Optimizing the substrate-mediated laser ablation of biological tissues: Quest for the best substrate material

Laser micro-sampling is a promising tool for ambient pressure chemical imaging of biological material by mass spectrometry. Conventional approaches use laser energy coupling into the analyzed sample through electronic (UV) or vibrational (IR) channels. In a recent study [B. Fatou, M. Wisztorski, C. Focsa, M. Salzet, M. Ziskind, I. Fournier, Sci. Rep. 5: 18135, 2015], we have demonstrated efficient micro-sampling of biological material through a substrate-mediate laser ablation (SMLA) mechanism using non-resonant visible radiation. Taking advantage of this effect, a large-scale proteomic analysis of micro-sampled tissue sections was performed, demonstrating the possible identification of about 400 proteins, including minor species, from an irradiated surface of 400 mu m diameter. Fundamental investigations on biological standards revealed the role of the substrate optical properties in the ejection process. In the present work, we extend these studies by considering the substrate thermal properties. A systematic investigation on the sampling efficiency of homogeneous tissue sections placed on top of various selected substrates was performed. Two ejection mechanisms are clearly evidenced and interpreted in the frame of a simple model based on the substrate properties and the laser beam profile. Improvement of the ejection yield and spatial resolution is also discussed in this frame, in view of the practical application of this technique in the field of (bio) chemical mass spectrometry imaging.