Controlled Binding Between Adjacent Metal Nanoparticles

Nanoparticles capped with organic ligands can be applied to substrates using several methods and these methods are:

1. One method is to apply the nanoparticles as-is, without forming any linkage between them.
2. Second method is based on creating a highly ordered sheet of nanoparticles by utilizing the protecting ligand as bonder or liner that connects adjacent nanoparticles. This arrangement of linked nanoparticles is illustrated in the following figure. 

Achieving intra-linked nanoparticles involves an exchange reaction followed by interparticle linkages, including: thiolate-Au bonding, hydrogen bonding of carboxylic acid terminal groups and selective dicarboxylate-silver bonding.

In previous figure nanoparticles are illustrated with yellow spheres and are covered with two protecting ligands. One ligand is connected only to one nanoparticle by Sulphur (S) bond and the ligand length is represented by the letter n. The other ligand is connected to two different nanoparticles (as indicated by the letter X) and the length of these ligands is represented with the letter m. As can be seen in the image, when n<m the nanoparticles matrix will be extremely dense. When n > m the nanoparticles matrix will be much more flexible. This properties are important when using nanoparticles as devices and sensors. Control over the values of n and m will determine the properties of the nanoparticle-based devices. Examples of properties affected by the ligand are electrical properties such as electrical resistance and ability to sense different molecules.