The mass spectrum of MinE07UA showed a mass of 15,136.2 Da which suggests that some nucleotides coupling had failed as the MinE07Library mass range is 15677-16693.2 Da (S3, Fig. ). Upon analysis of the MS/MS fragment data using RoboOligo, it was found that the aptamer had been capped at base 45 (fC) meaning 5'-rGrGrA was missing. The sequences MinE07UA and MinE07UB are similar in that they both have three fU-Ph modified uridines, two of which are in the same location, and both have at least one fU-I modification (Fig. ).