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MASS SPECTROMETRY
Friction powers mass spec ionization Charge generated by rubbing materials together ionizes tiny samples If you’ve ever rubbed a balloon against your head to make your hair stand on end, you’ve experienced triboelectricity. Researchers at Georgia Tech are now putting such electricity—which is really just an electric charge generated by friction—to good use: They’re using triboelectricity to drive the ionization of molecules in a mass spectrometer. Materials scientist Zhong Lin Wang, mass spectrometrist Facundo M. Fernández, and coworkers replace the high-voltage power supplies that usually drive ionization with devices called triboelectric nanogenerators, or TENGs (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2017.17). These TENGs consist of a pair of electrodes and at least one pair of triboelectric layers, which are made of copper films on a polymer support. Movement of the layers relative to one another generates a charge that flows through the electrodes to an external circuit that includes a nanoelectrospray emitter. The layers’ surface area dictates the amount of charge generated. In the nanoelectrospray emitter, the charge
With these devices, no external power supply is needed for ionization. “You can literally rub the two surfaces together by hand, and that’s enough to produce charges to ionize molecules,” Fernández says. “Ionization methods in mass spectrometry are notoriously wasteful of the sample and produced ions,” says Akos Vertes, a chemistry professor at George Washington University. Sliding two triboelectric layers across each Conventional methods often other generates a charge that can power a produce ions that don’t make it nanoelectrospray ion source. into the mass analyzer. Fernández and coworkers “have created fraction of the charge going into generating a simple method for the on-demand generions and less charge being wasted than with ation of a predetermined amount of ions,” a conventional power supply. Vertes says. “The ability to control the That sensitivity makes the source ideal amount of ions per pulse is an important for working with tiny sample volumes. advantage for efficient detection and analy- “This is a great ion source if you have very sis by a variety of mass spectrometers. This precious samples,” he says. “You don’t want efficiency translates into superb sensitivity to consume the whole sample to perform for a broad variety of samples.” your analysis.” In addition to being small and sensitive, the source is also inexpensive. “It’s probably the cheapest ion source you can think of,” Fernández says. “You can literally build these for less than $2.00.” —Facundo M. Fernández, mass spectrometrist, Georgia Tech Renato Zenobi, a chemistry professor at ETH Zurich who studies ionization ionizes molecules as droplets are generated In fact, the TENG-powered nanoelecmethods, suggests that such devices could from the sample solution. trospray source is more sensitive than a be used with portable or handheld mass The researchers made TENGs in two conventional nanoelectrospray source. For spectrometers. configurations. In one, the layers slide example, with the TENG, the researchers Fernández plans to use the source to anacross each other. In the other, the layers were able to detect 0.6 zeptomoles (that’s alyze compound libraries generated as part press together and then separate. The slid10−21 mol) of cocaine from a 10 pg/mL samof chemical evolution and origins-of-life ing version generates charge pulses with al- ple. A standard nanoelectrospray didn’t research at Georgia Tech. He also hopes ternating polarity, depending on the direcproduce any detectable fragment ions from to revisit some of the work that his group tion of motion. The pulses in both versions such a dilute sample. Fernández thinks the has done previously to detect counterfeit contain controlled amounts of charge. improved sensitivity results from a larger pharmaceuticals.—CELIA ARNAUD
CREDIT: ROB FELT/GEORGIA TECH
“It’s probably the cheapest ion source you can think of. You can literally build these for less than $2.00.”
MARCH 6, 2017 | CEN.ACS.ORG | C&EN
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