MALDI Microfluidics
From Murray Mass Spectrometry Group
Contents |
[edit] Overview
This project is aimed at developing an interface that allows microfluidic chip devices to be "read" by a mass spectrometer. Microfluidic chips are small devices with systems of micrometer sized channels etched into glass, silicon, or molded in plastic. The channels are enclosed by bonding to a flat substrate. Various microfluidic components have been developed to perform valving, mixing, filtering, electrophoresis, liquid chromatography, polymerase chain reaction and other procedures. Sample transport is typically by electroosmosis and/or electrophoresis. In analogy to electronic integrated circuits, multiple components can be combined to form microscale total analysis systems. The advantages of such devices compared to conventional chemical analysis include low cost, small size, low sample consumption, high sensitivity, and rapid analysis.
[edit] Group Members
Kermit Murray
Damien Narcisse
Jeonghoon Lee
Steve Soper
[edit] Research
[edit] On-line MALDI Chip
Rotating ball inlet closeup
The goal of this research is to develop an interface for coupling microfluidic chips directly to a matrix-assisted laser desorption/ionization (MALDI) mass spectrometer for on-line analysis. This chip-to-MALDI interface combines the advantages of microfluidic devices such as integrated nanoscale sample preparation, reaction, and separations with the advantages of MALDI MS detection, including excellent sensitivity, mass resolution, mass range, and speed of analysis. The interface is based on the rotating ball inlet configuration for MALDI developed in the Murray laboratory (Orsnes et al., 2000). A mechanically driven stainless steel ball delivers matrix and analyte from the chip, via capillary at atmospheric pressure, to the vacuum of the mass spectrometer. The interface allows for the ball, held at a high voltage, to simultaneously accelerate MALDI ions and be used as an electrode for electrophoresis. Standard crystalline MALDI matrices are used with a 355 nm Nd:YAG laser for desorption. In collaboration with Dr. Soper, novel chip configurations are being developed and constructed for the interface between the chip and the mass spectrometer and for on-chip analysis.
PMMA separation chip coupled to the ball inlet
The rotating ball inlet has been demonstrated with an on-line capillary electrophoresis separation and an article was published last year in Analytical Chemistry (Musyimi, et al., 2004). We have extended this work to couple a polymer microfluidic chip to a MALDI TOF mass spectrometer. Polymethyl methacrylate (PMMA) chips were microfabricated using hot embossing as the polymer replication technique with a molding die prepared using rapid prototyping micromilling techniques. A single linear separation channel is 50 µm wide, 100 µm deep and 8 cm effective length with a 10 nL offset T-injector was used to demonstrate a separation of a cytochrome C tryptic digest. The grayscale plot represents intensities of mass spectra (horizontal axis) during the separation (vertical axis). The tryptic peptides are visible as the numbered spots (see the attached article for additional details).
Having successfully demonstrated the on-line chip separation, we are now working to add further components to the microfluidic chip. The target device will include on-chip tryptic digestion and two dimensions of separation prior to on-line MALDI analysis.
[edit] Off-line IR LDI
The off-line part of the MALDI microfluidics project is centered on matrix-free soft laser desorption ionization from capillary gel microfluidic chips.
Schematic diagram of the functioning gel microfluidic chip ion source. The chip is shown below inset with buffer reservoir A, analyte reservoir B, analyte waste C and buffer waste D. Ions are desorbed from the chip held behind the target L0 and ions are accelerated into the flight tube by acceleration grids L1 and L2.
The most successful application of Infrared MALDI to date has been the matrix-free direct from gel soft IR laser desorption ionization. In article published last year in Analytical Chemistry, we demonstrated matrix-free soft IR-LDI in a standard size polyacrylamide gel (Xu, et al., 2004). This year, we have extended this approach to a capillary gel chip. The figure above shows a schematic diagram of this approach. The chip was fabricated from poly(methylmethacrylate) (PMMA) with a poly(dimethyl siloxane) (PDMS) cover. A sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gel separation was performed on the microfluidic chip. Ions were formed by irradiating the channel with 2.95 µm radiation from a pulsed OPO laser without the addition of matrix.
[edit] Presentations
[edit] Publications
- Musyimi, H. K.; Narcisse, D. A.; Zhang, X.; Stryjewski, W.; Soper, S. A.; Murray, K. K., Online CE-MALDI-TOF MS using a rotating ball interface Anal Chem 2004, 76, 5968.
- Xu, Y.; Little, M. W.; Rousell, D. J.; Laboy, J. L.; Murray, K. K., Direct from polyacrylamide gel infrared laser desorption/ionization. Anal Chem 2004, 76, 1078.
- Zhang, X.; Narcisse, D. A.; Murray, K. K., On-line single droplet deposition for MALDI mass spectrometry. J Am Soc Mass Spectrom 2004, 15, 1471.
- Orsnes, H.; Graf, T.; Degn, H.; Murray, K. K., A Rotating Ball Inlet for On-Line MALDI Mass Spectrometry. Anal. Chem. 2000, 72, 251.
