Abstract
Monolithically integrated emitters have been increasingly applied to microfluidic devices that are coupled to mass spectrometers (MS) as electrospray ionization sources (ESI). A new method was developed to fabricate a duplicable structure which integrated the emitter into a poly(dimethylsiloxane) chip corner. Two photoresist layers containing a raised base which guaranteed the precise integration of the electrospray tip emitter and ensured that the cutting out of the tip exerted no influence even during repeated prototyping were used to ease the operation of the process. Highly stable ESI-MS performance was obtained and the results were compared with those of a commercial fused-silica capillary source. Furthermore, chip-to-chip and run-to-run results indicated both reliability and reproducibility during repeated fabrication. These results reveal that the proposed chip can provide an ideal ion source for MS across many applications, especially with the perspective to be widely used in portable MS during on-site analysis.
Highlights
Micro-fabricated devices have proven highly advantageous for manipulating small sample volumes, integrating complex and diverse sample pre-treatments and separations, and coupling with other rapid detection methods
The technology used in this work ensured that the end could already be blunt in the micro-channel contained layer and the 180 μm thickness raised layer when de-moulded, and that the cuts only needed to be applied to the substrate layer without impacting the vulnerable channel
In the fabrication procedure of these ends, a raised base was formed in the lithography process and three manual cuts with a razor were needed for the substrate layer
Summary
Micro-fabricated devices have proven highly advantageous for manipulating small sample volumes, integrating complex and diverse sample pre-treatments and separations, and coupling with other rapid detection methods. Integrated with pre-treatment modules and coupled with a mass spectrometer (MS), microfluidic chips can be applied in various kinds of quantitative analysis, such as biological, environmental, food safety and so on [1,2,3,4]. Several approaches to interface the microchips with an electrospray ionization mass spectrometer (ESI-MS) have been proposed [5]. The early approach emerging during the last decade was to fabricate open micro-channels directly at the edge of the chip. The second approach which involved inserting the fused-silica capillaries directly into the ends of the channels was technically difficult to realize. The integrated emitters were mainly based on hard materials such as glass and silicon [6,7,8,9,10,11,12,13], so that the fabrication process for a single emitter base, given the required processes of lithography and etching, were always complicated, time-consuming, and expensive
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