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

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.