Pcie 6321

Photoreceiver signals are continuously acquired for 1 minute at 500 kHz using a PCI express data acquisition card (PCIe-6321, National Instruments) and successively analyzed offline using a custom Matlab script. Before analysis, the acquired signal is filtered with a low-pass filter with 20 kHz cut-off frequency to remove high frequency noise. Successively, the signal is segmented into signal events containing single events using a peak-finding procedure. Data are selected and gated using the bivariate distribution f_θvs. average intensity (cf. Fig. S5 of the ESI†). Coincidences, i.e. the simultaneous presence of 2 or more particles in the measurement region, yield signals with higher intensities which are discarded by thresholding. Coincidences were on average ∼13% of total events measured, but could potentially be recovered by using a more sophisticated signal analysis (e.g. a Bayesian approach^{46 (link)}) to increase system throughput. The start/end points of each event are determined as the first and last time-points where the signal crosses a threshold (3 standard deviations of the baseline noise). A fast-Fourier transform (FFT) is used to compute the frequency power spectrum, and peak-finding is used to find the angular oscillations frequency peak. Single-shell theoretical Mie scattering profiles are computed using Matlab MieScat package.⁴⁷

Axopatch 200B (Molecular Devices LLC) was used for electrical measurements. A PCIe-6321 (controlled through a custom LabVIEW script (version 2016, National Instruments)) connected to a BNC 2110 (National Instruments) was used to digitize the output for I–V measurements. Signal digitization was carried out using a Digidata 1440A (Molecular Devices LLC) for translocation experiments. Current traces were acquired at a sampling frequency of 250 kHz and lowpass filtered at 10 kHz using the in-built Bessel filter of the Axopatch 200B.