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Upconversion particle-based optical tweezers for sensing applications

Nature Protocols (2026)Cite this article

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Abstract

Optical tweezers use focused laser beams to manipulate small particles, primarily for force sensing. Recent advances in nanoscale-trapping approaches have enabled the development of multiplexed sensing applications, such as temperature and viscosity detection. Upconversion particles (UCPs) and, in particular, lanthanide-doped nano-/micro-crystals (~6 nm to 6 μm) exhibit particular anti-Stokes emission properties, which facilitate their visualization when trapped and the detection of changes to their properties based on temperature and orientation. Their ion resonance enhances the trapping force, enabling the manipulation of smaller particles and their use for force sensing. Here we provide step-by-step instructions to build UCP-based holographic optical tweezers systems, including super-resolved photonic force microscopy and fluorescence optical tweezers. We detail the characterization of the setup for subfemtonewton-scale force sensing and include nanoprobe functionalization, force sensitivity validation and comparison with known forces. We further include the procedures for temperature and viscosity sensing, such as calibrating polarized spectra, initiating UCP rotation and analyzing viscosity via spectral fluctuations. Applications, including nanoparticle-DNA-coated gold film interactions and temperature distribution near single cells, are shown as well. The procedure typically requires 6 days to complete and is suitable for users with expertise in photonics.

Key points

  • The procedure describes the use of lanthanide ion-doped upconversion particles, trapped and excited using a 980 nm laser and detected using a high-speed scientific complementary metal–oxide–semiconductor camera, a spectrometer, an optical astigmatism component and a machine-learning-aided three-dimensional localization algorithm to construct the super-resolved fluorescence optical tweezers.

  • The Protocol enables subfemtonewton-level force sensing, intracellular viscosity measurements and local temperature sensing, supporting research including subcellular environment measuring and biomolecular long-distance interaction.

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Fig. 1: The schematic of the single-gradient optical tweezers system.
Fig. 2: The schematic and actual experimental setup photograph of the super-resolved photonic force microscope.
Fig. 3: LUT measurement system characterization.
Fig. 4: An example of ring mask for finding the pupil size of objective lens.
Fig. 5: The schematic of the optical system for coupling a spectrometer to the optical tweezer system.
Fig. 6: Optical trapping of a single upconverting nanoparticle.
Fig. 7: Rotated upconverting microparticle and its corresponding spectral changes.
Fig. 8: Upconverting nanoparticle under Brownian angular fluctuation and its spectral changes.
Fig. 9: Spectral response at different temperatures.
Fig. 10: Validation of force sensitivity at the nanoscale.
Fig. 11: Force sensing on a single UCNP.
Fig. 12: Interaction force sensing between UCNP and DNA-functionalized Au surface.
Fig. 13: Results of viscosity sensing obtained from rotated UCMPs and angularly fluctuating UCNPs.
Fig. 14: Results of extracellular thermal scanning enabled by a single upconverting microparticle.

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Data availability

The data that support the findings of this study are available within the article and its Supplementary Information. Other relevant data are available from the corresponding authors upon reasonable request.

Code availability

All the custom codes are available from the corresponding authors upon reasonable request.

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Acknowledgements

This work was supported by the National Natural Science Foundation of China (grant nos. 62275010, 62405015 and U23A20481), the Beijing Natural Science Foundation (grant no. 1232027). This work was also financed by grant nos. PID2023-146775OB-I00 and PID2023-151078OB-I00, grant no. CNS2022-135495 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR, by the Comunidad Autónoma de Madrid (grant no. S2022/BMD-7403 RENIM-CM) and cofinanced by the European structural and investment fund. F.Z. acknowledges the scholarship from the China Scholarship Council (grant no. 202108440235). F.Z., P.H.-G. and D.J. thank P. Rodríguez Sevilla and E. Ortiz Rivero for their past contributions to Nanomaterials Bioimaging Group. T.Z., X.S. and F.W. thank L. Ding and D. Wang for their contributions to Fan Lab. We acknowledge equipment support from the Analysis and Testing Center in Beihang University, Beijing.

Author information

Author notes

  1. These authors contributed equally: Tiange Zhang, Fengchan Zhang.

Authors and Affiliations

  1. School of Physics, Beihang University, Beijing, People’s Republic of China

    Tiange Zhang, Xuchen Shan & Fan Wang

  2. Nanomaterials for Bioimaging Group, Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid, Spain

    Fengchan Zhang, Patricia Haro-González & Daniel Jaque

  3. Instituto Nicolás Cabrera, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid, Spain

    Fengchan Zhang, Patricia Haro-González & Daniel Jaque

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  1. Tiange Zhang
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Contributions

F.W., D.J., P.H. and X.S. designed and implemented the fabrication protocol. F.W., D.J. and X.S designed the optical setup for optical tweezers. T.Z. contributed to the experimental work shown in this Protocol. T.Z. and F.Z. contributed to the visualization, collection and adaptation of the figures. T.Z., F.Z., X.S., P.H., D.J. and F.W. wrote the Protocol. F.W. and D.J. supervised the study and the manuscript preparation. All authors reviewed and edited the manuscript and approved the final version.

Corresponding authors

Correspondence to Xuchen Shan, Patricia Haro-González, Daniel Jaque or Fan Wang.

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The authors declare no competing interests.

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Nature Protocols thanks Ye Pu and Shi-Wei Chu and the other, anonymous reviewer(s) for their contribution to the peer review of this work.

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Key references

Shan, X. et al. Nat. Nanotechnol. 16, 531–537 (2021): https://doi.org/10.1038/s41565-021-00852-0

Shan, X. et al. Nat. Photon. 18, 913–921 (2024): https://doi.org/10.1038/s41566-024-01462-7

Rodríguez-Sevilla, P. et al. Adv. Biosys. 3, 1900082 (2019): https://onlinelibrary.wiley.com/doi/10.1002/adbi.201900082

Ortiz-Rivero, E. et al. Small Methods 9, 2400718 (2025): https://doi.org/10.1002/smtd.202400718

Supplementary information

Supplementary Information

(1): laser-induced temperature increases in the optical trap. (2): scanning electron microscope images of hexagonal upconverting particles. (3): polarized emission from a single β-NaYF4:Yb3+,Er3+ upconverting particle

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Zhang, T., Zhang, F., Shan, X. et al. Upconversion particle-based optical tweezers for sensing applications. Nat Protoc (2026). https://doi.org/10.1038/s41596-025-01264-3

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