SURFACE MASS-SPECTROMETRY - APPLICATION TO BIOSENSOR CHARACTERIZATION

In order to allow a detailed control and specific tailoring of interfaces a surface analytical tool is required that localizes, identifies, and quantifies the molecular structures of interest. Surface mass spectrometry techniques (secondary ion mass spectrometry (SIMS) and laser postionization of sputtered neutrals (SNMS) as well as matrix assisted laser desorption (MALDI)) are such analytical tools. SIMS is the method of choice for a detailed characterization of the uppermost monolayer. With time-of-flight analysers (TOF-SIMS) elements as well as molecules up to 15,000 u can be identified with a sensitivity down to the ppb and fmol range, respectively. Larger molecules can be investigated by their characteristic fragments in so called fingerprint spectra. By rastering the ion beam across the surface ion images with a lateral resolution of <100 nm (elements) and about 1 mu m (molecules) can be obtained. The additional use of lasers for the postionization of sputtered neutrals (laser-SNMS) allows the quanitification of the results. By means of MALDI molecules up to several 100,000 u can be desorbed without fragmentation. In particular, proteins, saccharides and polymer molecules can uniquely be analyzed by this technique.