Optical Determination of Silicon Nanowire Diameters for Intracellular Applications

Silicon nanowires (SiNWs) are an important class of materials for biomedical and electronics applications, with the nanowire diameter playing a fundamental role in device functionality. Here we present a method, based on light scattering intensity and ensemble electron microcopy (EM) measurements, that allows for a precise optical determination of a specific NW’s diameter within an accuracy of a few nanometers (4.8 nm), an error of only ∼8.0%. This method takes advantage of the strong dependence of optical scattering on SiNW diameter to construct an optical to EM transform, with Lorentz-Mie theory showing that this method can be used for NWs up to ∼150 nm in diameter. Additionally, this technique offers some potential insights into biophysical interactions, allowing the optical calibration of individual intracellular SiNW force probes, enabling a ∼100-fold improvement in experimental uncertainty. Using these probes, we were able to measure drug-induced vasoconstriction in human aortic smooth muscle cells (HASMCs), which exerted ∼171 pN of force after ∼30 min of exposure to the hormone angiotension II. These findings represent a scalable method for characterizing SiNW-based devices that are easily extendable to other materials and could be of use in ensuring quality control for future photovoltaics, optical sensors, and nanomaterial biosensors.