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ElectroPen: An ultra-low–cost, electricity-free, portable electroporator

Fig 2

High-voltage output of the ElectroPen for electroporation.

(a) Piezoelectric output from the ElectroPen is produced in the form of an exponentially decaying wave (the optimal waveform for electroporation of E. coli cells [17],) achieving an average peak voltage output of Vmax = 2 ± 0.3 kV and time constant τ = 5.1 ± 0.9 ms. The average curve is calculated from n = 38 firings by 3 users (smoothed using a Lowess regression model with a span of 12%), with the shaded area indicating the standard deviation. The raw unsmoothed data for all the outputs are provided in S12 Fig. V0 indicates the average initial value of the waveforms, and the time constant is defined as the time taken for the waveform to decay from its peak voltage to one-third of its peak voltage. This data set was obtained using the Handi lighter (Fayco Industries, New Brunswick, NJ, USA; same lighter used to conduct trials for Fig 4A and 4B). (b) The maximum voltage and time constant outputs produced by the ElectroPen are within the range of commercial electroporators (optimized for E. coli) [18]. From [18], the recommended field strength range is 12–25 kV/cm, and the corresponding peak voltages are 1.2–2.5 kV (for a 0.1-cm arc gap). The optimal time constant range has also been indicated as between 4–6 ms. Data represent n = 38. (c) Average peak voltage produced by different brands of lighters, demonstrating the range of values possible by purchasing lighters from different companies. Data represent n = 4, 3, 4, 3, and 38, respectively. (d) Average time constants produced by different brands of lighters. Data represent n = 4, 3, 4, 3, and 38, respectively. For c and d, n ≥ 3 measurements are used for each brand, and the lines represent the median of the data set; the edges of the box represent the quartiles, with the bottom representing 25th and top representing 75th percentiles; the whiskers extend to the most extreme data points not considered outliers; and for normally distributed data, whiskers correspond to approximately ±2.7σ, where σ is the standard deviation. The data for a, b, c, and d can be found on GitHub under the S1 Data file, under the sheets titled Fig 2A, 2B and 2C and 2D, respectively.

Fig 2

doi: https://doi.org/10.1371/journal.pbio.3000589.g002