Fully Microfabricated and Integrated SU-8-Based Capillary Electrophoresis-Electrospray Ionization Microchips for Mass Spectrometry

Abstract

We present a fully microfabricated and monolithically integrated capillary electrophoresis (CE)-electrospray ionization (ESI) chip for coupling with high-throughput mass spectrometric (MS) analysis. The chips are fabricated fully of a negative photoresist SU-8 by a standard lithographic process which enables straightforward batch fabrication of multiple chips with precisely controlled dimensions and, thus, reproducible analytical performance from chip to chip. As the coaxial sheath flow interface is patterned as an integral part of the SU-8 chip, the fluidic design is dead-volume-free. No significant peak broadening occurs so that very narrow peak widths (down to 2-3 s) are obtained. The sheath flow interface also enables comprehensive optimization of both the CE and the ESI conditions separately so that the same chip design is adaptable to diverse analytical conditions. Plate numbers of the order of 105 m-1 and good resolution are routinely reached for small molecules and peptides within a 2 cm separation length and a typical cycle time of only 30-90 s per sample. In addition, a limit of detection of 100 nM corresponding to a total amount of only 4.5 amol (per injection volume of 45 pL) and excellent quantitative linearity (R2 = 0.9999; 100 nM to 100 microM) were obtained in small-molecule analysis using verapamil as a test compound. The quantitative repeatability was proven good (8.5-21.4% relative standard deviation, peak area) also for the other drug substances and peptides tested.

Dynamic coating of SU‐8 microfluidic chips with phospholipid disks

“…SU-8 was chosen as the microchip fabrication material because of its favorable chemical stability and manifold patterning possibilities by UV-lithographic and bonding techniques [25]. SU-8 has been utilized not only in microelectromechanical systems [26] but also as structural material in many miniaturized (total) analysis systems, such as microchip-based CE [27,28], LC [29], and ESI/MS [30][31][32][33]. The use of SU-8 in bio-microelectromechanical system applications has also gained a lot of interest recently.…”

Recent advances in microfluidic technologies for biochemistry and molecular biology

“…In recent years, a range of microfluidic tools for performing efficient protein analysis have been reported. For example, protein crystallization (22)(23)(24)(25), protein-protein interactions (26)(27)(28), and two-dimensional gel electrophoresis (29,30) have been realised within planar-chip formats.…”

“…Advantages of performing electrophoresis on the microscale include improved analytical performance (with respect to both efficiency and resolution), lower sample consumption, system portability, and ultra-short analysis times. In addition, it is simple to integrate capillary electrophoresis with both up-stream and down-stream components such as post column reactors and mass spectroscopic analysis (30). For example, a monolithically integrated capillary electrophoresis-electrospraying ionization microchip was reported by Sikanen et al to allow mass spectrometric analysis of small molecules and peptides (30).…”

“…In addition, it is simple to integrate capillary electrophoresis with both up-stream and down-stream components such as post column reactors and mass spectroscopic analysis (30). For example, a monolithically integrated capillary electrophoresis-electrospraying ionization microchip was reported by Sikanen et al to allow mass spectrometric analysis of small molecules and peptides (30). Free flow electrophoresis is a continuous separation technique that utilizes hydrodynamic flow and an applied electric field perpendicular to the flow to separate analytes in flowing streams (54).…”

Microchip technology in mass spectrometry

“…In addition LC, microfabricated emitters have been coupled to on-chip electrophoretic separation compartments (Zhang et al, 1999;Wen et al, 2000;Dahlin et al, 2005b;Thorslund et al, 2005;Hoffmann et al, 2007;Sikanen et al, 2007). Electrophoretic separation is based on electromigration under a high electric field, and the sample injection is typically performed on-chip, which enables minimal delay time and rapid analyses as compared with LC (see, e.g., Fig.…”