• Dervisevic, Esma
• Dervisevic, Muamer
• Voelcker, Nicolas H.
• Esser, Lars

Abstract

Microneedle-based wearable sensors offer an alternative approach to the traditional invasive blood-based health monitoring and disease diagnostics techniques. Instead of blood, microneedle-based sensors target the skin interstitial fluid (ISF), in which the biomarker type and concentration profile resemble the one found in the blood. However, unlike blood, interstitial fluid does not have the same pH-buffering capacity causing deviation of pH levels from the physiological pH. Information about the skin ISF pH levels can be used as a biomarker for a wide range of pathophysiological conditions and as a marker for the calibration of a wearable sensor. The ISF pH can significantly affect the detection accuracy of other biomarkers as it influences enzyme activity, aptamer affinity, and antibody-antigen interaction. Herein, we report the fabrication of a high-density polymeric microneedle array-based (PMNA) sensing patch and its optimization for the potentiometric transdermal monitoring of pH levels in ISF. The wearable sensor utilizes a polyaniline-coated PMNA having a density of ~10,000 microneedles per cm2, containing individual microneedles with a height of ~250 µm, and a tip diameterof ~2 µm. Furthermore, an insulating layer is deposited at the base of the PMNA to avoid interference from sweat. The wearable pH sensor operates from pH 4.0 to 8.6 with a sensitivity of 62.9 mV per pH unit. Ex vivo testing on a mouse demonstrates the ability of the PMNA to provide a real-time reading of the transdermal pH values. This microneedle-based system will significantly contribute to advancing transdermal wearable sensors technology, simplifying the fabrication process, and improving the cost-effectiveness of such devices.

Topics

• density
• impedance spectroscopy
• interstitial
• pH value