Plasmonic tweezers: Towards nanoscale manipulation.

• Non-invasive and contactless manipulation techniques enable us to measure the physical properties of living cells and organisms. • Optical tweezers are indispensable tools for contactless and non-invasive manipulation of micro-scale objects. • Trapping nanoscale objects becomes feasible by exploiting surface plasmons to confine the light beyond the diffraction limit. • Plasmonic tweezers are suitable for particle trapping and positioning with an extremely high spatial accuracy. • Plasmonic tweezers based on their geometries can be classified into tweezers based on either the propagating or localized surface plasmons. Reconfigurable plasmonic tweezers realize dynamic control over the position of the plasmonic hotspots and the shape of the trapping potential landscape. Amongst the most promising structures are plasmonic tweezers with built-in light sources, tunable, and mobile plasmonic tweezers. Since their invention in 1986, optical tweezers have become indispensable tools for contactless and non-invasive manipulation of micro and nano-objects. However, the diffraction limit hinders the trapping of nanoscale particles, as the optical gradient force scales with the third power of the particle radius. Trapping of nanometer and sub-nanometer-sized particles becomes feasible by exploiting surface plasmons to confine the light beyond the diffraction limit. Due to the sub-wavelength confinement of light, plasmonic tweezers are fit for particle positioning with an extremely high spatial accuracy. Moreover, by engineering the geometry of the plasmonic nanostructures, one can reconfigure the trapping-potential landscape. Herein, we review the recent developments in the area of plasmonic tweezers. In doing so, we discuss various types of plasmonic tweezers introduced so far and highlight their differences concerning their structures, materials, and functionalities. We finally review some of the most promising advances that would determine the future direction in this field of research, such as tunable and mobile plasmonic tweezers and tweezers with built-in light sources. [ABSTRACT FROM AUTHOR]