Electrospray Device Fabrication

Parylene C was chosen to fabricate the triangular electrosprayer tip because it was easy to deposit and could be patterned using photolithography and plasma etching. In addition, its resistance to most organic solvent makes it suitable for electrospray applications. Other materials of similar structure should have comparable properties. 

The fabrication procedure for the parylene electro spray tip is relatively simple, but manual alignment of the parylene tip to the end of the microchannel is tedious and should be replaced by a structure with mechanical alignment features. Because the thermal parameters of parylene are different from those of the cyclo-olefin polymer substrate, good control of the thermal bonding conditions is required for proper sealing between two materials without collapsing of the microchannels. 

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Huikko, K., Ostman, P., Grigoras, K., Tuomikoski, S., Tiainen, V.M., Soininen, A., Puolanne, K., Manz, A., Franssila, S., Kostiainen, R., Kotiaho, T., Poly(dimethylsiloxane) electrospray devices fabricated with diamond-like car-bon-poly(dimethylsiloxane) coated SU-8 masters. Labchip 2003, 3, 67-72. 

FIGURE 41.7 Examples of electrospray devices fabricated in PT. (a) A drop of KCl solution at the channel outlet and (b) electrospray tip with Taylor s cone generated by electrostatic field. (Reprinted from do Lago, C.L., et al, Anal. Chem., 75, 3853, 2003. With permission.)... 

The fabrication procedure for the two-tip device is basically the same as the single electrospray device. First, the two independent microchannels were hot embossed onto one cyclo-olefin polymer chip, and the two sample reservoir holes were drilled onto this cyclo-olefin chip at the end of the microchannels. Then, a gold electrode with a width of 500 pm was fabricated onto another cyclo-olefin chip. A hole for gold electrode access was drilled through the other... 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

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. 

FIGURE 7.35 (a) Initial mass spectrum obtained from PMMA microchip device. The mass spectrum is characterized by a substantial chemical noise background most likely due to residual developer solution present in the microchannels, (b) Electrospray mass spectrum obtained with 10 pM angiotensin I (in 50 50 MeOH/H20 containing 1% acetic acid) after the PMMA microchip has been washed with 50 50 MeOH/H20. The simple solvent wash completely eliminates the residual chemical contamination arising from the microchip fabrication step [200]. Reprinted with permission from the American Chemical Society. 

Wen, J., Lin, Y.H., Xiang, F., Matson, D.W., Udseth, H.R., Smith, R.D., Micro-fabricated isoelectric focusing device for direct electrospray ionization-mass spectrometry. Electrophoresis 2000, 21, 191-197. 

The formation of a porous structure results from phase separation (or phase inversion) mechanisms that are not limited to electrospraying. It is the process that controls membrane formation, as the solvent exchanges with a nonsolvent, polymer solution solidifies and polymeric device forms. The phase separation is fully investigated in fabrication of flat or hollow fiber membranes or in situ forming drug delivery systems. - Usually, quick evaporation of the solvent produces particles with porous or golf ball-shaped surfaces (Figure 22.26). 

Dye sensitized solar cells built without any transparent metal oxide electrodes (ITO or FTO) were presented recently by Kashiwa et The layout of the device is shown in Figure 11. To fabricate such device, titanium dioxide paste was coated directly on a glass substrate. On the top of Ti02 layer, tetrapode-shaped nanocrystals of zinc oxide were deposited by electrospray technique. A layer of metal titanium was sputtered on the top. Following etching of the zinc oxide template produced pores in the titanium layer. 

A third strategy for microfluidic-nanospray interfaces, microfahricated, tapered electrospray tips [8-12] is the most promising that has been reported. In fact, several devices with this configuration are now available commercially (for example, from Advion Biosciences and Agilent Laboratories). Several authors have fabricated devices capable of sustaining a stable spray with no dead volume between the channel and tip. For example. Fig. 2a shows a micro-milled electrospray nozzle in poly(methyl... 

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