cross-contamination of oligonucleotides

Custom oligonucleotides (oligos) are widely used reagents in biomedical research, diagnostics, and therapeutics. Some typical applications of oligos include polymerase chain reaction (PCR), sequencing, hybridization, microarray, and library construction. The reliability of oligos in such applications depends on their purity and specificity. We found that commercially available oligos are frequently contaminated with non-specific sequences (i.e., other unrelated oligonucleotides). These contaminants were detected in oligos across the grade spectrum, and the problem was observed in leading commercial oligo suppliers across the globe. Deep sequencing of some of the oligos revealed a variety of contaminants. These findings may alert concerns about the previously published results, relying on oligo purity.