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

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

doi:10.1038/s41598-019-45399-2

Victor C Diculescu, Nicoleta G Apostol + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-45399-2

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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.

Highlights

The steep development in information and communication technologies, which includes small and powerful portable devices and ubiquitous broadband communication, opened up new pathways in personalized healthcare[1]
Wearable health monitoring devices are already available on the market[14], a fully wearable skin placed sensor which can read information ranging from temperature to sweat composition or electrical signals is not easy to develop[15] Sensors based on electrical measurements are among the most difficult to build since the electrodes they incorporate should be biocompatible, of low mass and highly flexible or even foldable[15,16]
The Au/Poly(methyl methacrylate) (PMMA) fibers were thermally attached onto flexible Polyethylene terephthalate (PET) substrates in order to obtain the Au/PMMA/PET electrodes. pH sensors were obtained through the electrochemical deposition of Pd metal on the Au/PMMA/PET

Summary

Introduction

The steep development in information and communication technologies, which includes small and powerful portable devices and ubiquitous broadband communication, opened up new pathways in personalized healthcare[1]. The morphology of the electrospun fibers before and after sputtering the Au and after electrochemical deposition of the Pd layer or thermal treatment for the formation of PdO was investigated by scanning (SEM) and transmission electron microscopy (TEM). The open circuit potential (OCP) values of the PdO/Pd/Au/ PMMA/PET pH sensor were measured vs the saturated calomel reference electrode (SCE) until stable values were recorded.

Results

Conclusion