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

Abstract

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.

Label-Free Electrochemical Immunosensor Made with Tree-like Gold Dendrites for Monitoring 25-Hydroxyvitamin D3 Metabolite

“…In this regard, miniaturized electrochemical systems, produced for example by screen printing and 3D printing methods, are promising for precision nutrition management as they can monitor health indicators in situ in a noninvasive or minimally invasive way. − In addition, they allow measurements with small sample volumes, being user-friendly to operate. Screen-printed electrodes can be manufactured on various substrates such as plastic, on the skin as a tattoo, and on surfaces such as gloves and mouthguards; moreover, they may be customized with their versatility in terms of size and geometry. − Electrochemical biosensors, including HRP-labeled biosensors, have been used for monitoring 25­(OH)­D3 (see Table ). However, there are no commercial hand-held devices for real-time and on-site monitoring.…”

Universal Fully Integrated Wearable Sensor Arrays for the Multiple Electrolyte and Metabolite Monitoring in Raw Sweat, Saliva, or Urine

“…Then, the sweat Na + proceeded through two stages: a steady level between 14.8 and 25.2 min, which is presumably because of the continual resistance ride-caused steady sweat rate and a sudden rise beginning at 25.2 min, which could be driven by the raised Na + level in blood . In the interim, the pH in sweat kept relatively stable at ∼4.63 in the whole process (Figure C), which is within the physiological range of sweat from healthy human subjects . For the sweat UA, a downward tendency is found during the cycling exercise (Figure D), which could be due to the massive sweat secretion .…”

Advances in surface modification and functionalization for tailoring the characteristics of thin films and membranes via chemical vapor deposition techniques

“…iCVD is one of the most attractive variations of CVD in which a precursor is introduced to the CVD chamber at low pressures and relies on the use of a radical initiator that can be thermally activated at low temperatures and preserving the functionality of the precursor 138,139 . A free‐radical polymerization occurs between the radicals formed by initiator decomposition and monomer species 16 .…”

“…[135][136][137] 4.9 | Initiated CVD iCVD is one of the most attractive variations of CVD in which a precursor is introduced to the CVD chamber at low pressures and relies on the use of a radical initiator that can be thermally activated at low temperatures and preserving the functionality of the precursor. 138,139 A free-radical polymerization occurs between the radicals formed by initiator decomposition and monomer species. 16 During the deposition, substrate is kept at room temperature which is advantageous in utilization of all kinds of substrates including polymeric membranes.…”