Mass Spectrometry Performance Improved by Triboelectric Nanogenerators

Mechanical energy harvested from the environment is converted into electricity by triboelectric nanogenerators (TENG). This electricity is used to recharge consumer electronics or powering small devices such as sensors.

Researchers have now harnessed these devices to enhance the charging of molecules in a manner that dramatically improves the sensitivity of a widely-employed chemical analysis technique.

Researchers at the Georgia Institute of Technology have demonstrated that replacing standard power supplies with TENG devices for charging the molecules being examined can improve the sensitivity of mass spectrometers to exceptional levels. With this improvement it is also possible to carry out the identification process with smaller sample volumes, potentially conserving chemical mixtures or precious biomolecules that could be available only in very small quantities.

Even though the mechanism by which the improvement takes place needs additional study, the researchers assume that the unique aspects of the TENG output, oscillating controlled current and high voltage, permit enhancements in the ionization process, thus bringing about an increase in the voltage applied without damaging the instrument or samples.

The research, published in the February 27 issue of the journal Nature Nanotechnology, was supported by the National Science Foundation, NASA Astrobiology Program and the Department of Energy.

Our discovery is basically a new and very controlled way of putting charge onto molecules. We know exactly how much charge we produce using these nanogenerators, allowing us to reach sensitivity levels that are unheard-of – at the zeptomole scale. We can measure down to literally hundreds of molecules without tagging.

Facundo Fernández, Professor in Georgia Tech

Fernández  uses mass spectrometry to analyze everything from tiny drug molecules to large protein.

Fernández and his team of researchers worked with Zhong Lin Wang, a pioneer in developing the TENG technology. Wang, a Regents professor in Georgia Tech’s School of Materials Science and Engineering, stated that the TENGs provide reliable charging levels that develop quantized ion pulses of adjustable duration, frequency and polarity.

The key here is that the total charge delivered in each cycle is entirely controlled and constant regardless of the speed at which the TENG is triggered. This is a new direction for the triboelectric nanogenerators and opens a door for using the technology in the design of future instrumentation and equipment. This research demonstrates another practical impact of TENG technology.

Zhong Lin Wang, Professor, Georgia Tech

Wang holds the Hightower Chair in the School of Materials Science and Engineering.

The mass-to-charge ratio of ions is measured by mass spectrometry in order to identify and quantify molecules in both complex and simple mixtures. The technology is employed in a wide range of scientific applications and scientific fields, with molecules ranging from tiny small drug compounds up to large biomolecules.

Mass spectrometry is employed in drug discovery, systems biology, homeland security, food science, biomedicine and other areas.

However, in standard electrospray mass spec techniques, almost 99% of the sample can be wasted during the process of ionization, stated Fernández, who holds the Vasser Woolley Foundation Chair in Bioanalytical Chemistry.

This is mainly due to the fact that in standard systems, the mass analysis process is scanned or pulsed, while the ionization of samples is nonstop. The new TENG pulsed power source allows scientists to set a time to the ionization in order to match what happens inside the mass spectrometer, particularly within a component called the mass analyzer.

The new technique allows ion deposition on surfaces, even non-conducting ones, in addition to allowing enhanced ability and sensitivity to analyze extremely small sample quantities. This is because the oscillating ionization develops a sequence of alternating negative and positive charges, creating a net neutral surface, Fernández stated.

Increased amounts of power are required by mass spectrometers to develop the vacuum that is important for measuring the mass-to-charge ratio of all molecules. Currently, the TENG devices are used to only ionize samples despite the possibility of future TENG devices to power an entire miniature mass spectrometer.

The nanogenerators could eliminate a big chunk of the mass spectrometer system because they wouldn’t need a more powerful device for making the ions. This could be particularly applicable to conditions that are extreme and harsh, such as on a battlefield or in space, where you would need a very robust and self-contained unit.

Facundo Fernández, Professor in Georgia Tech

Developed by Wang in 2012, triboelectric nanogenerators use a blend of the electrostatic induction and triboelectric effect in order to produce minimal amounts of electrical power from mechanical motion such as vibration, sliding or rotation. The triboelectric effect takes advantage of the fact that specific materials become electrically charged only after they enter the moving contact with a surface developed from a different material.

TENGs with four different working modes were developed by Wang and his team of researchers. A rotating disc that could be perfect for high throughput mass spectrometry experiments was also developed by the team. This paper is considered to be the first publication about an application of TENG to an enhanced instrument.

Voltage levels at the mass spec ionizer of between 6,000 and 8,000 volts were measured by Wang’s researchers. Normally, conventional ionizers operate at less than 1,500 volts. The technology has been used with both plasma discharge ionization and electrospray ionization, together with the flexibility of producing alternating polarity or single polarity ion pulses.

Because the voltage from these nanogenerators is high, we believe that the size of the sample droplets can be much smaller than with the conventional way of making ions. That increases the ion generation efficiency. We are operating in a completely different electrospray regime, and it could completely change the way this technology is used.

Facundo Fernández, Professor in Georgia Tech

It is possible to retrofit the TENG technology to the already available mass spectrometers, as Fernández has previously done in his lab. Fernández, with publication of the journal article, hopes that other labs will begin to explore the use of the TENG devices in mass spectrometry and various other areas. “I see potential not only in analytical chemistry, but also in synthesis, electrochemistry and other areas that require a controlled way of producing electrical charges,” Fernández said.

The research was carried out by postdoctoral fellows in the two laboratory groups, Anyin Li and Yunlong Zi. “This project really shows how innovation can happen at the boundaries between different disciplines when scientists are free to pursue new ideas,” Fernández added.

Both NSF and the NASA Astrobiology Program supported this work, under the NSF Center for Chemical Evolution, CHE-1504217. Research was also supported by the U.S. Department of Energy, Office of Energy Sciences (Award DE-FG02-07ER46394), and the National Science Foundation (DMR-1505319).

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