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Femtomolar sensitivity with matrix-free LDI MS layer, says Matthias Rainer, another The researchers also detected pepScientists who want to analyze small group member. “Their electrical, thertides that fall into the same mass range molecules with MALDI MS have long mal, and optical properties improve the as vaporized matrix would and successbeen frustrated by unwelcome signals efficiency of laser transfer, leading to fully measured the m/z of peptides in a from the matrix. And until now, matrixhigh reproducibility.” BSA digest, an amino acid, a phosphofree LDI has not reached the femtomolipid, and an emulsifier lar sensitivity required to, found in the small intestine. for example, perform cliniThe masses of these test cal blood tests for metabocompounds ranged from lites. But Gu¨nther Bonn 100 to 1500 Da. “The difand colleagues at Leopoldferent analytes reported Franzens University (Aushere show the broader aptria) report in a new AC plication of DLC,” Rainer paper (DOI 10.1021/ says. “This is important, as ac801190e) that they have many matrix-free systems boosted sensitivity into the are reported to be viable for femtomolar range by replaca fixed kind of analyte.” ing their MALDI target The group is trying to with a DVD coated with increase sensitivity even furdiamond-like carbon ther by decreasing the (DLC). “That it worked (a) The matrix-free target is a polycarbonate DVD coated with an interlayer of thickness of the DLC layer was really a surprise,” says molybdenum and topped with a layer of DLC. Even after the DVD is coated, it Bonn, who hopes to use the can store data. (b) A laser pulse desorbs and ionizes the sample from the car- and chemically modifying its surface. For example, technology to create metab- bon layer for analysis by MS. they are applying aromatic olomic tests for prostate Bonn wanted to use DVDs so he compounds, such as sinapinic acid, to cancer. could burn analytical data onto their boost UV sensitivity and thereby expand The porous silicon most commonly undersides. This technique is particularly the mass range. Before the technology used as a target for matrix-free LDI is easuseful, he points out, when hundreds of can be commercialized, they must also ily contaminated and can’t be stored for samples are processed at the same time, test its reproducibility in different labs longer than a year. But DLC coatings because each sample remains physically and see whether it can be used with difdon’t age quickly and are flexible, amorconnected to its spectrometric data. ferent MALDI machines because, to phous, and hard as diamond. ManufacAn adapter is needed to insert the date, measurements have been made tured from graphite, they’re used to exDLC DVD into a mass spectrometer, only with a Bruker Daltonics Ultraflex tend the life of metals in razor blades, drill and a small magnet holds the target in mass spectrometer. bits, and many other products. place. To begin the analysis, up to 100 But what they’d really like to do, To make the matrix-free target, Bonn’s group first sputters molybdenum 1 L spots are pipetted onto the target’s Bonn says, is use their new technology to find low-molecular-weight biomarkonto 1.4 GB polycarbonate DVDs, surface. “The laser can be shot at any ers. In collaboration with clinicians at which resemble, but are smaller than, area within the boundary of the analyte Innsbruck Medical University (Austria), the storage disks for video cameras. The spot,” Rainer says. “So every spot is a Bonn is searching for small molecules in thin (⬃30 nm) metal layer seals the sweet spot on the DLC-coated target.” the blood that could be used to diagDVD, preventing interference from the Because Bonn and his group are parnose and stage prostate cancer. The polycarbonate, and also dissipates the ticularly interested in carbohydrate meprostate-specific antigen test (the curlaser beam over the disk’s surface, pertabolism, they wanted to determine rent gold standard) “gives a selectivity of mitting less energy to be used. A rough whether the new technology could approximately 30%,” he says. “With the layer (⬃300 nm) of DLC is then deposquantify monosaccharides. L-Sorbose metabolomic approach and our disk ited on top of the molybdenum by a (1 nmol/L) produced sharp peaks at technology, we expect higher sensitivity pulsed laser. The top layer’s 10⫺12% 203.04 m/z (the sodium adduct) and and selectivity.” hydrogen content makes it hydrophobic 219.05 m/z (the potassium adduct). —Linda Sage enough to hold samples. “Also, the LDI Lactulose was also easily detectable, and potential is enormously enhanced by the even peaks for sodium and potassium submicrometer structures” in the carbon ions were visible. 10.1021/AC801668W 2008 AMERICAN CHEMICAL SOCIETY
Published on Web 08/29/2008
OCTOBER 1, 2008 / ANALYTICAL CHEMISTRY
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