Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is a powerful tool for analyzing large bio-molecules and has been used in various clinical diagnostic applications.However, the direct detection of the high-molecular weight biomolecules by MALDI-MS suffers from the inherent limitation arising from the required use of matrix which assists the ionization of analytes upon laser irradiation.In order to circumvent this problem, we have designed and synthesized new mass tags based on ferrocene skeleton that can be photochemically ionizable upon UV-irradiation.After chemical conjugation of the mass tags with biomolecules of interest such as peptides, UV-laser irradiation of the resulting conjugates efficiently and selectively generated the corresponding mass-tag fragments without aid of matrix.We envision that this strategy would provide a new platform that allows multiple detection of biomarkers with high sensitivity and selectivity.