Optical Tweezing Terahertz Probing for a Single Metal Nanoparticle.

Recently, extensive research has been reported on the detection of metal nanoparticles using terahertz waves, due to their potential for efficient and nondestructive detection of chemical and biological samples without labeling. Resonant terahertz nanoantennas can be used to detect a small amount of molecules whose vibrational modes are in the terahertz frequency range with high sensitivity. However, the positioning of target molecules is critical to obtaining a reasonable signal because the field distribution is inhomogeneous over the antenna structure. Here, we combine an optical tweezing technique and terahertz spectroscopy based on nanoplasmonics, resulting in extensive controllable tweezing and sensitive detection at the same time. We observed optical tweezing of a gold nanoparticle and detected it with terahertz waves by using a single bowtie nanoantenna. Furthermore, the calculations confirm that molecular fingerprinting is possible by using our technique. This study will be a prestep of biomolecular detection using gold nanoparticles in terahertz spectroscopy.