The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

Abstract

An electrical measurement is non-linear when it is affected by the applied stimulus, i.e. when the measured phenomenon changes with amplitude. If pinched hysteresis loops can be observed in the voltage current representation, the underlying tissue can be classified as a memristor. Several biological memristors have been published, like human skin and apples. However, changes in the polarization impedance of electrodes may also cause pinched hysteresis loops. The question whether the reported biological memristors are real or whether the results just reflect changes in the polarization impedance arises. If the impedance of the measured object is close to or smaller than the polarization impedance of the used electrodes, the latter may dominate the measurement. In this study, we investigated the non-linear electrical properties of silver/silver chloride electrodes in a sodium chloride solution that has a similar concentration as human sweat and compared these to results from human skin. First of all, we found that silver/silver chloride electrodes in sodium chloride solution can be classified as memristors. However, the currents obtained from the sodium chloride solution are much higher than the currents recorded from human skin and there is a qualitative difference in the pinched hysteresis loops in both cases. We can conclude that the non-linear electrical measurements with silver/silver chloride on human skin are actually dominated by the skin and we can confirm that the human skin memristor really exists.

Bioderived materials for stimuli-responsive, adaptive, and neuromorphic systems: A perspective

“…[60][61][62] The intact living tissues shown to exhibit memristance are complex in comparison to manmade systems and may have multiple sources contributing to their observed i-v relationships, including intrinsic mechanisms enabled by potassium channel activity 171 as well as extrinsic electrochemical interactions with the electrodes. 146 As a result, the electrodes in bioderived systems exhibiting intrinsic mechanisms of memristance play different roles in the operation of the device, but are not the source for resistive switching and memory.…”

“…144,145 Despite good progress, the mechanisms driving observed current-voltage responses within these various organisms is yet to be fully understood. In human skin, the sweat-duct explanation was put forth, 116 and later, the electrode material was found to be important 146 despite the skin still being the dominating factor. Similarly, electrodes interfacing with decellularized plant material could show pinched hysteresis, suggesting redox chemistry plays are marked role, counter to the claim that ion channels dominate within plant tissue.…”

All Pinched Hysteresis Loops Generated by (α, β) Elements: in What Coordinates They May be Observable

“…The pinched hysteresis that accompanies the deformations of inelastic materials and the cyclic stress of buildings simulating an earthquake are documented in [16]. Works from the area of organic and inorganic nature model the memory effects in gases [17], in cylindrical protein polymers (microtubules) [18], in nanofluidic [19] and quantum [20] memristors, in synaptic junctions [21], in hafnium oxide-based ferroelectrics [22], in solutions with measuring electrodes [23], in muscle fibers [24], in human skin [25], or in the behavior of plants and primitive organisms [26], [27] with the utilization of the (-1,-1) element, i.e. the memristor.…”