Nanoscale Surface Charge Visualization of Human Hair

Abstract

The surface charge and topography of human hair are visualized synchronously at the nanoscale using scanning ion conductance microscopy (SICM), a scanning nanopipette probe technique that uses local ion conductance currents to image the physicochemical properties of interfaces. By combining SICM data with finite element method (FEM) simulations that solve for ion transport at the nanopipette under bias, one is able to quantitatively correlate colocated surface charge and topography. The hair samples studied herein, from a 25-year-old Caucasian male with light hair (as an exemplar), reveal that untreated hair, in areas ca. 1 cm from the root, has a fairly uniform negative charge density of ca. −15 mC/cm–2 (in pH 6.8 aqueous solution), with some higher magnitude negative values localized near the boundaries between hair cuticles. Common chemical treatments result in varying degrees of charge heterogeneity. A bleach treatment produces some highly negatively charged localized regions (−80 to −100 mC/cm–2 at pH 6.8), due to hair damage, while a chemical conditioner treatment causes an overall increase in the homogeneity of the surface charge, together with a shift in the surface charge to positive values. Bleached surfaces are temporarily repaired to some extent through the use of a conditioner, as judged by the surface charge values. Finally, SICM is able to detect differences in the surface charge density of hair at different distances from the root (equivalent to hair age). Presently, the assessment of hair surface charge mainly relies on zeta-potential measurements which lack spatial resolution, among other drawbacks. In contrast, SICM enables quantitative surface charge mapping that should be beneficial in deepening understanding of the physicochemical properties of hair and lead to the rational development of new treatments and the assessment of their efficacy at the nanoscale. Given the widespread interest in the surface charge properties of interfaces, this work further demonstrates that SICM should generally become an important characterization tool for surface analytical chemists.

Coarse-grained molecular models of the surface of hair

“…The shape of the damage patterns is qualitatively similar to that observed in previous AFM experiments. 23,28,43 Similar coverage surface coverage projections are also observed for water and n-hexadecane (Fig. 2 in the ESI) † .…”

“…14 The outer layers of hair are of particular interest since adsorption of formulation components, as well as lubrication between hair fibres, will largely depend on its surface properties. 1 Experimental surface characterization of virgin and damaged human hair has included the measurement of wetting by means of liquid contact angles, [15][16][17][18][19][20] surface charge density [21][22][23] as well as surface topography and friction using the atomic force microscope (AFM) 8,20,24,25 and high-load nanotribometers. 26 These studies have shown that compared to virgin hair, damaged hair usually displays increased surface charge density, hydrophilicity, and friction.…”

[Retracted] Application of Compound Control Method Based on WOA in Micropositioning Stage of SICM

“…Scanning ion conductance microscopy (SICM) [1], as a member of the scanning probe microscope (SPM) [2], has been developing for thirty years since 1989 and applied to many areas, such as surface topography measurement [3], nanoscale operation [4], cell volume measurement [5], cell mechanical properties research [6], and cell dynamics research [7]. It has been widely used in life science, medicine, materials science, nanofabrication, and other fields.…”

Scanning ion conductance microscopy reveals differences in the ionic environments of gram positive and negative bacteria

“…The current magnitude is highly sensitive to nanopipette-substrate separation and local ion conductivity, including that arising from the double layer at charged interfaces, and can be used to probe (independently) topography and surface charge of a range of substrates. [13][14][15] Critical information about the ionic environment of the substrate -solution interface can be acquired by employing specific potential-time SICM scanning protocols, 16,17 in tandem with finite element method (FEM) simulations, as exemplified by the quantitative analysis of surface charge 15,16,[18][19][20] and for reaction mapping. 12,21 In this paper, we consider the use of SICM to characterize the ionic (bioelectrical) environment of single live bacterial cells.…”