Fluorinated surfaces: towards a universal matrix-free substrates for Laser Desorption Ionization

Matrix Assisted Laser Desorption Ionization (MALDI) is a soft ionization method that finds widespread applications in high-throughput mass spectrometric analysis. One of the main limit of this technique is that it requires the use of matrices: these molecules enable the analytes desorption and ionization (D/I) processes but also generate strong interfering signals in the low mass spectral region, preventing a suitable detection of low molecular weight compounds. The possibility to avoid their use will ease both sample preparation and mass spectrum (MS) interpretation. In recent years nanostructured surfaces have been proposed as a viable method to achieve such goal but the results are limited to specific classes of chemical compounds and the approach lacks in generality. Here we demonstrate that the fluorination of surfaces is the only step needed to activate the target and to achieve matrix-free operation with the same detection limit obtained using nanostructured chips. The results of this work suggest that D/I is a purely interfacial effect, with negligible contribution from chemical nature of the underlying substrate, provided that the substrate is conductive and able to efficiently absorb the UV laser beam.