Electrical Sensing of Au Nanoparticles Manipulated by an Optical Vortex

Recently, electrical sensing techniques of single small objects, such as nanoparticles, viruses, and biomolecules, have attracted much attention. However, fine-tuning of a sensing section is required to achieve high throughput and high precision. Herein, we propose a novel method to improve the measurement accuracy of electrical signals using a double-nanoslit structure exposed to an optical vortex. A small Au particle with a diameter of 200 nm dispersed in a phosphate-buffered saline solution is optically trapped and manipulated in an orbit of 2.3 mu m in diameter at the nanoslit structure. This orbital motion enables us to repetitively sense electrical signals of a small Au particle. As a result, an electrical response of a few hundred picoamperes within some tens of milliseconds is finely shaped removing noise. This result may provide a promising technique for the identification of single target objects at the nanoscale.