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Methods for molecular analysis and imaging of solid surfaces are important for the development of materials science, biology and medical sciences. As an alternative to matrix-assisted laser desorption ionization (MALDI), we investigate the influence of a thin layer of gold (1-15 nm) condensed on the surface of a series of pure organic materials, without the use of a MALDI matrix, in the laser ablation using a 355 nm wavelength light. The evolution of the characteristic fragment ion intensities with increasing thickness of the gold overlayer has been recorded. For all the investigated materials, the largest signals of characteristic ions are measured after metallization with 4-8 nm of gold. The observed effects can be tentatively explained by the increased laser absorption by the gold nanoparticles in this wavelength range and, as suggested by surface potential measurements, by an increase of the ionization probability. Our results suggest that metal-assisted LDI provides an interesting alternative to MALDI for the surface analysis and, potentially, imaging of certain classes of materials, when a minimal perturbation of the surface structure is desired. The technique is not suitable to get high mass molecular signals in most cases, but intense signals of characteristic fragment ions are detected for all the tested samples. Because of the preservation of the sample surface and the controlled size of the gold islands ( |
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