Near-field Optical Manipulation Research Articles

Plasmofluidic-Based Near-Field Optical Trapping of Dielectric Nano-Objects Using Gold Nanoislands Sensor Chips.

Near-field optical manipulation has been widely used for guiding and trapping nanoscale objects close to an optical-active interface. This near-field manipulation opens opportunities for next-generation biosensing with the capability of large-area trapping and in situ detection. In this article, we used the finite element method (FEM) to analyze the motion mechanism of nano-objects (50-500 nm) in the near-field optics, especially localized surface plasmon resonance (LSPR). The size-dependent optical forces and hydrodynamic forces of subwavelength nanoparticles (<500 nm) in different hydrodynamic velocity fields were calculated. When the strength of the local electric field was increased, LSPR with two-dimensional gold nanoislands (AuNIs) showed improved capability for manipulating nano-objects near the vicinity of the AuNI interface. Through the experiments of in situ interferometric testing 50-500 nm nano-objects with constant number concentration or volume fraction, it was confirmed that the local plasmonic near-field was able to trap the dielectric polystyrene beads smaller than 200 nm. The plasmofluidic system was further verified by testing biological nanovesicles such as exosomes (40-200 nm) and high- and low-density lipoproteins (10-200 nm). This concept of direct dielectric nano-objects manipulation enables large-scale parallel trapping and dynamic sensing of biological nanovesicles without the need of molecular binding tethers or labeling.

Plasmonic optical tweezers based on nanostructures: fundamentals, advances and prospects

Abstract The ability of metallic nanostructures to confine light at the sub-wavelength scale enables new perspectives and opportunities in the field of nanotechnology. Making use of this unique advantage, nano-optical trapping techniques have been developed to tackle new challenges in a wide range of areas from biology to quantum optics. In this work, starting from basic theories, we present a review of research progress in near-field optical manipulation techniques based on metallic nanostructures, with an emphasis on some of the most promising advances in molecular technology, such as the precise control of single biomolecules. We also provide an overview of possible future research directions of nanomanipulation techniques.

Nano-Particle Manipulated with Near-Field Optical Tweezers

By applying the direct calculation of Maxwell stress tensor using three-dimensional finite difference time domain method, the feasibility of using a metal-coated fiber probe to create near-field optical tweezers is investigated. Numerical results indicate that these schemes are able to trap nano-particles with lower laser intensity than that required by conventional optical tweezers. The near-field optical trapping systems that are more flexible than conventional optical tweezers are built. In experiments, 120-nm polystyrene particles are trapped in a multi-circular shape with a minimum size of 400 nm. The realization of trapping particles in the range of tens of nanometers largely promotes the role of near-field optical manipulation at the nanometer scale.

Particles nanomanipulation by the enhanced evanescent field through a near-field scanning optical microscopy probe

A near-field scanning optical microscopy (NSOM) probe and a polarized semiconductor laser (808 nm, cw) were applied to push the trapping resolution down to 120 nm on near-field optical manipulation. A multi-circular shape with a minimum size of 400 nm consisting of 120 nm polystyrene particles can be obtained. They are at a resolution of d ( d: NSOM probe tip diameter) and λ/7 ( λ: laser wavelength), respectively. It is proved that sample concentration and laser power can affect feature size of trapping patterns. In this paper, the effect of trapping forces acted on a nanoparticle along three axis directions on trapping positions is studied, and different trapping positions are generated: the aperture edge in polarization direction and center surface of the probe tip. The result indicates that the single mode NSOM fiber probe is able to trap nanoparticles in a circular shape with lower laser intensity than that required by conventional optical tweezers. The simulated trapping positions around the probe tip based on the conservation law of momentum are found to agree well with experimental results.

Optical micromanipulations in the non‐diffractive regime

The ever-evolving topic of optical micromanipulation has established itself as a discipline over the last three decades, and is of much interest to a wide research community due to constantly emerging new applications across the various key disciplines. Performing optical manipulation using evanescent waves is termed near-field optical manipulation, which is essentially the manipulation of particles in the non-diffractive regime. The concept of the breaking of diffraction limit is the spur driving near-field optics studies, as opposed to all far field optical applications where light cannot be focused to a spot smaller than the diffraction limited value, which is about half the wavelength of light in the medium. The authors present a review of the various near-field optical manipulation techniques and then report on the observation of erythrocyte pearl chains by a near-field optical tweezer.

A virtual optical probe based on evanescent wave interference

A virtual probe is a novel immaterial tip based on the near-field evanescent wave interference and small aperture diffraction, which can be used in near-field high-density optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation of nano-scale specimen, etc. In this paper, the formation mechanism of the virtual probe is analysed, the evanescent wave interference discussed theoretically and the sidelobe suppression by small aperture is simulated by the three-dimensional finite-difference time-domain method. The simulation results of the optical distribution of the near-field virtual probe reveal that the transmission efficiency of the virtual probe is 102-104 times higher than that of the nano-aperture metal-coated fibre probe widely used in near-field optical systems. The full width at half maximum of the peak, in other words, the size of virtual probe, is constant whatever the distance in a certain range so that the critical nano-separation control in the near-field system can be relaxed. We give an example of the application of the virtual probe in ultrahigh-density optical data storage.