Platinum thin film–based matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry imaging for improved ion yields of adrenocortical steroids

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Abstract
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) imaging enables spatially resolved molecular analysis; however, its sensitivity depends strongly on matrix uniformity and ionization efficiency, which pose challenges for low-abundance compounds such as steroid hormones. In this study, we developed a platinum (Pt) thin film–based surface-assisted laser desorption/ionization mass spectrometry (SALDI/MS) and matrix-enhanced SALDI/MS (ME-SALDI/MS) method to increase ion yields and improve steroid imaging with minimal sample pretreatment. Using sputter-deposited Pt films, 20 endogenous steroids were comprehensively detected without chemical derivatization. Furthermore, derivatized steroids analyzed by ME-SALDI/MS exhibited significantly higher ion yields than those obtained by conventional MALDI/MS or SALDI/MS, demonstrating a synergistic enhancement of desorption and ionization efficiency. ME-SALDI/MS imaging of porcine adrenal gland tissue enabled visualization of multiple derivatized steroids with high ion yields—including progesterone, corticosterone, and cortisol—reflecting their biosynthetic localization across cortical zones. Collectively, these results highlight the potential of Pt thin film–based SALDI and ME-SALDI/MS as robust tools that provide high ion yields for imaging of steroids and other biomolecules with inherently low desorption and ionization efficiency. Graphical abstract
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  • Kanazawa University

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