Research ArticleNANOROBOTS

Mobile nanotweezers for active colloidal manipulation

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Science Robotics  10 Jan 2018:
Vol. 3, Issue 14, eaaq0076
DOI: 10.1126/scirobotics.aaq0076
  • Fig. 1 Mobile nanotweezer.

    (A) Integration of plasmonic nanoparticles with magnetically actuated helical microrobots. The magnetized helical nanostructure can be propelled with small (approximately a few tens of gauss) rotating magnetic fields, whereas the Ag islands upon optical illumination generate strongly localized electric fields that can be used to trap small particles. The shape is crucial to couple magnetically induced rotation of the helix with translation. (B) Schematics of MNT-D1 and MNT-D2. Both designs contained iron as the magnetic element integrated with the helical structure. Whereas D1 contained small plasmonic (silver) nanoparticles distributed across its surface, alternating layers of silver (plasmonic) and iron (magnetic) were incorporated within the structure of D2. (C) Demonstration of trapping, transporting, and releasing colloidal beads with diameters of 1 and 2 μm over 22 μm (from movie S1). The illumination intensity was 18 kW/cm2, and the beads were transported at 1.8 μm/s. (D) Manipulating a collection of 500-nm silica beads at an intensity of 30 kW/cm2 to trace out the letter “N.” Initially, the entire aggregate of particles was trapped, transported, and released. The collection was trapped again and maneuvered in a different path. The beads were released on the way as the optical intensity was reduced en route. Last, the MNT was driven out of the field of view.

  • Fig. 2 Trapping mechanism and differences between the designs.

    (A) Schematic of the different forces acting on MNT-D1 and MNT-D2 showing length scales at which the forces dominate. The electromagnetic near field generates trapping forces (Fem) very close (<100 nm) to both MNT designs, whereas the thermophoretic (Fth) and convective (Fc) forces are only present with design D1. The magnitude of Fth depends on the spatial gradient of temperature and is appreciable within a few micrometers from the MNT-D1, whereas the convective flow can exist up to 100 μm away. (B) Calculated temperature and (C) convective flow velocity as function of distance from the MNT. (D) Minimum illumination intensity to trap as a function of bead size and material (PS and silica) for the two designs. (E) Maximum angular frequency of the MNT-bead system as a function of bead size for a fixed intensity (22 kW/cm2). Error bars represent SD.

  • Fig. 3 Size-selective transport by varying optical intensity and speed.

    (A) Two ways to transport beads selected by size. By reducing the power, the smaller bead can be released, whereas increasing the frequency would release the larger bead. (B) Selectively transporting a 2-μm silica bead (1 μm released) using an optical intensity of 12 kW/cm2. (C) Selectively transporting a 500-nm PS bead and releasing a 1-μm bead by maneuvering the MNT at 1 Hz.

  • Fig. 4 Releasable and permanent trapping.

    (A) Biological materials—here, bacteria (S. aureus)—could be trapped and transported under an illumination of 30 kW/cm2 and subsequently released upon removal of the illumination, as with the silica and PS beads. (B) Fluorescent nanodiamonds were permanently attached to the MNT under an optical illumination of 50 kW/cm2 and subsequently manipulated.

  • Fig. 5 Schemes of nanoscale assembly.

    Scheme 1: MNTs for accurate and fast loading of cargo into existing traps. (A) Time required by MNT in bringing cargo to a trap (dashed line) compared with passive diffusion (solid lines for different cargo sizes) from varying distances. We assume that the MNT-cargo complex is moving at 2 μm/s. (B and C) MNT loading a conventional optical trap (B) and a plasmonic trap (C). Scheme 2: (D) Schematic of optomechanically controlled positioning of the MNT. (E) Static and dynamic nanotweezing, with pinning-unpinning of the MNT on the chamber surface controlled by radiation pressure and magnetic fields. (F) Histogram of fluctuations for an untrapped bead (without laser illumination), along with beads trapped on MNT suspended in a fluid and on MNT pinned to a substrate.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/3/14/eaaq0076/DC1

    Fig. S1. Schematic of the experimental setup.

    Fig. S2. Radial profile of the illumination intensity.

    Fig. S3. Optical transmission data for MNT-D1 peaking around the laser wavelength of 447 nm.

    Fig. S4. Interparticle spacing and size distribution for MNT-D1.

    Fig. S5. Role of thermal effects.

    Fig. S6. Histogram of position fluctuations for an untrapped bead.

    Fig. S7. Minimum intensity required for trapping 1-μm beads versus time.

    Fig. S8. Trap and release of nonfunctionalized nanodiamond.

    Fig. S9. Geometry used in our numerical model.

    Fig. S10. Electric field intensity enhancement.

    Fig. S11. Geometry for simulation.

    Fig. S12. Convective velocity pattern and increased temperature distribution around MNT-D2.

    Fig. S13. Convective velocity pattern and increased temperature distribution around MNT-D1.

    Fig. S14. Experimental estimation of trapping force.

    Fig. S15. Theoretical estimation of trapping force.

    Movie S1. Demonstration of trapping and transport of silica beads of diameter 1 and 2 µm over a distance of 22 µm using MNT-D1.

    Movie S2. Demonstration of trapping and releasing of silica beads of diameter 150 nm using MNT-D1.

    Movie S3. Demonstrating superior spatio-temporal control over particle manipulation by tracing out the letter “N” with MNT-D1.

    Movie S4. Size selective transport of 2 µm Silica beads using MNT-D1.

    Movie S5. Size selective transport of 500 nm PS beads using MNT-D2.

    Movie S6. Demonstration of trapping and releasing of sub-micron size bacteria (Staphylococcus aureus) using MNT-D2.

    Movie S7. Demonstration of trapping and 3D-transport of 120 nm fluorescent nanodiamonds using MNT-D2.

    Movie S8. Demonstration of pinning-depinning mechanism with MNT-D1.

    References (4856)

  • Supplementary Materials

    Supplementary Material for:

    Mobile nanotweezers for active colloidal manipulation

    Souvik Ghosh and Ambarish Ghosh*

    *Corresponding author. Email: ambarish{at}iisc.ac.in

    Published 10 January 2018, Sci. Robot. 3, eaaq0076 (2018)
    DOI: 10.1126/scirobotics.aaq0076

    This PDF file includes:

    • Fig. S1. Schematic of the experimental setup.
    • Fig. S2. Radial profile of the illumination intensity.
    • Fig. S3. Optical transmission data for MNT-D1 peaking around the laser wavelength of 447 nm.
    • Fig. S4. Interparticle spacing and size distribution for MNT-D1.
    • Fig. S5. Role of thermal effects.
    • Fig. S6. Histogram of position fluctuations for an untrapped bead.
    • Fig. S7. Minimum intensity required for trapping 1-μm beads versus time.
    • Fig. S8. Trap and release of nonfunctionalized nanodiamond.
    • Fig. S9. Geometry used in our numerical model.
    • Fig. S10. Electric field intensity enhancement.
    • Fig. S11. Geometry for simulation.
    • Fig. S12. Convective velocity pattern and increased temperature distribution around MNT-D2.
    • Fig. S13. Convective velocity pattern and increased temperature distribution around MNT-D1.
    • Fig. S14. Experimental estimation of trapping force.
    • Fig. S15. Theoretical estimation of trapping force.
    • References (4856)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Demonstration of trapping and transport of silica beads of diameter 1 and 2 μm over a distance of 22 μm using MNT-D1.
    • Movie S2 (.mp4 format). Demonstration of trapping and releasing of silica beads of diameter 150 nm using MNT-D1.
    • Movie S3 (.mp4 format). Demonstrating superior spatio-temporal control over particle manipulation by tracing out the letter "N" with MNT-D1.
    • Movie S4 (.avi format). Size selective transport of 2 μm Silica beads using MNT-D1.
    • Movie S5 (.avi format). Size selective transport of 500 nm PS beads using MNT-D2.
    • Movie S6 (.mp4 format). Demonstration of trapping and releasing of sub-micron size bacteria (Staphylococcus aureus) using MNT-D2.
    • Movie S7 (.mp4 format). Demonstration of trapping and 3D-transport of 120 nm fluorescent nanodiamonds using MNT-D2.
    • Movie S8 (.mp4 format). Demonstration of pinning-depinning mechanism with MNT-D1.

    Files in this Data Supplement:

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