IR-MALDESI Mass Spectrometry Imaging of Biological Tissue Sections Using Ice as a Matrix

Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging of biological tissue sections using a layer of deposited ice as an energy-absorbing matrix was investigated. Dynamics of plume ablation were first explored using a nanosecond exposure shadowgraphy system designed to simultaneously collect pictures of the plume with a camera and collect the Fourier transform ion cyclotron resonance FT-ICR mass spectrum corresponding to that same ablation event. Ablation of fresh tissue analyzed with and without using ice as a matrix were compared using this technique. Effect of spot-to-spot distance, number of laser shots per pixel, and tissue condition (matrix) on ion abundance were also investigated for 50 μm-thick tissue sections. Finally, the statistical method called design of experiments was used to compare source parameters and determine the optimal conditions for IR-MALDESI of tissue sections using deposited ice as a matrix. With a better understanding of the fundamentals of ablation dynamics and a systematic approach to explore the experimental space, it was possible to improve ion abundance by nearly one order of magnitude.