New SPIN Corrals Protein Molecules
PNNL technology boosts mass spectrometer sensitivity and performance
Results: When studying the proteins in pre-cancerous or other cells, researchers don't have a lot of material—just the contents of a few cells. When they add a sample to the mass spectrometer, the workhorse of protein studies, they don't want to waste any. That's where SPIN comes in. Developed by a research team at Pacific Northwest National Laboratory, SPIN greatly increases the ability of mass spectrometers to analyze cell proteins and other extremely small samples.
Short for subambient pressure ionization with nanoelectrospray, SPIN gets more sample into a mass spectrometer. The increase in quantity yields more precise data because it enables researchers to examine more of the molecules in the sample.
Why it matters: The typical sample preparation method pulls proteins into the spectrometer through a very small opening. This process, known as electrospraying or ESI, takes place at standard atmospheric pressure in a chamber outside the mass spectrometer.
To obtain better analyses, researchers need to improve the sensitivity and other performance aspects of sample injection into mass spectrometer.
With SPIN, the electrospray takes place in a vacuum. By pulling in the molecules at a mere three percent of normal atmospheric pressure, researchers get far more of the sample into the instrument. Also, the SPIN source resides inside the mass spectrometer, which also reduces sample loss.
"Initial results show a promising five-fold increase in sensitivity," said principal investigator Jason Page. "Our ultimate goal is to have every molecule in the sample be ionized and transmitted to the mass spectrometer."
Methods: Researchers first focused on operating electrosprays at reduced pressures. Results from profiling the ions and charged droplets emitted from the electrospray source indicated that ESI can function efficiently in a vacuum of far less than the average atmospheric pressure.
Central to the success of the SPIN source was the use of electrodynamic ion funnels, another PNNL-developed technology. An ion funnel is a device with a large inlet that collects dispersed ions and directs them through a small aperture, with minimal sample losses.
The team had recently increased the working pressure of ion funnels to ~30 Torr, or 30 times lower than normal atmospheric pressure. The expanded pressure range of the ion funnel overlapped well with the lower end of the effective working pressures of the SPIN source.
"Combining the two technologies completely removed the large ion losses associated with the atmospheric sampling and increased the sensitivity of the spectrometer," Page said.
What's next? The scientists are working to increase the production of gas-phase ions from molecules in solution to match the already high transmission efficiency. They expect these advancements to position the SPIN source for other applications that require high sampling and detection efficiencies, such as single cell proteomics.
Acknowledgments: Members of the research team are Jason Page, Keqi Tang, Ryan Kelly and Richard D. Smith. At the Pacific Northwest National Laboratory, they advance scientific frontiers for U.S. innovation by achieving a predictive understanding of multicellular biological systems.
The work was conducted at the U.S. Department of Energy's EMSL, a scientific user facility located at PNNL. It was supported by the DOE Office of Biological and Environmental Research, the NIH National Center for Research Resources, the NIH National Cancer Institute, and the National Institute of Allergy and Infectious Diseases NIH/DHHS.
Reference: Page JS, K Tang, RT Kelly, and RD Smith. 2008. "A subambient pressure ionization with nanoelectrospray (SPIN) source and interface for improved sensitivity in mass spectrometry." Analytical Chemistry 80(5):1800-1805.