Optical fibres inspire novel approach to nano-electrospray

Electrospray ionization is a mass spectrometry technique for analysing large molecules such as proteins or peptides, which are key to disease detection and drug development. However, the tapered shape of the tiny, needle-like nozzles, or electrospray emitters, used to “spray” samples into the mass spectrometer for analysis were prone to clogging, necessitating constant monitoring of the process and frequent replacement of the costly emitter tips, which affected the reproducibility of results.

For the past several years the professor of chemistry and his research team at Queen’s University have been developing innovations to improve the performance of these minuscule nozzles. Dr. Oleschuk and his group developed a silica-based, non-tapered emitter with multiple channels that resolved the clogging problem while enhancing the emitter’s reliability and performance. This innovation was patented in 2013.

However, working with silica is expensive, and Dr. Oleschuk began casting around for other material alternatives, such as polymers, that could replicate the sensitivity and performance of traditional emitters. A chance image on a colleague’s computer screen of a multi-structured fibre used by the photonics industry provided a possible answer.

If this slender fibre tube, composed of multiple “channels”, each approximately the diameter of a red blood cell, could be used to transmit light, he reasoned, why not use it to transmit fluids? The idea was sound, but the design of the optical fibre had some limitations.

“We hoped that each one of these narrow tubes would act as its own emitter, but when we tried to spray the liquid, the holes were so closely spaced together, the liquid coalesced,” Oleschuk explains. The solution was to make a more electrospray-compatible design, but fabricating such a material was expensive.

That barrier was overcome with $20K in proof of principle funding and engineering expertise from CMC Microsystems, and a partnership with an Australian materials manufacturer, enabling the researchers to design, prototype and test five types of customized polymer fibres with different hole arrangements. Dr. Oleschuk believes it was the first time anyone had explored the use of these novel materials for nanoelectrospray applications. “We showed that you could get multiple sprays from a single tube—up to that point no one had done that,” he says.

That combination of funding and prototyping assistance helped the project attract industrial partners in the mass spectrometry business, and it stimulated follow-on funding from other organizations, including a $350,000 NSERC grant in 2011 for further investigation of the microstructured fibres.

However, there were other challenges. The polycarbonate material wasn’t resistant to analyte solvents, and the use of non-water-based solvents on the hydrophobic surface of the emitter caused the sprays to coalesce. “That led to the realization that the fibre needed nozzles to protrude off the surface, and to constrain the liquid to spray from the tubes—like you see in a shower head,” Oleschuk explains.

Creating the protruding tubes required many steps, including multiple chemical reactions and complex chemical etching processes, so the group began looking at other material alternatives. A subsequent collaboration with Professor Younès Messaddeq, a Canada Excellence Research Chair in Photonics at Université Laval, resulted in a new type of fibre with the characteristics the group needed.

“He created something absolutely beautiful, and we developed a way to modify it and use it in our applications,” Oleschuk says. “It’s a different fibre, with protruding nozzles of silica, so it’s stronger and more resistant to solvents.”

The technology has attracted the interest of a Canadian industrial partner, and the underlying research knowledge is being shared with other Canadian researchers by CMC through its knowledge repository.

The emitter also has potential for lab-on-a-chip applications in related research by the Oleschuk lab into droplet-based microfluidic platforms. This work was enabled through their collaboration with CMC Microsystems on the development of a microsystems integration platform (MiP) for microfluidics. Thanks to his lab’s work, this technology evaluation and development tool is now being made available by CMC to researchers across the National Design Network.

Oleschuk and his team are now working with CMC to explore the development of a nanoparticle-based coating technology for enhanced droplet-based microfluidic platforms—work that will be completed in Queen’s newly opened Nano-Fabrication Laboratory. When completed, the functionalized nanoparticles will be made available to innovators across the National Design Network.