A Micromachined Chip-Based Electrospray Source for Mass Spectrometry

Abstract

A micromachining process is described for fabricating a mass spectrometry electrospray source on a silicon chip. The process utilizes polymer (parylene) layers to form a system of chambers, filters, channels, and hollow needle structures (electrospray emitters) that extend more than a millimeter beyond the edge of the silicon substrate. The use of photoresist as the sacrificial layer facilitates the creation of long channels. Access to the channel structures on the chip is through a port etched through the silicon substrate that also serves as a sample reservoir. A reusable chip holder consisting of two plastic plates and an elastomer gasket provides the means to mount the chip in front of the mass spectrometer inlet and make electrical and gas connections. The electrospray emitters have tapered tips with 5 microns x 10 microns rectangular openings. The shape of the tip can be varied depending on the shape of the mask used to protect the parylene structures during the final plasma etch. The parylene emitters are physically robust and require only a high electric field to achieve stable electrospray operation over a period of a few hours. Direct comparisons with conventional glass or fused silica emitters indicated very similar performance with respect to signal strength and stability, spectral quality, and endurance. The automated MS/MS analysis of a mixture of tryptic peptides was no more difficult and yielded nearly identical results as the analysis of the same sample using a conventional nanospray device. This work demonstrates that an efficient electrospray interface to mass spectrometry can be integrated with other on-chip structures and mass-produced using a batch process.

Plane model of fluid interface rupture in an electric field

“…27 The model presented here is of particular importance to miniaturized electrospray emitters. Ramsey and Ramsey, 28 Licklider et al, 29 Le Gac et al, 30 and Bedair and Oleschuk 31 all report microscale emitters, often coupled with microfluidic channel networks, used in mass spectrometry. Improved design decisions for the emitters can be made if the conditions ͑based on the defined parameters͒ required for an electrospray can be predicted.…”

Analytical Performance of a Venturi-Assisted Array of Micromachined Ultrasonic Electrosprays Coupled to Ion Trap Mass Spectrometry for the Analysis of Peptides and Proteins

“…Reported miniaturized nanospray infusion devices fall into three main categories: (1) devices using fused silica capillary emitters attached to a chip 14-21 , (2) devices using a microchannel exiting the edge of a wafer 22-29 , and (3) monolithic devices using etched ESI tips [30][31][32][33][34][35][36] . Integrated miniaturized nanoESI devices comprising enrichment columns, reverse-phase separation channels and micromachined nanospray emitters have also been recently reported [37][38][39] .…”

Integration of a flow-type chemiluminescence detector on a glass electrophoresis chip

“…However, to realize miniaturization and integration of lab-on-a-chip devices, it is indispensible to employ equally miniaturized detectors. Up to now, laser-induced fluorescence (LIF) [9,10] and mass spectroscopy (MS) [11,12] have been most often utilized for -TAS detection because of their high sensitivity. Although submicromolar detectability can be readily obtained with these two types of detectors, the high cost and large size of the instruments are quite incompatible with the concept of -TAS.…”