Intact desorption and soft-landing of non-covalent complexes using ToF-SIMS

Nowadays, surfaces biofunctionalization is a subject of utmost interest, especially in medical and paramedical applications. Even if the immobilization of biomolecules from aqueous solutions has already shown efficiency, these methods suffer from negative aspects. Among others, the issues intrinsic to the drying process, such as the denaturation of the immobilized proteins, the limitation to monolayers and the poor control of spatial delivery, can reduce the achievable functions of the engineered biomaterials. Hence, researches and methods are increasingly being developed to counteract these drawbacks. This master thesis investigates the detection and transfer of non-covalent complexes, using small bismuth and large argon cluster ion beams, with a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The ultimate goal of this study is to succeed in the intact desorption from a surface and the soft-landing onto another without breaking weak interactions linking the two involved partners, in addition to covalent bonds. Two non-covalent systems have been studied in different conditions. These systems are, firstly, vancomycin, a glycopeptide antibiotic, which can specifically bind to small (acetyl-L-Lys-)D-Ala-D-Ala polypeptide and to itself by forming dimers and secondly, chromium trifluoroacetylacetonate (Cr(tfac)3 , i.e. more robust metallic complexes. Various parameters were tested: primary ion beam nature, cluster size and energy, sample thickness and substrate’s hardness which are among the most impactful ones. First, some reference analyses were achieved using Bi_5^+ and 〖Ar〗_(1500-3000-5000)^+ beams to (i) make sure these complexes could be detected (and so desorbed intact) by ToF-SIMS and (ii) to identify their mass spectral signature. Second, these non-covalent complexes were transferred using large 〖Ar〗_(3000-5000)^+ beams from a target, a silicon wafer on which high quantities of complexes have been deposited, onto a cleaned surface, the collector. These collectors were finally analyzed to assess if these complexes were transferred intact. A study on vancomycin fragmentation has also been achieved in function of the layer thickness, confirming previous theories and bringing additional information on ionization mechanisms of vancomycin pseudomolecular ions. Using optimized parameters, all complexes were successfully detected confirming that non-covalent complexes can be desorbed intact using ToF-SIMS. After being transferred, Cr(tfac)1-2 complexes were detected on the collectors in positive mode. For the vancomycin-ligand complexes and the vancomycin dimers, it resulted that these were too weakly bonded to allow detection after an additional ion impact compared to the analyses. Nevertheless, intact vancomycin molecules were transferred with a semi-circular deposition pattern confirming that large argon clusters, with their low energy per atom, significantly reduced the molecules fragmentation upon ion impacts.