Peptides (25 µM) were printed in commercial protein printing buffer (ArrayIt) including 1 mg/mL BSA onto SuperStreptavidin glass slides (ArrayIt) using an OmniGrid100 arrayer (Genomic Solutions) and SMP6 Stealth Pins (ArrayIt).  Each peptide was printed by two different pins and samples were printed in both forward and reverse direction to monitor sample carryover.  A biotin-fluorescein tracer molecule was added as a positive control for spotting.

Modification-specific antibodies were incubated with printed peptide arrays for 2 hours at 4˚C in PBS containing BSA (1%) and Tween-20 (0.3%).  Arrays were washed three times with PBS and probed with appropriate Alexafluor 647-conjugated secodary antibodies for 30 min at 4˚C protected from light.  Arrays were washed three times with PBS and dried with air before visualization on a Typhoon Trio+ imager.  Binding was quantified using ImageQuant software and statistics were calculated using Prism.