Combining Laser-Induced Edition to Collision-Induced Sequencing of Digital Oligomers in a Single Gas-Phase Experiment

To increase the confidentiality level of molecular tags, binary information can be hidden in sequence-defined oligomers using isobaric monomers including a photo-sensitive one, which mass can be modified upon light irradiation. Reading such secured data requires light edition prior to MS/MS sequencing, which was investigated here in a single gas-phase workflow.

Oligo (phosphodiester)s made of units with either light-sensitive ortho- or light-inert para-nitrobenzyl side-group were electrosprayed as deprotonated oligomers and sampled in an ion trap instrument equipped with various light sources. Nanosecond-pulsed laser (266 or 365 nm) and CW laser (375 nm) irradiations were compared for their efficiency to induce photo-cleavage of all o-nitrobenzyl moieties in laser-induced dissociation and to produce sufficient amounts of edited oligomers to achieve full coverage of their sequence in collision-induced dissociation.

While cleavage of photo-sensitive moieties was never fully achieved with the pulsed laser, photo-cleavage of all o-nitrobenzyl side-groups readily occurred with the CW laser, as monitored by successive losses of o-nitrobenzaldehyde from the irradiated chains. Time required for maximal production of edited oligomers increased with their number of reactive units but shorter irradiation steps were found sufficient to produce enough secondary precursors to achieve full sequence coverage in MS/MS.

Laser-induced modification of light-sensitive units allowed monotonic sequences of two isobaric monomers to be turned into MS/MS readable sequences. This gas-phase experiment enables a much higher throughput compared with the 1-h irradiation requested for the oligomer edition when performed in solution.