Metallic nanoparticles are materials of many uses; ranging from catalyzing chemical reactions to forming unique dyes that can be used for sensing and electro-optics. These particles are usually synthesized in solution but it is also possible to form them directly on surfaces. Since the shape and size of the nanoparticles determine their properties, it is of major importance to understand the mechanism controlling these features.
In a paper by Prof. Daniel Mandler’s group, they present a method for patterning gold nanoparticles of different shapes on non-conducting surfaces. The particles are grown by dipping a thin gold electrode in a solution of a reducing agent. Concurrently, a surface modified with thiols –chemical groups with high affinity to gold, is dipped in the same solution. Once formed, the particles bind to the thiols, anchoring themselves to the surface.
In addition, the researchers examined the conditions affecting the shape of the particles. Changing the reductants and their concentrations, as well as altering the electrode voltage, resulted in particles that differed in size and shape. For example, under different concentrations and voltages, sodium borohydride gave cubical, spherical and pentagonal crystals. It turned out that the rate of the redox reaction influenced the crystal structure of the particles. A strong reductant induced a fast uncontrolled redox that lead to simple structures like spheres, whereas a weak reductant induced slow controlled reaction that resulted in more complexed geometrical structures such as cubes and hexagons.
By utilizing these nanoparticles properties (e.g. optical, catalytic…) it is now possible to use this methodology to functionalize non-conducting surfaces for various fields.