Trapping and actuation of a single nanoparticle using nano-dielectrophoresis and label-free read-out Jacco Ton 1 , Dr. Théo Travers 1 , Prof. Dr. Michel Orrit 1 , Dr. Sergii Pud 2 1 Leiden University, Netherlands, 2 MESA+ Institute for Nanotechnology, University of Twente, Enschede Single-molecule optical methods can discern the behavior of proteins that would be hidden in ensemble-averaged measurements. However, to isolate the signal from a single protein, most methods use chemical labeling and tethering, which can change the proteins’ properties. Therefore we develop a label- and tether-free trapping and interrogation method. We use dielectrophoresis (DEP) for the trapping, and combine it with scattering as optical read-out. DEP can be used to trap a particle in a liquid, using its polarizability in a radio-frequency AC field. As a proof-of-concept, we trapped and actuated a 40 nm polystyrene sphere. For this we use gold nano- electrodes with sub-50 nm gaps, making it possible to use AC voltages lower than 2 V. When a particle is trapped an actuation spectroscopy protocol is applied to the DEP settings. This protocol moves the analyte by trapping and temporarily releasing it at a range of pre-defined frequencies. This translates into modulation of the measured scattering signal at the applied actuation frequencies. The combined information of the known DEP settings and the phase and amplitude of the scattering can potentially report on mass, charge and polarizability. The control of the frequencies in the optical signal makes it possible to extract the small signal of a nano-scale scatterer from the larger background noise signal. Using this lock-in detection scheme, we can optimize sensitivity to even smaller particles or proteins.
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© The Author(s), 2023
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