In order to position amino acid particles in a spatially defined manner, we also used a CMOS chip instead of a laser printer. There, it is the array of pixel electrodes just underneath the chip’s surface that can be used to direct electrically charged particles to their address on the chip’s surface. Similar to the laser printer a whole layer of different amino acid particles is addressed first, and then the whole layer is melted at once to start the coupling reaction for the combinatorial synthesis of very high-density peptide arrays [22, 23]. This chip based peptide synthesis was done in cooperation with the Kirchhoff-Institute for Physics at the University of Heidelberg (Prof. Michael Hausmann). Fig. 13 shows an array of 10.000 peptides per cm2 that was synthesised directly on the chip’s surface. In order to be more flexible in the choice of the array support and to save costs, we developed a “chip printer“ in cooperation with the Institute for printing science technology at the Technical University of Darmstadt (Prof. Dr.-Ing. Edgar Dörsam). This “chip printer” can print the particles that first were deposited on selected pixel electrodes on the chip surface to any flat solid support (Fig. 14 & 15). Within the next years we will advance this technology with the final goal of a chip printer that routinely synthesises affordable very high-density peptide arrays that might lead to novel applications for peptide arrays that are not imaginable today.
Fig. 13; Synthesis of a peptide array with a computer chip. A: An array of 10.000 peptides per cm2 stained with two different antibodies. B: Circuit board with bonded chip.
Fig. 14; Photograph (left) and schematic drawing (right) of a “chip-synthesis machine”. A chip‘s pixel-electrodes pick up particles from a glass slide that is uniformly covered with amino acid particles. Then the chip moves to a 2nd support were the particles are printed onto a glass slide. After consecutively printing all the different amino acid particles, peptide synthesis is started by melting the whole particle layer. Charged amino acid particles move in the electrical field according to the formula Fad = Q x E whereby the adhesion force Fad that keeps the particles sticking to the surface must be smaller then the electrical force that drags charged particles away.
Fig. 15; Amino acid particles deposited on the chip’s surface (upper left) were printed to a glass slide (upper right), melted (lower left), and amino acids coupled to the surface stained with bromophenoleblue (lower right)..
 Beyer M, Nesterov A, Block I, König K, Felgenhauer T, Fernandez S, Leibe K, Torralba G, Hausmann M, Trunk U, Lindenstruth V, Bischoff FR, Stadler V und Breitling F. (2007) Combinatorial synthesis of peptide arrays onto a computer chip’s surface. Science 318, 1888.
 Breitling F, Nesterov A, Stadler V, Felgenhauer T und Bischoff FR. (2010) High-density peptide arrays. Molecular BioSystems 5, 224-234. Epub 2009 Jan 16. Review