Mass spectrometers, which are devices that identify chemical substances, are widely used in applications such as crime scene analysis, toxicology testing, and geological surveys. However, these machines are bulky, expensive, and easily damaged, limiting where they can be effectively deployed.
MIT researchers used additive manufacturing to manufacture a mass filter, a core component of a mass spectrometer. This filter is much lighter and cheaper than similar filters made with traditional technology and materials.
Small filters, known as quadrupoles, can be completely manufactured in a few hours for a few dollars. The 3D-printed device is as accurate as some commercial-grade mass filters, which can cost more than $100,000 and take weeks to manufacture.
This filter is made from durable, heat-resistant glass-ceramic resin and is 3D printed in one step, so no assembly is required. During assembly, defects often occur that hinder the performance of the quadrupole.
This lightweight, inexpensive, yet highly accurate quadrupole is one of the key steps in Luis Fernando Velazquez García's 20-year quest to create a 3D-printed portable mass spectrometer.
“We're not the first to try this, but we're the first to do it successfully. There are other small quadrupole filters, but they don't match professional mass filters. “If you can reduce the size and cost without negatively impacting performance, this hardware has a lot of potential,” said MIT Microsystems Technology Laboratory (MTL) principal investigator and director of miniaturized devices. said Velasquez García, lead author of the detailed paper. quadrupole.
For example, scientists can take portable mass spectrometers to remote areas of the rainforest to quickly analyze potential contaminants without having to send samples back to the lab. And lightweight devices could be cheaper and easier to send into space, where they could monitor chemicals in Earth's atmosphere and on distant planets.
Velasquez-Garcia is joined on the paper by first author Colin Ekoff, a graduate student in MIT's Department of Electrical Engineering and Computer Science (EECS). Nicholas Lubinsky, former MIT postdoctoral fellow. and Luke Metzler and Randall Pedder of Ardara Technologies. This research cutting edge science.
size matters
At the heart of a mass spectrometer is a mass filter. This component uses electric or magnetic fields to classify charged particles based on their mass-to-charge ratio. In this way, the device can measure chemical components in a sample and identify unknown substances.
A common type of mass filter, a quadrupole, consists of four metal rods surrounding an axis. A voltage is applied to the rod, creating an electromagnetic field. Depending on the properties of the electromagnetic field, ions with a certain mass-to-charge ratio swirl through the center of the filter, while other particles escape from the sides. By varying the voltage combination, ions with different mass-to-charge ratios can be targeted.
Although the design is very simple, a typical stainless steel quadrupole can weigh several kilograms. However, miniaturizing a quadrupole is not an easy task. Making filters smaller usually introduces errors during the manufacturing process. In addition, smaller filters collect fewer ions, making chemical analysis less sensitive.
“You can't make a quadrupole arbitrarily small; there are tradeoffs,” adds Velasquez-Garcia.
His team balanced this tradeoff by leveraging additive manufacturing to create miniature quadrupoles of ideal size and shape to maximize accuracy and sensitivity.
They make their filters from glass-ceramic resin, a relatively new printable material that can withstand temperatures up to 900 degrees Celsius and performs well in vacuum.
This device is fabricated using a vat photopolymerization method. In this process, the piston is forced into a vat of liquid resin until it nearly touches the LED array at the bottom. This emits light and hardens the resin left in the tiny gap between the piston and the LED. A small layer of hardened polymer is applied to a piston, which then rises and repeats the cycle, building the device one small layer at a time.
“This is a relatively new technology for printing ceramics that allows you to create very precise 3D objects. And one of the key benefits of additive manufacturing is that you can actively iterate on your designs,” says Velasquez.・Mr. Garcia says.
Because 3D printers can form virtually any shape, the researchers designed a quadrupole with hyperbolic rods. This shape is ideal for mass filtering, but difficult to create using traditional methods. Many commercially available filters use round rods instead, which can reduce performance.
It is also printed with an intricate network of triangular lattices surrounding the rod, which provides durability and ensures that the rod remains in the correct position even if the device moves or shakes.
To complete the quadrupole, the researchers used a technique called electroless plating to coat the rods with a thin metal film, making them electrically conductive. All but the rods are covered with masking chemicals and the quadrupole is immersed in a chemical bath heated to precise temperature and agitation conditions. This uniformly deposits a thin metal film on the rod without damaging the rest of the device or shorting the rod.
“In the end, we were able to create the most compact yet most accurate quadrupole given the limitations of the 3D printer,” says Velasquez García.
Maximize performance
To test the 3D-printed quadrupole, the team replaced them with a commercial system and found that they could achieve higher resolution than other types of small filters. At approximately 12 centimeters long, the quadrupole is one-fourth as dense as a comparable stainless steel filter.
Additionally, further experiments suggest that the 3D printed quadrupole can achieve accuracy comparable to large-scale commercial filters.
“Mass spectrometry is one of the most important of all scientific tools, and Velázquez-García and colleagues have designed a quadrupole mass filter, which has several advantages over previous instruments, construction, and performance,” said Dr. Graham Cooks of Henry. Vaughn Hass, Distinguished Professor of Chemistry at Purdue University's Aston Mass Spectrometry Laboratory, was not involved in the study. “The advantage stems from these facts: it is much smaller and lighter than most commercially available products, and is manufactured monolithically using a layered structure.” …while relying on the same electric field for mass measurements , it is an open question how comparable the performance is with quadrupole ion traps, which do not have strict geometrical requirements such as quadrupole mass filters. ”
“This paper represents a real advance in the fabrication of quadrupole mass filters (QMFs). The authors combine their knowledge of advanced materials, QMF drive electronics, and fabrication using mass spectrometry to… We have created a new system with superior performance at a lower cost,” added Steve Taylor, Professor of Electrical and Electronic Engineering at the University of Liverpool. This is also not related to this article. “This paper has important implications across the field of mass spectrometry, which represents a multi-billion dollar industry worldwide, as QMF is at the heart of the 'analytical engine' in many other types of mass spectrometry systems. Masu.”
In the future, the researchers plan to improve the quadrupole's performance by making the filters longer. Longer filters allow for more accurate measurements because as the chemicals move along their length, more ions that would otherwise be filtered escape. They also plan to explore different ceramic materials that can better transfer heat.
“Our vision is to create a mass spectrometer in which all major components can be 3D printed, contributing to devices with significantly reduced weight and cost without sacrificing performance. There is still much work to be done. Yes, but this is a great start,” Velasquez-Garcia added.
This research was funded by Empiriko Corporation.
