Multipass Resistive-Pulse Observations of the Rotational Tumbling of Individual Nanorods

Abstract

Rotational tumbling of nanorods as they translocate through a glass nanopipet modulates the flux of charge carrying ions, generating a resistive pulse with multiple peaks. The measured times between maxima and minima in the resistive pulse correspond to an average rotation of approximately 90° and can be used to compute the rotational diffusion coefficient, Dr. Analytical expressions for the rotational diffusion coefficient (Dr) in terms of the nanorod length (L) allow the calculation of the rod length. We report experiments in which an individual Au nanorod (nominal length of 77–122 nm) is driven repeatedly through the nanopipet orifice by voltage switching at up to 30 Hz, allowing rapid measurement of Dr and L of individual nanorods with ∼15% error. Measured values of Dr between 2000 and 4000 rad2 s–1 for Au nanorods of 77–122 nm length are in good agreement with theoretical predictions.