Non-invasive measurement of normal skin impedance for determining the volume of the transdermally extracted interstitial fluid

• An equipotential method was proposed to measure the normal skin impedance.
• The impedance aimed at determining the volume of extracted interstitial fluid.
• The method was verified by experiment comparing to the implanted electrode method.
• The effects of humidity and pressure on the measurement accuracy were studied.

Normal skin impedance, which has a good correlation with skin permeability, can be used to calculate the volume of extracted interstitial fluid. However, it is still very difficult to determine non-invasively the normal skin impedance. In this study, a novel non-invasive method based on equipotential theory for real-time, in vivo and accurate measurements of normal skin impedance was proposed. The suggested method was based on the theory of an equipotential between the saliva and interstitial fluid of an organism, and this method was compared with the method based on an implanted electrode. The effects of humidity and pressure on the measurement accuracy of normal skin impedance were also studied. The feasibility of this method was verified by the results of the experiments. The proposed method is expected to enhance the blood glucose prediction accuracy and demonstrates a huge significance for the minimally invasive measurements of blood glucose in clinical application.