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Purdue Researchers Adapt Miniature Mass Spec for Peptide Quantitation


NEW YORK – A team led by researchers at China's Tsinghua University and Purdue University has developed a miniature mass spectrometry capable of targeted peptide quantitation.

Detailed in a study published last month in the Journal of Proteome Research, the instrument could allow for applications like point-of-care analysis of peptide or protein biomarkers, said Zheng Ouyang, a professor at Tsinghua and Purdue and senior author on the paper.

Ouyang is also the president and founder of Purspec Technologies, a miniature mass spec company he launched in 2015 to commercialize technology developed in collaboration with his Purdue colleague Graham Cooks.

While Purspec's miniature mass spec business has focused largely on applications like drug and food safety testing and product authentication, the ability to make peptide and protein measurements could help it move into life science applications. Ouyang said the company is currently working with Indiana University Medical Center and a hospital in Shanghai on using its mini mass specs for point-of-care measurements of a biomarker used to guide glioma surgery.

While proteomics research in particular and life science research more broadly is still dominated by high-end instrumentation, in recent years more streamlined and portable mass specs have been explored for applications like point-of-care testing and in-surgery analysis.

Much of this work has focused on the use of ambient ionization approaches, like desorption electrospray ionization (DESI) or paper spray ionization that allow users to avoid conventional liquid chromatography, simplifying the upfront portions of mass spec workflows. A few companies, like Purspec and Boston-based 908 Devices, however, have focused on shrinking the mass spec instrument itself.

Ouyang noted that even before the work presented in the JPR study, Purspec's mini mass spectrometers had m/z ranges sufficient for measuring biomolecules like peptides. He said that the main reason the company hadn't pursued peptide work was the complexity of the sample prep required for protein analysis.

"We were directing the mini mass spec towards clinical point-of-care work instead of being in the lab," he said. "That meant that you wanted the sample [prep] to be simple. That was the problem with peptide and protein [analysis]. With proteins you had to do digestion, you have to do pre-concentration [of target peptides]. So that was what blocked that application of the mini mass spec."

Ouyang said he was convinced to pursue peptide quantitation by researchers at Cell Signaling Technology (CST), a Danvers, Massachusetts-based provider of research and diagnostic reagents.

The company, three employees from which also contributed to the JPR paper, told Ouyang that it thought mini mass specs could prove useful for peptide quantitation in combination with automated protein digestion and enrichment processes it was developing.

In the study, the researchers used the mini mass spec to quantify levels of the Met protein, a tyrosine kinase receptor that has been linked to poor patient outcomes in cancer. Using isotope-labeled Met peptides, they found that they could measure the peptides with good linearity at concentrations ranging from 50 nM to 5 μM with a limit of detection of 10 nM and a limit of quantitation of 20 nM.

They also tested the approach in cell lysate, using the human breast cancer cell line SKBR3, using anti-Met antibodies to isolate the target peptides from this sample and the mini mass spec to determine that Met peptide was present in the cells at a concentration of 125 nM, indicating that targeted quantitation of peptides in biological samples was feasible at the nanomolar level.

Ouyang noted that while the existing Purspec instruments were in theory capable of peptide analysis, he and his colleagues made a number of modifications to improve their performance.

One significant modification was the addition of a second ion trap, which Ouyang said was key to increasing the instrument's duty cycle.

He said that one of the strategies he and his colleagues relied on to miniaturize the mass spec was the use of a discontinuous atmospheric pressure interface, which reduces the size of the pumping systems required to move ions throughout the machine. This requires the instrument to ramp up the instrument pressure after the introduction of sample, which adds time to the duty cycle.

By adding a second ion trap, the researchers are able to introduce the sample into the first trap, ramp up pressure and then do MS/MS analysis continuously in the second ion trap, which speeds the duty cycle and boosts performance.

Additionally, the second trap lets users control isolation and collision-induced dissociation of ions in a way that allows for selection of ions in a manner similar to a triple quadrupole instrument, Ouyang said.

He said the work was intended as a proof of concept but added that he did see commercial potential for the dual trap device as it improved the duty cycle and quantitative capability of the instrument. He said adding the second trap did not require changing the size or form of the original system. The instrument measures roughly one foot by one foot by two feet, weighs around 40 pounds, and can be operated off a standard electrical outlet.

Purspec has begun moving into the life science space with its original instrument, called the Mini β, working with researchers at Indiana University Medical Center and in Shanghai measuring the metabolite two-hydroxyglutarate (2HG) during glioma surgery.

Different levels of 2HG correlate with different glioma types, with different types calling for different surgical plans, Ouyang said. Currently, traditional pathology is used to assess 2HG levels, a process that can take several hours during which time the patient is still in surgery. Ouyang said the hope is that using a Mini β in the surgical suite, results can be available in a matter of minutes.