Photonic, plasmonic and hybrid nanotweezers for single nanoparticle trapping and manipulation

Trapping and manipulation of matter at micrometer scaled up to a single nanoparticle has assumed a fundamental role for several applications and, particularly, in biomedical environments. Furthermore, trapping of living matter at the nanoscale, such as proteins and DNA sections, allows the study of many diseases and also the investigation of the effects of new drugs on a single pathogen like a virus. Among the several trapping techniques proposed to control the motion of sub-micrometer particles, optically-based methods have demonstrated the highest efficiency. Strong optical forces obtained with low values of optical power and a contact-free manipulation represent the main advantages of optical tweezers, because long trapping time with no risks of damage of the trapped matter can be realized. Integrated optical nanotweezers provide stronger optical forces with a higher trapping efficiency, compared to performance obtained with bulk configurations. In this work, we review the state-of-the-art of nanotweezers proposed for trapping at sub-micrometer and nanoscale. Performance obtained with photonic and plasmonic nanotweezers are discussed, with a special emphasis on the hybrid photonic/plasmonic nanodevices that allow very strong light-matter interaction (Q/V > 106 (λ/n)-3) with clear advantages for trapping efficiency at the nanoscale.