NEW YORK – Sample separation firm Mobilion Systems is applying its SLIM (structures for lossless ion manipulation) ion mobility technology to proteomics.
According to the Chadds Ford, Pennsylvania-based company, its SLIM technology could allow researchers to conduct mass spec-based proteomics experiments without quadrupole filtering, which could improve the speed and sensitivity of such analyses.
Ion mobility uses differences in size, shape, and charge to separate ions in the gas phase. Mass spec vendors including Waters, Agilent, Sciex, Thermo Fisher Scientific, and Bruker offer instruments incorporating IMS devices, which proteomics researchers typically use to provide an additional layer of separation after conventional LC.
SLIM ion mobility extends ion mobility path lengths beyond that allowed by conventional IMS systems, enabling much more extensive separations. The technology uses arrays of printed electrodes to confine ions within the ion mobility field. This makes it possible to route ions around turns without losses, meaning that an IMS drift path can be designed to run along a serpentine path, greatly increasing the length of the IMS path without increasing the footprint of the device.
SLIM technology was developed by researchers at Pacific Northwest National Laboratory (PNNL) and licensed by Mobilion. To date, the company has largely marketed the technology for targeted analyses in areas like biopharma where it has been used for applications like peptide mapping and monitoring of protein post-translational modifications.
Mobilion now plans to tackle the proteomics market, where CEO Melissa Sherman said it could substantially boost the performance of mass spec workflows.
The company has been working to apply the SLIM technology to proteomics for seven years, Sherman said. "It has kind of been our Holy Grail, which we haven't talked about but have been working towards."
In a typical mass spec proteomics experiment, precursor ions with a particular mass-to-charge ratio (m/z) are selected for fragmentation using the instrument's quadrupole, and the fragment ions produced are then analyzed to collect MS/MS level data. This initial selection step simplifies the sample so that high-quality data can be collected on the subset of precursors selected for fragmentation.
However, any precursor ions not selected for fragmentation are discarded. This means the number of ions analyzed is only a small proportion of the total ions initially introduced into the mass spectrometer, which negatively impacts the sensitivity of the experiment, particularly where low-abundance analytes are concerned. According to a white paper Mobilion released detailing its plans to move into proteomics, mass spec proteomics experiments commonly use only between 1 percent and 20 percent of the total available ions.
The company is positioning its SLIM technology as a tool that will eliminate the need for quadrupole filtering of precursor ions. Instead, in a workflow the company has termed parallel accumulation with mobility aligned fragmentation (PAMAF), the SLIM system will provide ion mobility separation with high-enough resolution that the mass spec can fragment and analyze essentially the full available ion signal.
"We are using [SLIM] to separate all the ions so we don't have to throw anything away," Sherman said.
Eliminating quadrupole filtering also increases the speed of the instrument, Sherman said. "We get the double bonus of increased sensitivity and faster analysis times."
She said Mobilion projects the PAMAF approach will deliver a fivefold improvement in speed and a tenfold improvement in signal-to-noise compared to existing workflows on the latest instrumentation.
Richard Smith, one of the developers of the SLIM technology and formerly the director of proteomics research at PNNL, noted as another advantage the ability of the system to collect large populations of ions and then deliver them to the mass spec in dense, separated ion mobility peaks.
"If your [ion] accumulation time is 100 milliseconds and you compress the ions of a given type so that when they get to the [mass] detector they are in a peak that is only a millisecond wide, that corresponds to roughly a two-orders-of-magnitude increase in the ion density getting to the mass spectrometer at any given time," Smith said. "There's a huge gain that comes from that."
In a 2020 Analytical Chemistry paper, Smith and colleagues demonstrated a SLIM-based mass spec workflow that achieved greater than 98 percent ion utilization.
He suggested that advances on the informatics side could further boost the technology's utility. He said that while vendors like Bruker and Waters have "done a good job with a lot of the tools using ion mobility … there is a ways to go to really squeeze the most information out of the [ion mobility] separations."
Smith said he envisions broad application of the technology in proteomics research.
"I think it should become something that is used for everything," he said. "I see no downside."
He added that the proteomic workflows described in the Mobilion white paper "were absolutely in our thinking from the beginning."
Others have also contemplated using SLIM for proteomics. Jesse Meyer, assistant professor at Cedars Sinai, has discussed potentially using the technology as part of direct-infusion mass spec workflows his lab has been developing. In a commentary published in the Journal of Proteome Research in May, Meyer and coauthors including several Mobilion researchers raised the possibility that improvements in IMS technologies like SLIM could eliminate the need for liquid chromatography in some proteomics experiments.
Sherman said Mobilion also plans to target the system to researchers in areas like lipidomics and metabolomics, where she said its ability to resolve chimeric spectra produced by isomeric and isobaric compounds could prove attractive.
Sherman said the company has prototypes of the system up and running internally but does not yet have a timeline for when it might deploy these prototypes in outside labs. The company plans in coming weeks to begin giving leading proteomics researchers access to its internal prototypes with the intention of collaborating on the technology and method development.
"Our approach is to bring KOLs to our lab and have them work together side by side and run samples and collect data," she said. "Our KOLs will be working with us and the different vendors we are working with, and they will be helping us evolve and improve along the way."
Sherman said the system will be compatible with QTOFs from all leading mass spec vendors. She also raised the possibility that Mobilion would have an original equipment manufacturer produce TOF or QTOF instruments it could sell for use with the system.
In 2018, Mobilion partnered with Agilent Technologies to integrate SLIM technology into the company's 6500 line of QTOFs. Last year, it sublicensed the technology to Swiss mass spec firm Tofwerk, allowing that company to incorporate SLIM technology into a TOF instrument intended for analysis of volatile organic compounds.
In the white paper, Mobilion researchers generated proof-of-concept proteomics data on a modified Agilent 6546 QTOF.