DEFIMAGE

TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) mass spectrometry imaging can be greatly improved by using massive argon clusters to sputter biological samples, which are further analyzed by a beam of bismuth clusters. Recent preliminary results showed that this dual beam depth profiling method provides for organic molecules such as lipids, 3-D ion images, and a significant increase in sensitivity, as well as cleaning without damage of the surface of precious samples. The DEFIMAGE project is multi- and interdisciplinary and aims to make a big breakthrough in TOF-SIMS imaging, thus opening the door for new original applications, in health science, and chemical analysis of cultural heritage artifacts. After the installation on the existing TOF-SIMS mass spectrometer of a new Argon Massive Cluster Ion Source (AMCIS), delivering clusters of hundreds to thousands of argon atoms at a few keV of energy, different experimental conditions for dual beam depth profiling onto tissue samples will be assessed: size and energy of the argon clusters used for sputtering, as well as size and energy of the bismuth cluster used for analyzing, and relative doses of each of the beams, will be optimized with rat brain tissue sections, used as a working model. This will be done according to three directions: 3-D analysis, or in depth analysis of thin tissue sections, enhancement of the sensitivity, by summing the signal of the whole sample depth during the sputtering (a large increase of more than 100 is expected), and cleaning of sample surface by soft sputtering with the argon clusters. Particular attention will be paid to possible migration of lipids during in-vacuum defrosting of samples, and to possible matrix effects induced by specific compounds like cholesterol. A first use of the newly developed method will be to scan, before and after the laser shots, the in-depth composition of tissue sections coated by a matrix for MALDI (Matrix-Assisted Laser Desorption-Ionisation) mass spectrometry imaging, in order to gain a better understanding of desorption-ionization phenomena involved in MALDI, particularly on tissue in the context of imaging. Then two work-packages are devoted to very different fields of science, in which an improvement of the capability of TOF-SIMS imaging is expected with 3-D analyses, or enhancement of the sensitivity, or even the possible cleaning of the sample surface without damaging it, when a sample is rare or unique. For each of these work-packages, informal collaborations have already been started since several years, and preliminary results or proof-of-concept have also been obtained. In the field of healthcare research, a first work-package will focus on the acquisition of ion images from samples of remodeled arteries selected in complex samples of explanted human lungs from patients suffering from pulmonary arterial hypertension, compared to controls, as well as from model rats, to help understanding of the pathophysiology of this incurable condition. Finally in the field of cultural heritage and archaeology, the last work package will study pigments from ancient painting samples, taken from paintings of artists dating from the Renaissance period to the twentieth century. The data will help to characterize the use and the mode of preparation of different pigments and binders: for example, the origin of the minerals, the nature of binders, the chemical synthesis of compounds, the mixing of different organic molecules. In each of these two applications, limitations of TOF-SIMS imaging have already been pointed, such as the intrinsic limitation of surface analysis, which will be lifted by the in-depth analysis, or the difficulty of obtaining clean surfaces, or the limited sensitivity which will now be increased. The final goal will be to make TOF-SIMS imaging a method of choice for micrometric localizedchemical analysis.