Detection of a Biomolecule, Allantoin, in Skin Tissue Using Water Gas Cluster Ion Beam Time‐Of‐Flight Secondary Ion Mass Spectrometry

ABSTRACT Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is a powerful tool for imaging molecules in biological tissues owing to its high spatial resolution and sensitivity. Effective detection of key molecules in a sample is crucial for detailed evaluation of complex samples such as tissues. In this study, a target is a biomolecule, allantoin (C 4 H 6 N 4 O 3 ), and the allantoin [M + H] + and [M‐H] − are adequately detected using ToF‐SIMS with a Bi cluster ion beam from an allantoin control sample. However, the detection of ions related to allantoin permeated in human skin tissue is not straightforward because there are interfering mass peaks in the ToF‐SISM spectra of control skin samples that make allantoin detection challenging, and the allantoin fragment ions have the same chemical structure as the fragment ion from other biomolecules in the tissue. In order to sufficiently detect the allantoin‐related ions, we focused on ion beams with a higher ionization yield, such as gas cluster ion beams (GCIBs). As a result, a ToF‐SIMS with water GCIB was significantly more effective in detecting the allantoin [M + H] + and [M‐H] − in the skin samples in both positive and negative ion spectra. The results revealed that the water GCIB approach is better suited for studying biological samples, as it effectively distinguishes the mass peaks of allantoin related ions using ToF‐SIMS.