Temporary Tattoo pH Sensor with pH-Responsive Hydrogel via Initiated Chemical Vapor Deposition

Katrin Unger*, Francesco Greco, Anna Maria Coclite

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


In the expanding field of physiological pH skin sensors, thin temporary tattoo-based devices have gained attention because of ultra-conformal adhesion while providing excellent water vapor transmission. Here, a pH sensor tattoo made of temporary tattoo paper, screen-printed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate electrodes, and pH-responsive hydrogel deposited via initiated chemical vapor deposition, is proposed. The tattoo sensor is easily transferred on skin, maintaining full functionality, and shows excellent conformability to topographical features of epidermis. The investigation of the morphology of all layers within the sensor verifies full control of the desired width of electrodes, thickness of hydrogel, and deposition shielded areas. The hydrogel layer exhibits a reversible pH-responsive swelling of 24.7 ± 0.3% to 38 ± 1%, with respect to the dry state, at pH 4 to pH 6, respectively. Impedance spectroscopy identifies the phase shift at 10 and 1000 Hz as an excellent pH-related property of the sensor, which can be only ascribed to the presence of the hydrogel. The sensors ability to be operated with non-sophisticated read-out hardware and software is also demonstrated.

Original languageEnglish
Article number2100717
JournalAdvanced Materials Technologies
Issue number5
Publication statusPublished - May 2022


  • Arduino
  • biomonitoring
  • iCVD
  • smart hydrogel
  • wearable device

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Industrial and Manufacturing Engineering

Fields of Expertise

  • Advanced Materials Science


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