Researchers 3D print rotating microfilter for lab-on-a-chip applications


PICTURE: The researchers made tiny, magnetically driven rotary filters for use in microfluidic channels. Filters are only 70 microns wide and 60 microns high with square openings that measure 6.5 microns … see After

Credit: Dong Wu, China University of Science and Technology

WASHINGTON – Researchers have manufactured a magnetically driven rotary microfilter that can be used to filter particles inside a microfluidic device. They made the tiny spinning filter by creating a magnetic material that could be used with a very precise 3D printing technique known as two-photon polymerization.

Microfluidic devices, also known as lab-on-a-chip devices, can be used to perform multiple lab functions inside a chip that is typically a few square centimeters or less. These devices contain complex networks of microfluidic channels and become increasingly complex. They can be useful for a variety of applications such as screening molecules for their therapeutic potential or performing blood tests that detect disease.

“By changing the direction of the external magnetic field, the microfilter we made can be remotely manipulated on demand to filter out particles of certain sizes or to allow them all to pass,” said Dong Wu, a team member. research center of the University of Science and Technology of China. “This functionality could be used for many types of chemical and biological studies performed in lab-on-a-chip devices and, most importantly, enables the reuse of the chips.”

In the journal The Optical Society (OSA) Optical letters, Wu and colleagues at Hefei University of Technology and the RIKEN Center for Advanced Photonics in Japan show that their new rotary microfilters can sort particles in a high-performance microfluidic device.

“This filter could potentially be used to sort cells of different sizes for applications such as isolating circulating tumor cells for analysis or detecting abnormally large cells that may indicate disease,” said Chaowei Wang of the University of Montreal. science and technology from China. “With further developments, it might even be possible to use it in devices placed inside the body for cancer detection.”

A more versatile filter

Filters with micrometric holes are often used in microfluidic chips as a passive means of sorting particles or cells based on the size of the holes. However, since the number and shape of the holes in the filter cannot be changed dynamically, the available devices lack the flexibility to sort different types of particles or cells on demand. To extend the utility of microfluidic devices, researchers developed a filter that can freely switch between modes such as selective filtering and pass-through.

They created the new filter using two-photon polymerization, which uses a focused femtosecond laser beam to solidify or polymerize a light-sensitive liquid material known as a photoresist. Thanks to the two-photon absorption, the polymerization can be done very precisely, allowing the fabrication of complex structures at the micron scale.

To make the microfilter, the researchers synthesized magnetic nanoparticles and mixed them with the photosensitive resin. Manufacturing the rotary microfilter required them to optimize the laser power density, number of pulses, and scan intervals used for polymerization. After testing its magnetic properties on a glass slide, they integrated the microfilter into a microfluidic device.

Several filtering modes

To filter out larger particles, a magnetic field perpendicular to the microchannel is applied. Once the filtering process is complete, large particles can be released by applying a magnetic field parallel to the microchannel, which will rotate the microfilter 90 °. The filtering process can then be repeated as needed.

The researchers verified the filtering performance of the filter using polystyrene particles with a diameter of 8.0 and 2.5 microns mixed in an alcohol solution. “It was clear that particles smaller than the pore size easily passed through the microfilter while the larger ones were filtered out,” said Chenchu ​​Zhang of the China University of Science and Technology. “In pass-through mode, any larger particles captured by the filter have been washed away by the fluid, which prevents filter clogging and allows reuse of the microfilter.”

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Article: C. Wang, Z. Hu, L. Yang, C. Zhang, L. Zhang, S. Ji, L. Xu, J. Li, Y. Hu, D. Wu, J. Chu, K. Sugioka, “Magnetically driven rotary microfilter manufactured by two-photon polymerization for multimode filtering of particles”, Opt. Lett., 46, 12, 2968-2971 (2021).

DOI: https: //do I.org /ten.1364 /OL.428751.

About Optical letters

Optical letters offers rapid dissemination of new findings in all areas of optical science with short, original and peer-reviewed papers. Optical letters accepts articles which are remarkable for a substantial part of the optical community. Published by The Optical Society and edited by Editor-in-Chief Miguel Alonso, Institut Fresnel, École Centrale de Marseille and Aix-Marseille University, France, University of Rochester, United States. Optical letters is available online at OSA Publishing.

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