Researchers 3D print key components for point-of-care mass spectrometer. MIT News

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Mass spectrometry, a technique that can accurately identify the chemical components of a sample, can be used to monitor the health of people suffering from chronic diseases. For example, a mass spectrometer can measure hormone levels in the blood of someone with hypothyroidism.

But mass spectrometers can cost several hundred thousand dollars, so these expensive machines are generally limited to laboratories where blood samples must be sent for testing. This ineffective process can make management of a chronic disease particularly challenging.

“Our big goal is to localize mass spectrometry. Someone who has a chronic disease that requires constant monitoring may have something the size of a shoebox that they can use to perform this test at home. For this to happen, the hardware needs to be cheap,” says Luis Fernando Velasquez-Garcia, principal research scientist at MIT’s Microsystems Technology Laboratories (MTL).

He and his colleagues have taken a major step in that direction by 3D printing a low-cost ionizer – a critical component of all mass spectrometers – that performs twice as well as its state-of-the-art counterparts.

Their instrument, which is only a few centimeters in size, can be manufactured in large-scale batches and then incorporated into a mass spectrometer using efficient, pick-and-place robotic assembly methods. Such mass production would make it cheaper than typical ionizers, which often require manual labor, require expensive hardware to interface with mass spectrometers, or must be built in semiautomatic clean rooms. .

By 3D printing the device instead, the researchers were able to precisely control its shape and use special materials, which helped boost its performance.

“This is a do-it-yourself approach to building an ionizer, but it is not a device put together with duct tape or a poor man’s version of the device. At the end of the day, it works better than devices made using expensive processes and specialized equipment, and anyone can be empowered to make it,” says Velasquez-Garcia, senior author of the study. paper on ionizer,

He wrote the paper with lead author Alex Kachkin, a mechanical engineering graduate student. Research has been published Journal of the American Association for Mass Spectrometry,

low cost hardware

Mass spectrometers identify the contents of a sample by sorting charged particles, called ions, based on their mass-to-charge ratio. Since the molecules in blood do not have an electrical charge, an ionizer is used to charge them before they are analyzed.

Most liquid ionizers do this using electrospray, which involves applying high voltage to a liquid sample and then firing a thin jet of charged particles into the mass spectrometer. The more ionized particles in the spray, the more accurate the measurement will be.

MIT researchers used 3D printing with some clever optimizations to produce a low-cost electrospray emitter that outperformed state-of-the-art mass spectrometry ionizer versions.

They fabricated the emitter from metal using binder jetting, a 3D printing process in which a blanket of powdered material is sprayed through tiny nozzles with a polymer-based glue to build up an object layer by layer . The finished object is heated in an oven to evaporate the glue and then consolidated with a bed of powder surrounding the object.

“The process sounds complicated, but it is one of the basic 3D printing methods, and it is highly accurate and very effective,” says Velasquez-Garcia.

Then, the printed emitters go through an electropolishing step which sharpens it. Finally, each device is coated in zinc oxide nanowires that give the emitter a level of porosity that enables it to effectively filter and transport liquids.

Thinking outside the box

One potential problem that affects electrospray emitters is evaporation that can occur in the liquid sample during operation. The solvent can vaporize and clog the emitter, so engineers typically design emitters to limit evaporation.

Through modeling confirmed by experiments, the MIT team realized they could use evaporation to their advantage. They designed the emitters as externally fed solid cones with a specific angle that takes advantage of evaporation to strategically restrict the flow of liquid. Thus, the sample spray has a higher proportion of charge carrying molecules.

“We saw that evaporation can actually be a design knob that can help you optimize performance,” he says.

They also reconsidered the counter-electrode that applies voltage to the sample. The team optimized its size and shape using a similar binder jetting method to prevent electrode bulging. Arcing, which occurs when electrical current crosses the gap between two electrodes, can damage the electrodes or cause overheating.

Because their electrodes are not prone to arcing, they can safely increase the applied voltage, resulting in more ionized molecules and better performance.

They also created a low-cost printed circuit board with built-in digital microfluidics, in which the emitter is soldered. The addition of digital microfluidics enables the ionizer to transport liquid droplets efficiently.

Overall, these optimizations enabled an electrospray emitter that can operate at 24 percent higher voltage than state-of-the-art versions. This higher voltage enabled his device to more than double the signal-to-noise ratio.

Furthermore, their batch processing technology can be implemented on a large scale, which will significantly reduce the cost of each emitter and go a long way toward making point-of-care mass spectrometers an affordable reality.

“Going back to Gutenberg, once people had the ability to print their own things, the world completely changed. In a sense, it may be something more than that. “We can give people the power to create the hardware they need in their daily lives,” he says.

Moving forward, the team wants to create a prototype that combines their ionizer with a 3D-printed mass filter they previously developed. Ionizer and mass filter are the major components of the device. They are also working to improve 3D-printed vacuum pumps, which remain a major hurdle in printing an entire compact mass spectrometer.

“Miniaturization through advanced technology is slowly but surely transforming mass spectrometry, reducing manufacturing costs and increasing the range of applications. This work on the fabrication of electrospray sources by 3D printing also increases signal strength, increases sensitivity and signal-to-noise ratio and potentially opens the way to more widespread use in clinical diagnostics,” Electrical says Richard Sims, professor of microsystems technology in the department. and Electronic Engineering at Imperial College London, who were not involved in this research.

This work was supported by Empirico Corporation.

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