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 μm 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.