Electrospray emitters silicon

Miniaturized LC/MS formats based on micromachined chip-based electrospray emitters and ionization sources on silicon (Schultz et al., 2000 Licklider et al., 2000 Ramsey and Ramsey 1997 Xue et al., 1997) and plastic (Vrouwe et al., 2000 Yuan and Shiea, 2001, Tang et al., 2001) microchips is a proactive approach for scale-down platforms. Various micromachining processes are used to fabricate these devices. These microanalytical technologies would create integrated sample preparation and LC/MS applications. The potential benefits of such a system include reduced consumption of sample/reagents, low cost, and disposability. 

Lee and co-workers demonstarted that a micromachined parylene nozzle could serve as an electrospray emitter on a silicon chip. This hollow-needle structure extended more than a millimeter beyond the edge of the silicon substrate. MS/MS analysis of the mixture of peptides obtained from the trypsin digest of cytochrome c was demonstrated with this micromachined emitter, and... 

Figure 5.9 Novel fabrication process for the second generation of micromachined electrospray emitter tips silicon support wafer (blue), 200 nm thick nickel etch-release layer (white) which is patterned using a HN03-based wet etch, negative photoresist SU-8 which forms the micro-nib support layer and tip which hosts the capillary slot (gold) and single photolithographic masking layer which defines the reservoir and tip (black).

On-Chip Electrospray, Fig. 6 Scanning electron microscopy images of an out-of-plane needle electrospray emitter tip fabricated at the bottom side of a liquid chamber etched into a silicon wafer. The view from the bottom is depicted in image (a) showing the 10 pm diameter needle protruding from the underside of the substrate. The view from the top of the substrate is depicted in image (b) showing the 600 pm liquid chamber (Reprinted with permission from [9])... 

Figure 5.8 Image of a nib emitter tip which is composed of a reservoir feature, a microchannel, a capillary slot and a point-like structure where electrospraying takes place. High voltage is applied on the silicon substrate which is in contact with the liquid in the reservoir and in the microchannel. (Adapted with permission from Ref. 15).

Electrospray ionization from microfluidic devices can be generated directly from the chip surface, from capillary emitters inserted in the chip, or from microfabricated emitters. Liquid sheath, liquid junction, and nano-ESI sources have been implemented on glass, polymeric, or silicon substrates. 

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