Label-Free Imaging of Solid-Phase Peptide Synthesis Products and Their Modifications Tethered in Microspots Using Time-of-Flight Secondary Ion Mass Spectrometry.

Time-of-flight secondary ion mass spectrometry is used to analyze solid-phase synthesis products in 60 µm spots of high-density peptide arrays. As a result, a table of specific fragments for the individual detection of amino acids and their side chain protecting groups within peptides is compiled. The specific signal of an amino acid increases linearly as its number increases in the immobilized peptide. Mass-to-charge ratio values are identified that can distinguish between isomers such as leucine and isoleucine. The accessibility of the N-terminus of polyalanine will be studied depending on the number of its residues. The examples provided in the study demonstrate the significant potential of time-of-flight secondary ion mass spectrometry for high-throughput screening of functional groups and their accessibility to chemical reactions occurring simultaneously in hundreds of thousands of microreactors on a single microscope slide.