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Microlensed fiber allows subcellular imaging by laser-based mass spectrometry

Nature Protocols volume 18, pages 2558–2578 (2023)Cite this article

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Abstract

Mass spectrometry imaging (MSI) enables the chemical mapping of molecules and elements in a label-free, high-throughput manner. Because this approach can be accomplished rapidly, it also enables chemical changes to be monitored. Here, we describe a protocol for MSI with subcellular spatial resolution. This is achieved by using a microlensed fiber, which is made by grinding an optical fiber. It is a universal and economic technique that can be adapted to most laser-based mass spectrometry methods. In this protocol, the output of laser radiation from the microlensed fiber causes laser ablation of the sample, and the resulting plume is mass spectrometrically analyzed. The microlensed fiber can be used with matrix-assisted laser desorption ionization, laser desorption ionization, laser ablation electrospray desorption ionization and laser ablation inductively coupled plasma, in each case to achieve submicroscale imaging of single cells and biological tissues. This report provides a detailed introduction of the microlensed fiber design and working principles, sample preparation, microlensed fiber ion source setup and multiple MSI platforms with different kinds of mass spectrometers. A researcher with a little background (such as a trained graduate student) is able to complete all the steps for the experimental setup in ~2 h, including fiber test, laser coupling and ion source modification. The imaging time spent mainly depends on the size of the imaging area. It is suggested that most existing laser-based MSI platforms, especially atmospheric pressure applications, can achieve breakthroughs in spatial resolution by introducing a microlensed fiber module.

Key points

  • A microlens capable of focusing laser radiation is formed by rounding one end of an optical fiber. Focusing light on smaller spots improves the resolution of laser desorption or ablation sample surfaces, making nanoscale mass spectrometry imaging analysis possible.

  • Microlensed fibers can be incorporated into matrix-assisted laser desorption ionization, laser desorption ionization, laser ablation electrospray desorption ionization and laser ablation inductively coupled plasma setups.

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Fig. 1: Development of the microlensed fiber and its positioning.
Fig. 2: Schematics of different types of laser-based MSI platforms with the microlensed fiber.
Fig. 3: Spatial resolution of the MSI with a microlensed fiber.
Fig. 4: Tissue imaging achieved by laser-based MSI with a microlensed fiber.
Fig. 5: Single-cell imaging achieved by laser-based MSI with the microlensed fiber.

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Data availability

The data presented in Anticipated results are from previous publications22,24,26 and are available from the corresponding authors. The figures have been rearranged and embedded.

Code availability

The LabVIEW and MATLAB programs are available from https://github.com/yfmeng1121/SmarAct-micropositioner-control.

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Acknowledgements

This work is supported by the Natural Science Foundation of China (21974116 and 22027808) and the Air Force Office of Scientific Research through the Multidisciplinary University Research Initiative (MURI) program (AFOSR FA9550-21-1-0170).

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Authors and Affiliations

  1. Ministry of Education (MOE) Key Laboratory of Spectrochemical Analysis and Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China

    Yifan Meng & Wei Hang

  2. Department of Chemistry, Stanford University, Stanford, CA, USA

    Yifan Meng & Richard N. Zare

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  1. Yifan Meng
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  2. Wei Hang
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Contributions

W.H., R.N.Z. and Y.M. developed the procedure. Y.M. performed the imaging experiments and processed the data. The manuscript was written by all authors.

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Correspondence to Wei Hang or Richard N. Zare.

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Nature Protocols thanks Li Yang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Key references using this protocol

Meng, Y. et al. Angew. Chem. Int. Ed. Engl. 59, 17864–17871 (2020): https://doi.org/10.1002/anie.202002151

Meng, Y. et al. ACS Nano 15, 13220–13229 (2021): https://doi.org/10.1021/acsnano.1c02922

Meng, Y. et al. Anal. Chem. 94, 10278–10282 (2022): https://doi.org/10.1021/acs.analchem.2c01942

Supplementary information

Supplementary Information

Supplementary Figs. 1–12

Reporting Summary

Supplementary Video 1

MS imaging of a marker pen pattern (sample) on a glass slide with a microlensed fiber

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Meng, Y., Hang, W. & Zare, R.N. Microlensed fiber allows subcellular imaging by laser-based mass spectrometry. Nat Protoc 18, 2558–2578 (2023). https://doi.org/10.1038/s41596-023-00848-1

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