Optical manipulation of nanoparticles and biomolecules in sub-wavelength slot waveguides

Abstract

The ability to manipulate nanoscopic matter precisely is critical for the development of active nanosystems. Optical tweezers are excellent tools for transporting particles ranging in size from several micrometres to a few hundred nanometres. Manipulation of dielectric objects with much smaller diameters, however, requires stronger optical confinement and higher intensities than can be provided by these diffraction-limited systems. Here we present an approach to optofluidic transport that overcomes these limitations, using sub-wavelength liquid-core slot waveguides. The technique simultaneously makes use of near-field optical forces to confine matter inside the waveguide and scattering/adsorption forces to transport it. The ability of the slot waveguide to condense the accessible electromagnetic energy to scales as small as 60 nm allows us also to overcome the fundamental diffraction problem. We apply the approach here to the trapping and transport of 75-nm dielectric nanoparticles and lambda-DNA molecules. Because trapping occurs along a line, rather than at a point as with traditional point traps, the method provides the ability to handle extended biomolecules directly. We also carry out a detailed numerical analysis that relates the near-field optical forces to release kinetics. We believe that the architecture demonstrated here will help to bridge the gap between optical manipulation and nanofluidics.

Giant resonant light forces in microspherical photonics

“…The propelling velocity normalized by the incident power has been found to be below ,1 mm s 21 W 21 for dielectric microspheres with diameters (D) from 2 to 20 mm. [20][21][22][23][24][25] Propelling efficiencies can be increased for strongly absorbing particles. 26 However, in the later case, the dominant mechanism of propelling has been attributed to the photophoretic forces occurring due to non-uniform heating of the light-absorbing particle.…”

“…The propelling of dielectric microspheres was studied in liquid-immersed evanescent couplers based on dielectric waveguides, [20][21][22][23] tapered fibers 24 and prisms. 25 The light pressure in such structures and devices is determined by the conservation of the total momentum along the propagation direction.…”

Finite-Boundary Bowtie Aperture Antenna for Trapping Nanoparticles

“…With the optical near-field consisting mainly of exponentially decaying evanescent waves, we can expect steep intensity gradients to be generated at the near-field [18]. It is possible to exploit this extraordinarily steep gradient for optical trapping, which is widely employed in both biology and physics due to its capability to precisely and noninvasively manipulate micron-sized and nanoscale particles (ranging from atoms and molecules to living cells and viruses [19][20][21][22]). …”

Optical trapping of nanoparticles on a silicon subwavelength grating and their detection by an ellipsometric technique

“…A new technique can trap a large number of DNA strands using localized evanescent light [6] . However, a large volume is required to trap many nanoparticles [7] .…”