanoparticle solutions showed a higher methylene blue turnover than their reference, whereby gold nanoprisms exhibited 100% turnover as no further methylene blue absorption peak was detected. The reaction rate constant k was also determined and revealed overall quicker reactions when gold or bimetallic nanoparticles were added as a catalyst, and again these were highest for nanoprisms. Furthermore, when comparing gold and bimetallic nanorods, it could be shown that through the addition of the catalytically active second metal platinum or palladium, the dye turnover was accelerated and degradation rate constants were higher compared to those of pure gold nanorods. The results explore the catalytic activity of nanoparticles, and assist in exploring further catalytic applications.

Metallic Microswimmers Driven up the Wall by Gravity

Experiments on autophoretic bimetallic nanorods propelling within a fuel of hydrogen peroxide show that tail-heavy swimmers preferentially orient upwards and ascend along inclined planes. We show that such gravitaxis is...

Enhancement of electromagnetic interference shielding from the synergism between Cu@Ni nanorods and carbon materials in flexible composite films

A series of composite films containing poly(vinylidene fluoride) (PVDF), carbon nanotubes, graphene and bimetallic nanorods, in which copper was wrapped with nickel (Cu@Ni), were fabricated via solution casting and compression molding.

A H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods for highly sensitive sensing of matrix metalloproteinase 2

We construct for the first time a H2O2-free electrochemical peptide biosensor based on Au@Pt bimetallic nanorods in neutral substrate solutions for highly sensitive detection of matrix metalloproteinase 2.

Shape-programmed 3D printed swimming microtori for the transport of passive and active agents

Through billions of years of evolution, microorganisms mastered unique swimming behaviors to thrive in complex fluid environments. Limitations in nanofabrication have thus far hindered the ability to design and program synthetic swimmers with the same abilities. Here we encode multi-behavioral responses in microscopic self-propelled tori using nanoscale 3D printing. We show experimentally and theoretically that the tori continuously transition between two primary swimming modes in response to a magnetic field. The tori also manipulated and transported other artificial swimmers, bimetallic nanorods, as well as passive colloidal particles. In the first behavioral mode, the tori accumulated and transported nanorods; in the second mode, nanorods aligned along the toriʼs self-generated streamlines. Our results indicate that such shape-programmed microswimmers have a potential to manipulate biological active matter, e.g. bacteria or cells.

Ultrasensitive SERS detection of specific oligonucleotides based on Au@AgAg bimetallic nanorods

We synthesized a novel and sensitive Au/Ag bimetallic SERS-active nanotag, Au–Ag–Ag core–shell–shell nanorod (Au@AgAgNR).