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When Johannes Gutenberg designed the first printing press over 500 years ago his big dreams and hopes probably never included the tiny nanoparticles we can print today using screen printers. The DST/Mintek Nanotechnology Innovation Centre (NIC) in Randburg have now obtained a screen printer to make tiny electrodes for their diagnostic products.

Screen printing has been around for a long time, and the technique was originally used in art. These days it is widely used in printing products like T-shirts, but it is also applied in producing more intricate products, such as screen printed electrodes and electronic circuit boards. The principles behind all types of screen printing are the same (see picture). A mesh or grid with a stencil of the required design is stretched over a screen. Under the screen is the substance onto which the product will be produced (substrate). Ink or a paste is put onto the mesh and an object called a squeegee moves across the screen and pushes the screen down onto the substrate. The squeegee also pushes the ink through the open areas of the grid, forming the pattern.

Screen printed electronics are made using a paste or ink with conductive properties. Nanomaterials such as metal nanoparticles, nanowires or carbon nanotubes can be included in the paste to improve the sensitivity of electrodes. An insulating paste is deposited as the final layer, in order to define the working area of the electrode.

Screen printed electrodes using nano-sized particles have been designed to make diagnostic sensors for glucose, cholesterol and to measure ethanol levels, as well as pesticides and pollutants. At the DST/Mintek NIC scientists use the screen printer to make various types of biosensors for health and water diagnostics and already have a working prototype for measles diagnosis.

Writer: Febe Wilken

A diagram of how basic screen printing works. Image derived from a diagram courtesy of Dr. Sibulelo Vilakazi