Impedance spectroscopy of solutions at physiological glucose concentrations

Abstract

Impedance spectroscopy has been proposed as possible approach for non-invasive glycaemia monitoring. However, few quantitative data are reported about impedance variations related to glucose concentration variations, especially below the MHz band. Furthermore, it is not clear whether glucose directly affects the impedance parameters or only indirectly by inducing biochemical phenomena. We investigated the impedance variations in glucosewater, glucose-sodium chloride, and glucose-blood samples, for increasing glucose values (up to 300 mg/dl). In all the frequency range (0.1-10 7 Hz) glucose-water samples showed impedance modulus increases for increasing glucose values (up to 135%). In blood and sodium chloride samples the impedance modulus showed only slight variations (2% and 1.4%), but again in wide frequency ranges. Therefore: i) glucose directly affects the impedance parameters of solutions; ii) effects are more relevant at frequencies below the MHz band; iii) the influence on the impedance is decreased in high conductivity solutions, but still clearly present.

Dielectric properties of glucose in bulk aqueous solutions: Influence of electrode polarization and modeling

“…Some previous reports proposed a possibility of glucose determination within the physiological range and they explored the region of electrode polarization (Tura et al, 2007;Park et al, 2003). However, no further investigations from those groups have been reported yet.…”

“…One viable approach has been to measure aqueous glucose solutions at much higher frequencies (i.e., in the Megahertz-Gigahertz region), where EP may not pose a problem (Mashimo et al, 1992;Fuchs and Kaatze, 2002;Meriakri et al, 2007). Recent studies have reported that the dielectric properties in the low frequency range (<1 MHz) of certain types of solutions (i.e., glucose/water, glucose/saline, and glucose/blood solutions) changed significantly when glucose concentration levels were varied within the physiological range (Park et al, 2003;Tura et al, 2007). However, those studies did not consider the effect of electrode polarization, leaving in question whether or not the large changes seen in the permittivity of the glucose solutions was due to simple changes in the DC conductivity of the solutions (Caduff et al, 2008;Tura, 2008), which also greatly affects the electrode polarization.…”

Noncontact characterization of glucose by a waveguide microwave probe

“…Amperometric enzyme electrodes hold a leading position among present glucose biosensor systems and have already found a large commercial market. 14 Glucose biosensors have taken several other forms, based on electrochemical, optical, piezoelectrical, thermal or mechanical principles [7][8][9][10][11][12].…”

Reply to comment on experimental methods and conclusions of impedance spectroscopy of solutions at physiological glucose concentrations by A. Caduff, M. S. Talary, Y. Feldman

“…The comment to the manuscript [1] Second criticism to our study is that the measurement probe was not adequate for electro-impedance spectroscopy (EIS), because it was designed for conductivity measurements. It is right that the probe is usually sold coupled with a conductivity meter, but this is not enough to conclude that the probe cannot be used for EIS.…”