Cation dependence of noise induced by polymer adsorption in nanopores Anna M. Drummond Young , Stuart F. Knowles, Alice L. Thorneywork University of Oxford, United Kingdom Nanopores underpin single molecule sensing techniques at the cutting edge of biotechnological measurement. In these techniques, a nanopore is immersed in an electrolyte and a potential difference is applied across the pore so that a current flows through it. Understanding and controlling transport properties in these systems, including fluctuations or noise in the current, is central to the further development of nanopore technologies. Polymers are often added to nanopore systems to improve pore functionality, for example by modifying electrokinetic effects or passivating surfaces. It has previously been observed that for potassium chloride solutions the addition of polyethylene glycol (PEG) creates excess noise in the current trace, which has a characteristic shape and frequency range [1] . This excess noise has been attributed to the process of PEG adsorption and desorption from the walls of the nanopore; the shape of the noise spectrum has been used to infer details of the adsorption potential. Here, we investigate how the choice of group 1 cation used in the electrolyte in quartz glass nanopores affects fluctuations in the ionic current linked to polymer adsorption. Noise in the current was measured with and without PEG for four different group 1 chlorides: sodium chloride, lithium chloride, caesium chloride, and rubidium chloride, and the noise was quantified by calculation of its power spectral density. In NaCl, LiCl, and CsCl, excess noise with the same shape and frequency range as KCl was observed, but no excess noise was observed in the case of RbCl. Previous studies have suggested that PEG adsorption [2] and electro-osmotic flow in conical nanopores [3] is cation dependent, although these studies do not single out differences with rubidium. Our findings suggest that while for Na + , Li + , and Cs + PEG adsorption in glass nanopores is comparable to K + , in the case of Rb + there are qualitatively different fluctuations in the current resulting from the adsorption or desorption of PEG from the surface. References 1. Knowles, S. F. et al. Current fluctuations in nanopores reveal the polymer-wall adsorption potential. Phys. Rev. Lett. 127, 137801 (2021). 2. Chai, L., Goldberg, R., Kampf, N. & Klein, J. Selective adsorption of poly (ethylene oxide) onto a charged surface mediated by alkali metal ions. Langmuir 24, 1570–1576 (2008) 3. Mc Hugh, J., Andresen, K. & Keyser, U. F. Cation dependent electroosmotic flow in glass nanopores. Appl. Phys. Lett. 115, 113702 (2019).
P05
© The Author(s), 2023
Made with FlippingBook Learn more on our blog