One-cavity-one-peptide-method: Within BMBF projects ANTIBIOTIKA and KATMETHAN we developed yet another method that uses glass slides with 2,5 Mio small cavities of some 12µm diameter and 10µm depth. The basic idea behind this approach is simple: Only one “amino-acid-particle” with a size of 10µm fits into a cavity that is slightly larger. We therefore coded the different amino acid building blocks with different fluorescent dyes, then randomly applied a mixture of >20 different “amino-acid-particles” over the micro-structured glass slides, and then took a fluorescence scan to find out for all the cavities what type of amino acid building block they picked. [7; see also Fig. 3] All the subsequent steps are identical to the solid-material-based synthesis described above: (more) (i) heat or vapour solvent diffuses amino acid building blocks, (ii) these couple to the solid support and elongate the growing peptides by another monomer, (iii) transient Fmoc-protecting-group is removed, and (iv) the whole procedure is repeated.
The basic idea was published by Popov et al.,  however, the use of dry particles proved to be problematic. Therefore, we currently develop a microfluidic-based variant of this technology that should provide us with high-quality stochastic peptide arrays including posttranslational modified amino acids. With a cheap method to synthesize >2,5 Mio peptides per glass slide, we expect completely new applications for peptide arrays that should be feasible then (more).
Fig. 3; One-cavity-one-peptide-method. Cavities of a micro-structured glass slide are stochastically filled with slightly smaller “amino-acid-particles“. Different amino acid building blocks are colour-coded. Thereby, a fluorescence scan reveals the type of amino acid building block that each and every cavity picked. Next, amino acid building blocks are diffused by heat or solvent vapour in order to couple them to the growing peptides. If repeated, an array of peptides is synthesized.
 Popov R, Shankara GK, von Bojničić-Kninski C, Barua P, Mattes D, Breitling F, Nesterov-Müller A. (2019) Stochastic deposition of amino acids into microcavities via microparticles. Scientific Reports, 9: 16468; DOI: 10.1038/s41598-019-52994-w