Thermodynamic Charge-to-Mass Sensor for Colloids, Proteins, and Polyelectrolytes

Abstract

A sensor is introduced that gauges the ratio of charge z to mass m of macro-ions in liquid media. The conductivity is measured in a small volume of salt solution, separated from the macro-ions by a semipermeable membrane. The mobile counterions released by the macro-ions increase the measured salt concentration, from which z/m can be calculated without any adjustable parameter. The charge sensor constitutes a noninvasive method that probes unperturbed macro-ions in a manner that is independent of (the distribution in) macro-ion size and shape. We validate the sensor’s general applicability for three kinds of macro-ions, spanning 2 orders of magnitude in z/m, namely, dextran sulfate, bovine serum albumin, and colloidal silica. Measured z/m values comply for all macro-ion types with independent information on macro-ion surface charge.