Electrokinetic-driven microfluidic system in poly(dimethylsiloxane) for mass spectrometry detection integrating sample injection, capillary electrophoresis, and electrospray emitter on-chip

Abstract

A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270 V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities.

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

“…This polypropylene tip is similar in geometry to many emitters that are molded directly into microfluidic devices [58][59][60][61][62][63][64][65]. The polypropylene substrate imparts a very hydrophobic surface to this emitter compared with the other emitters characterized in this study.…”

Trends in CE‐MS 2005–2006

“…The application of a separate emitter onto the chip is disadvantageous, because a high dead volume between the chip channel and the emitter is unavoidable and the application of a separate part is elaborate, which reduces the possibilities for mass production [8,9,13,14]. This leads to spray emitters, which are integrated in the chip and therefore made of the same bulk material than the chip.…”

“…Especially PDMS seems to have many advantageous properties and is applied in increasing numbers [8,9]. The problems of hydrophobic surface of the PDMS were overcome for example by in-channel oxidation [8]. The coating of the walls by a positively charged polymer, PolyE-323, shows good durability in long-term tests [9,10].…”

“…Polymer materials are gaining importance; polycarbonate, Zeonor, polyimide, poly(methyl methacrylate) (PMMA), SU-8 epoxy and poly(dimethylsiloxane) (PDMS) are applied for chip-based CE-MS [5,7]. Especially PDMS seems to have many advantageous properties and is applied in increasing numbers [8,9]. The problems of hydrophobic surface of the PDMS were overcome for example by in-channel oxidation [8].…”

“…25 (13), Electrophoresis 2005, vol. 26 (7)(8), Electrophoresis 2006, vol. 27 (11), and Electrophoresis 2007, vol.…”