Optical hydrogel detector for pH measurements

Yousef Alqurashi, Mohamed Elsherif, Asail Hendi, Khamis Essa, Haider Butt

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Measuring pH has become a major key for determining health conditions, and food safety. The traditional pH assessment approaches are costly and offer low sensitivity. Here, a novel pH sensor based on a pH-responsive hydrogel, has been developed. A Fresnel lens pattern was replicated on the surface of the pH-responsive hydrogel using the replica mold method. The pH-sensors were tested in pH range of 4-7. Introducing various pH solutions to the pH-sensor led to volumetric shifts as the hydrogel swelled with pH. Consequently, the dimensions of the replicated Fresnel lens changed modifying the focal length and the focus efficiency of the optical sensor. As a result, the measured optical power at a fixed distance from the sensor changed with pH. The optical sensor showed the best performance in the acidic region when pH changed from 4.5 to 5.5 in which the recorded power increased by 13%. The sensor exhibited high sensitivity to pH changes with a short respond time in reversible manner. The developed pH-optical sensor may have applications in medical point-of-care diagnostics, and wearable continuous pH detection devices.
Original languageEnglish
Article number40
Issue number1
Publication statusPublished - 13 Jan 2022


  • Fresnel lens
  • hydroxyethyl methacrylate
  • pH-responsive hydrogels
  • sensors


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