Special Surfaces to Mimic the Matrix

Example DIOS-TOF/TOF experiments on the tryptic digest of 100 fmol of the protein bovine serum albumine (BSA) demonstrate this technique. Using conductive tape the DIOS chip was directly attached to the MALDI target plate of an Applied Biosystems 4700 tandem TOF instrument equipped with a frequency-tripled Nd YAG laser (355 nm). The resulting DIOS-TOF spectmm of the digest and the DIOS-TOF/TOF spectrum of one selected peptide, [YLYEIAR+H] , m/z 927.5 are shown in Fig. 11.27. The tandem mass spectrum provides complete detection of the y and b ion series [192]. 

A more recent approach, also from the Suizdak group, is to modify silicon surfaces with single-crystal silicon nanowires (SiNWs), which also happen to provide a good platform for surface-based mass spectrometry. Those silicon nanowires are directly synthesized on the surface of a silicon wafer. The formation of SiNW can be well controlled to define physical dimensions, composition, density, and position of the nanowires on the surface [193,194]. 

The synthesis of SiNWs starts from gold nanoparticles with diameters of 10, 20, or 40 nm that are distributed on a silicon substrate. The nanoclusters are required to catalyze SiNW growth. The method employs an elaborate series of steps of growth, etching, oxidation, and finally silylation to generate a perfluorophenyl- 

The term nano-assisted laser desorption/ionization (NALDI) [195,196] has been coined for techniques using nanostructured surfaces to mimic MALDI. NALDI sample plates are commerically available from a major manufacturer of MALDI-TOF instrumentation (Fig. 11.28). Like DIOS, NALDI is particularly useful for small molecule analysis in high-throughput analytics [195,195,196]. 

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