Fabrication of Si Templates for the Construction of Monolithic Multi-Electrospray Emitters
EMSL Project ID
17502
Abstract
Electrospray ionization (ESI) has made possible the online coupling of chemical separation techniques such as liquid chromatography with mass spectrometry (MS) for the analysis of large biomolecules (e.g., proteins). While the detection limits attainable using ESI-MS are sufficient for many applications, further decreases in detection limits would make possible the identification of currently unobservable trace biological compounds. For ESI, analyte solution is pumped through a capillary to an outlet, where it is subjected to a high voltage, causing charged droplets to be ejected from a so-called Taylor cone. Typically, the total number of ions produced in the ESI process is limited by the maximum current that can be sustained by a single Taylor cone. To increase the ion current, it is necessary to generate electrospray from multiple Taylor cones simultaneously.
We propose an approach to microfabricate ESI emitters that will facilitate the formation of multiple Taylor cones, and which will be supplied with analyte solution from a single capillary. The EMSL clean room will be used to photolithographically pattern and chemically etch silicon substrates, which will serve as templates for the construction of the multi-ESI emitters. Single crystal <100> Si wafers will have an array of squares patterned on the surface using standard photolithographic processing techniques that are readily available in the EMSL clean room. Taking advantage of the crystallinity of the silicon, the wafers will be anisotropically etched in a heated aqueous KOH solution, which will result in a template having inverted pyramidal features.
After etching, the templates will be taken from the clean room facility to our laboratory space, and a porous monolithic material will be cast onto the patterned wafers. Both silica-based and polymeric monolithic materials will be evaluated. The patterned monolithic emitters will then be removed from the mold and interfaced with a capillary. When the ESI voltage is applied, the electric field will be greatest at the ends of the protruding pyramidal features, and a Taylor cone should form at each. This straightforward approach to creating multi-electrospray emitters should provide a significant advance to the field of ESI-MS, resulting in a significant enhancement in analytical sensitivity.
Project Details
Project type
Exploratory Research
Start Date
2006-01-19
End Date
2007-01-13
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Kelly RT, JS Page, I Marginean, K Tang, and RD Smith. 2009. "Dilution-Free Analysis from Picoliter Droplets by Nano-Electrospray Ionization Mass Spectrometry." Angewandte Chemie International Edition 48(37):6832-6835. doi:10.1002/anie.200902501