Printed pH Sensors for Textile‐Based Wearables: A Conceptual and Experimental Study on Materials, Deposition Technology, and Sensing Principles

Abstract

Human biofluids contain numerous known physical and chemical biomarkers that play a vital role in diagnosing the human's health status. In healthy conditions, these biofluids maintain a strict pH balance with an efficient regulation, and slight changes in pH can be used as an early detector of malfunction or disease. Sweat is such a biofluid and normal sweat has a pH in the range of pH 4.5-6.8. [1] It is possible to track dehydration [2,3] or risk of diabetes [4] and detect cystic fibrosis [5] with the pH readings of perspiration/sputum/urine.Similarly, wound healing is a complex dynamic and multifaceted process consisting of hemostasis, inflammation, proliferation, and remodeling stages. [6] During these different stages, the wound fluid pH could vary between 4.5 and 8.5, [7,8] depending on the type of wound and its complexities in healing. A recent report indicates that the wound management expenditure has grown up to 4% of the health budget contribution in Europe. [9] However, with the help of accurate determination of the wound's pH, very essential physiological information can serve as a source to simplify the entire wound diagnosis and treatment practice. [10][11][12] pH is a measure of acidity or basicity, and in 1909, Sørensen defined the pH scale as the H þ ion molar concentration on a negative logarithm scale. [13] In the same year, scientists developed a pH sensitive glass electrode. [14] Arnold Beckman designed the very first commercial pH measurement system in 1936, which brought about the production of commercial pH meters. [15] It consisted of glass electrodes where the potential difference between the working and reference electrodes indicate the analyte's pH. Those sensor systems are highly sensitive to H þ ions and stable, however, they are fragile, bulky and do not have a suitable form factor to be incorporated for human body in situ measurements. pH sensors

Highly Stable and Reusable 3D Graphene-Quinizarin Voltammetric pH Sensor

“…The as-fabricated electrodes are found to be more stable than previously reported anthraquinonesulfonate modified glassy carbon electrodes (2 months), cysteic acid/GO composite film (storage life-1 month), MWCNT/alizarin/Nafion (1 week), and carbon/PANI electrodes which exhibit stable results for 60 min. [60][61][62][63] Additionally, unlike glass bulb electrodes, these electrodes don't require any special storage conditions.…”

Electrochemical biosensors and power supplies for wearable health‐managing textile systems

“…Another way is to fabricate the flexible pH sensor directly based on the textile, the working, reference, and counter electrodes can be integrated into the flexible fabric by utilizing printed electronics techniques such as ultrasonic spray coating and screen printing. [76][77][78] T A B L E 1 A summary of wearable biosensors for real-time biomarkers monitoring. 35.9 mV/dec CNT fiber [53] (Continues)…”

MoS2‐Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

“…On the other hand, lower areal capacitance implies the poor electrical conductivity of electrodes. LIG-PANI 4-9.5 3-4 min 45 [79] TA-RGO 1-10 -53.0 ± 0.7 . The sensitivity was calculated from the slope of the calibration curve which exceeded the Nernst limit of pH sensitivity.…”