Fig. 1: Charge symmetry breaking in neutral PSBMA.

a Chemical formula of PSBMA with positively charged group closer to the chain backbone and the negatively charged group away from the chain backbone. b Titration curve of PSBMA (80 mM in 1 mL of 1 M KCl) showing charge neutrality at the experimental pH range. In the positive configuration of the experimental setup (c), PSBMA does not show any translocation event (d). In the negative configuration of the experimental setup (e), PSBMA exhibits a series of translocation events, behaving like a polyanion (f). g Differential binding of counterions to the positive and negative groups of PSBMA, originating from the gradient of local dielectric constant, causes CSB. h Sketch of the local dielectric constant as a function of the distance away from the chain backbone. In (c–f), solution: 10 nM PSBMA in 1 M KCl buffered at pH 7 with 10 mM HEPES, pore diameter: 3.5 nm, voltage: 100 mV. In (d–f), sampling rate: 250 kHz, low-pass filter frequency: 10 kHz.