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Abstract Nearly all biosensing platforms can be described using two fundamental steps—collection and detection. Target analytes must be delivered to a sensing element, which can then relay the transduced signal. For point-of-care technologies, where operation is to be kept simple, typically the collection step is passive diffusion driven—which can be slow or limiting under low concentrations. This work demonstrates an integration of both active collection and detection by using resonant wireless power transfer coupled to a nanogap capacitor. Nanoparticles suspended in deionized water are actively trapped using wireless dielectrophoresis and positioned within the most sensitive fringe field regions for wireless impedance-based detection. Trapping of 40 nm particles and larger is demonstrated using a 3.5 V_RMS, 1 MHz radiofrequency signal delivered over a distance greater than 8 cm from the nanogap capacitor. Wireless trapping and release of 1 µm polystyrene beads is simultaneously detected in real-time over a distance of 2.5 cm from the nanogap capacitor. Herein, geometric scaling strategies coupled with optimal circuit design is presented to motivate combined collection and detection biosensing platforms amenable to wireless and/or smartphone operation. 

Nanoscale plasmonic gaps are useful structures both electrically, for creating quantum tunnel junctions, and optically, for confining light. Inelastic tunneling of electrons in a tunnel junction is an attractive source of light due to the ultrafast response rate granted by the tunneling time of electrons in the system as well as the compact dimensions. A main hurdle for these light emitting tunnel junctions, however, is their low external efficiency given by both low electron-to-plasmon conversion as well as low plasmon-to-photon conversion. Inversely, coupling light into a nanogap for high confinement and field enhancement can be difficult due to the size mismatches involved. We show a 3 nm gap metal-insulator-metal plasmonic tunnel junction evanescently coupled to the fundamental TE mode of a standard silicon waveguide in a tapered directional coupler configuration with a transmission efficiency of 54.8% atλ =1.55μm and a 3-dB coupling bandwidth of 705 nm. In the inverse configuration, we show an electric field enhancement of |E|/|E₀| ≈120 within a plasmonic tunnel junction in the technologically important optical telecommunications band.