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Shape-based separation of synthetic microparticles

Abstract

The functional properties of colloidal materials can be tailored by tuning the shape of their constituent particles. Unfortunately, a reliable, general methodology for purifying colloidal materials solely based on shape is still lacking. Here we exploit the single-particle analysis and sorting capabilities of the fluorescence-activated cell sorting (FACS) instrument, a commonly used tool in biomedical research, and demonstrate the ability to separate mixtures of synthetic microparticles based solely on their shape with high purity. We achieve this by simultaneously obtaining four independent optical scattering signals from the FACS instrument to create shape-specific ‘scattering signatures’ that can be used for particle classification and sorting. We demonstrate that these four-dimensional signatures can overcome the confounding effects of particle orientation on shape-based characterization. Using this strategy, robust discrimination of particles differing only slightly in shape and an efficient selection of desired shapes from mixtures comprising particles of diverse sizes and materials is demonstrated.

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Fig. 1: Sorting particles by shape using FACS.
Fig. 2: Shape-based sorting of mixtures of microparticles with FACS.
Fig. 3: Optical modelling and simulations of size-, shape- and orientation-dependent scattering.
Fig. 4: High-purity sorting with 4D gates.
Fig. 5: 4D gating enables efficient sorting of diverse mixtures of shapes.

Data availability

Flow cytometry data are available as FCS files in FlowRepository with accession code FR-FCM-ZYR6. All the other data that support the findings of this study are available within the article and its supplementary information files or available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank D. Wu, C. Gordon, C. Wang, P. Coffey and M. Radeke for helpful discussion and technical flow cytometry support. This work was financially supported by DARPA (N66001-14-2-4055). H.T.S. is a Chan Zuckerberg Biohub investigator. The content of the information does not necessarily reflect the position or the policy of the government, and no official endorsement should be inferred.

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Contributions

P.L.M., D.K., C.H. and H.T.S. conceived the project. P.L.M., A.T.C. and D.K. designed the experiments. T.B. synthesized the microparticles and performed scanning electron microscopy. P.L.M. and A.T.C. performed the FACS. P.L.M. analysed the data, designed the sort gates, wrote the analysis and simulation code, performed scattering simulations and performed optical microscopy and image analysis. P.L.M., H.T.S. and M.E. co-wrote and edited the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Samir Mitragotri or Craig Hawker or H. Tom Soh.

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Supplementary information

Supplementary Information

Supplementary Discussion 1–2, Supplementary Figures 1–12, Supplementary Tables 1–2, Supplementary References 1–4

Supplementary Software 1

MATLAB code for simulating the forward scattering (FSC) and side scattering (SSC) intensities of spheres using Mie theory

Supplementary Software 2

Python code for simulating the forward scattering (FSC) and side scattering (SSC) intensities of ellipsoids using the T-matrix method

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Mage, P.L., Csordas, A.T., Brown, T. et al. Shape-based separation of synthetic microparticles. Nature Mater 18, 82–89 (2019). https://doi.org/10.1038/s41563-018-0244-9

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