The viscosity response behavior of bare nanopipettes based on ionic current rectification

In this paper, bare nanopipettes perfused with low-viscosity electrolyte solutions achieved ionic current rectification (ICR) response capabilities to solution viscosity, providing a simple method for fabricating nanopipette viscosity probes. The ICR phenomenon was investigated in four different viscosity configurations and the viscosity response mechanism of the nanopipette was explained by the effect of the electric double layer and electroosmotic flow on the conductivity of the nanopipettes' tip. The viscosity response sensitivity was improved by optimizing influencing factors such as KCl concentration, pH, and nanopipette diameter. Data fitting showed that within the viscosity range from 0.91 mPa.s to 40.07 mPa.s, the rectification ratio of the nanopipettes has a good linear relationship with the solution viscosity (r = 0.04η - 0.02). Additionally, the bare nanopipettes exhibit good reversibility and selectivity in viscosity response and also demonstrate the potential for use in single-cell cytoplasmic viscosity detection. The viscosity response behavior of bare nanopipettes provides important insights for constructing cytoplasmic viscosity probes, which will expand the applications of nanopipettes in cytoplasmic detection.