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Clicks and Mortar in the World of Nanoparticles
May 7, 2015   
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Nanoparticles of various types can be quickly and permanently bonded to a solid substrate if one of the most effective methods of synthesis, click chemistry, is used for this purpose, according to a team of researchers from the Polish Academy of Sciences’ Institute of Physical Chemistry in Warsaw.

The researchers have found a way to quickly and effectively bond gold nanoparticles to a glassy carbon substrate.

Click chemistry is one of the newest methods of synthesis in modern chemistry. With this method, molecules are combined to form new chemical compounds by means of chemical “fasteners.” The method has so far been used mainly for the synthesis of more complex organic compounds. Now researchers at the Polish Academy of Sciences’ Institute of Physical Chemistry in Warsaw have managed to show that click chemistry chemical “fasteners” can quickly, effectively and permanently bond much larger structures: gold nanoparticles to a glassy carbon substrate.

The main idea of click chemistry was formulated in the late 1990s. It was inspired by nature—including by the large number of proteins that arise from the diverse combination of amino acids with the same bond (peptide). Click chemistry has many advantages. Many reactions take place at low temperatures, and in a single solvent—environmentally friendly water, for example. What’s more, the effectiveness of the reaction is high: usually around 80-90 percent. The versatility, efficiency and selectivity of click chemistry has made it popular, especially in the synthesis of new organic compounds.

“Click chemistry is similar to constructing new structures from building blocks. The blocks can be various chemical compounds as long as they have matching snaps. A problem arises when they don’t. Then you have to consider whether you can somehow attach the right snaps to a given building block,” said Joanna Niedziółka-Jönsson, D.Sc., from Institute of Physical Chemistry.

Another Institute of Physical Chemistry researcher, Adam Le¶niewski, Ph.D., winner of the Iuventus Plus grant from the Polish Ministry of Science and Higher Education, which was used to finance the research, said, “Usually, nanoparticles are simply deposited on the substrate and they attach to it by quite weak physical, for example electrostatic, interactions. We decided to show that with click chemistry they can be bonded to the substrate with covalent chemical bonds and thus permanently.”

To form the bond, the Institute of Physical Chemistry researchers used well-known chemical “snap fasteners:” groups of three nitrogen atoms (azides), which in the presence of a catalyst can combine with groups of carbon atoms (terminal alkynes) located at the end of other molecules. When they are connected, the two groups form stable nitrogen-carbon (triazole) rings. In the research, the azide groups were located on a glassy carbon substrate, and the terminal alkynes were introduced onto the surface of gold nanoparticles.

To generate the catalyst for the reaction, the researchers used an electrochemical method in which the role of the substrate was played by an appropriately prepared carbon electrode.

Justyna Matyjewicz, a Ph.D. student at the Institute of Physical Chemistry, said, “We managed to adjust the conditions of the whole process so that the suspension of gold nanoparticles in the solution surrounding the electrode remained stable. At the same time, we maintained an appropriate concentration of copper-two ions and supporting electrolyte. In this environment, the production of the right catalyst, complexes of copper-one, and the bonding of nanoparticles itself to the substrate was very efficient.”

Using a flow of current has significantly shortened the reaction time of the nanoparticles bonding to the substrate.

Niedziółka-Jönsson said, “We have been working with gold nanoparticles and carbon substrates, but our method is universal and in the future it can be used to produce substrates from other materials.”

Substrates produced by the Warsaw chemists make it easier to detect nitrites in the presence of sulfites. Sensors constructed on the basis of such substrates can be used, for example, to detect the presence of preservatives in foodstuffs. In the future, the type of click chemistry proposed by the Institute of Physical Chemistry researchers may be used in the production of new, stable substrates for a variety of chemical sensors and electrodes employed in flow systems.
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