Novel 2D micronib ionization sources for nano electrospray-mass spectrometry (ESI-MS)

We present here novel 2D ´nib-like´ interfaces for nano-electro spray mass spectrometry (nanoESI-MS) applications. The design, fabrication and testing of three generations of such sources are outlined. The two first generations of nibs were fabricated using a negative photoresist (SU-8); they consisted of prototypes which allowed us to validate the idea of a nanoESI nib tip. They had respectively 20×30 μm and 8-16×35 μm section dimensions at their outlet. First generation nibs were seen not to have appropriate dimensions for nanoESI applications. Testing of the second generation demonstrated the influence of outlet orifice dimensions on the ionization process and on the electrospray performance. A third generation of micro-nibs was fabricated using polycrystalline silicon (poly-Si) and silicon-based surface micromachining techniques. These latter were highly planar and had much smaller tip dimensions of approximately 2×2 μm. MS testing on an ion trap mass spectrometer, with standard peptides initially, and then samples of various natures, showed the feasibility of the ´nib-like´ approach and the subsequent improvements obtained as the design and fabrication of the interfaces evolved.