Membranes (Mar 2023)

Directly Using Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene for a Solid-Contact Potentiometric pH Sensor toward Wearable Sweat pH Monitoring

  • Rongfeng Liang,
  • Lijie Zhong,
  • Yirong Zhang,
  • Yitian Tang,
  • Meixue Lai,
  • Tingting Han,
  • Wei Wang,
  • Yu Bao,
  • Yingming Ma,
  • Shiyu Gan,
  • Li Niu

DOI
https://doi.org/10.3390/membranes13040376
Journal volume & issue
Vol. 13, no. 4
p. 376

Abstract

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The level of hydrogen ions in sweat is one of the most important physiological indexes for the health state of the human body. As a type of two-dimensional (2D) material, MXene has the advantages of superior electrical conductivity, a large surface area, and rich functional groups on the surface. Herein, we report a type of Ti3C2Tx-based potentiometric pH sensor for wearable sweat pH analysis. The Ti3C2Tx was prepared by two etching methods, including a mild LiF/HCl mixture and HF solution, which was directly used as the pH-sensitive materials. Both etched Ti3C2Tx showed a typical lamellar structure and exhibited enhanced potentiometric pH responses compared with a pristine precursor of Ti3AlC2. The HF-Ti3C2Tx disclosed the sensitivities of −43.51 ± 0.53 mV pH–1 (pH 1–11) and −42.73 ± 0.61 mV pH–1 (pH 11–1). A series of electrochemical tests demonstrated that HF-Ti3C2Tx exhibited better analytical performances, including sensitivity, selectivity, and reversibility, owing to deep etching. The HF-Ti3C2Tx was thus further fabricated as a flexible potentiometric pH sensor by virtue of its 2D characteristic. Upon integrating with a solid-contact Ag/AgCl reference electrode, the flexible sensor realized real-time monitoring of pH level in human sweat. The result disclosed a relatively stable pH value of ~6.5 after perspiration, which was consistent with the ex situ sweat pH test. This work offers a type of MXene-based potentiometric pH sensor for wearable sweat pH monitoring.

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