Scientific Reports (Jun 2019)

Palladium/palladium oxide coated electrospun fibers for wearable sweat pH-sensors

  • Victor C. Diculescu,
  • Mihaela Beregoi,
  • Alexandru Evanghelidis,
  • Raluca F. Negrea,
  • Nicoleta G. Apostol,
  • Ionut Enculescu

DOI
https://doi.org/10.1038/s41598-019-45399-2
Journal volume & issue
Vol. 9, no. 1
pp. 1 – 12

Abstract

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Abstract The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors’ working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. −59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to −28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/°C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.