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Geometry-induced electrostatic trapping of nanometric objects in a fluid

Abstract

The ability to trap an object—whether a single atom or a macroscopic entity—affects fields as diverse as quantum optics1, soft condensed-matter physics, biophysics and clinical medicine2. Many sophisticated methodologies have been developed to counter the randomizing effect of Brownian motion in solution3,4,5,6,7,8,9,10, but stable trapping of nanometre-sized objects remains challenging8,9,10. Optical tweezers are widely used traps, but require sufficiently polarizable objects and thus are unable to manipulate small macromolecules. Confinement of single molecules has been achieved using electrokinetic feedback guided by tracking of a fluorescent label, but photophysical constraints limit the trap stiffness and lifetime8. Here we show that a fluidic slit with appropriately tailored topography has a spatially modulated electrostatic potential that can trap and levitate charged objects in solution for up to several hours. We illustrate this principle with gold particles, polymer beads and lipid vesicles with diameters of tens of nanometres, which are all trapped without external intervention and independently of their mass and dielectric function. The stiffness and stability of our electrostatic trap is easily tuned by adjusting the system geometry and the ionic strength of the solution, and it lends itself to integration with other manipulation mechanisms. We anticipate that these features will allow its use for contact-free confinement of single proteins and macromolecules, and the sorting and fractionation of nanometre-sized objects or their assembly into high-density arrays.

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Figure 1: Pictorial overview of the device and experimental set-up.
Figure 2: Transverse and axial confinement of a 100-nm gold particle by pocket nanostructures.
Figure 3: Electrostatic potential in a topographically structured fluidic nanoslit.
Figure 4: Trapping single lipid vesicles.

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Acknowledgements

We thank A. Alt for expert assistance in electron-beam lithography and the staff of the Center for Micro- and Nanoscience (FIRST), ETH Zurich, for clean-room support; H. Ewers for assistance in producing lipid vesicles; M. Celebrano and A. Renn for experimental input; M. Agio for discussions; and E. Petrov and R. Klemm for reading the manuscript. M.K. acknowledges a Marie Curie Intra-European Fellowship for Career Development of the European Commission, and greatly appreciates the support of B. Eichler, I. Mönch and P. Schwille in the early stages of the project.

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Authors

Contributions

M.K. conceived the research, designed the experiments and performed the theoretical analysis. N.M. and M.K. performed the experiments and analysed the data. P.K. and V.S. provided expertise on iSCAT. M.K. and V.S. wrote the manuscript.

Corresponding author

Correspondence to Madhavi Krishnan.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figure 1 with a legend and legends for Supplementary Movies 1-7. (PDF 129 kb)

Supplementary Movie 1

This movie shows guided diffusion of a gold particle along a groove – see Supplementary Information file for full legend. (AVI 716 kb)

Supplementary Movie 2

The movie shows gold particles trapped by pocket nanostructures – see Supplementary Information file for full legend. (AVI 129 kb)

Supplementary Movie 3

This movie shows gold particles trapped by pocket nanostructures – see Supplementary Information file for full legend. (AVI 572 kb)

Supplementary Movie 4

This movie shows Stable trapping of a single gold particle – see Supplementary Information file for full legend. (AVI 704 kb)

Supplementary Movie 5

This movie shows stiff trapping of single gold particles – see Supplementary Information file for full legend. (AVI 129 kb)

Supplementary Movie 6

This movie shows stable trapping of single lipid vesicles – see Supplementary Information file for full legend. (AVI 185 kb)

Supplementary Movie 7

This movie shows trapping single polystyrene particles along arbitrary contours – see Supplementary Information file for full legend. (AVI 288 kb)

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Krishnan, M., Mojarad, N., Kukura, P. et al. Geometry-induced electrostatic trapping of nanometric objects in a fluid. Nature 467, 692–695 (2010). https://doi.org/10.1038/nature09404

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