Evaluation of spotting buffers for 70-mer oligonucleotides. A: Serial dilutions of 5'-fluorescein labeled S. aureus tracking oligonucleotide were printed in 15% DMSO/1.5 M betaine (I), 50% DMSO (II), or 3X SSC (III) print buffers at the indicated concentrations and spotted onto poly L-lysine coated glass slides. Slides were processed, blocked, and scanned for fluorescein fluorescence. B: Percent retention of 5'-fluorescein-labeled tracking oligonucleotide on poly L-lysine coated glass slides were determined for each print buffer using 25 replicate arrays. Retention of oligonucleotide in each print buffer was calculated by determining relative fluorescence units (RFU's) at 0.625 μM (row d), 0.313 μM (row e), and 0.156 μM (row f) from replicate arrays. Values are expressed as percent RFU (+/- standard deviation) after normalization to the 3X SSC print buffer. Highest retention was obtained with the 15% DMSO/1.5 M betaine print buffer.