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. 2022 Aug 16;2(6):568-575.
doi: 10.1021/acsmeasuresciau.2c00036. eCollection 2022 Dec 21.

A Solid-Contact Reference Electrode Based on Silver/Silver Organic Insoluble Salt for Potentiometric Ion Sensing

Shiyu Gan  1 , Chunxian Liao  1 , Rongfeng Liang  1 , Sanyang Du  1 , Lijie Zhong  1 , Yitian Tang  1 , Tingting Han  1 , Yu Bao  1 , Zhonghui Sun  1 , Yingming Ma  1 , Li Niu  1
Affiliations

A Solid-Contact Reference Electrode Based on Silver/Silver Organic Insoluble Salt for Potentiometric Ion Sensing

Shiyu Gan et al. ACS Meas Sci Au. .

Abstract

Solid-contact ion-selective electrodes are a type of ion measurement devices that have been focused in wearable biotechnology based on the features of miniaturization and integration. However, the solid-contact reference electrodes (SC-REs) remain relatively less focused compared with numerous working (or indicator) electrodes. Most SC-REs in wearable sensors rely on Ag/AgCl reference electrodes with solid electrolytes, for example, the hydrophilic electrolyte salts in polymer matrix, but face the risk of electrolyte leakage. Herein, we report a type of SC-REs based on the silver/silver tetraphenylborate (Ag/AgTPB) organic insoluble electrode. The SC-RE consists of a Ag substrate, a solid contact (AgTPB), and a plasticized poly(vinyl chloride) (PVC) membrane containing the hydrophobic organic salt of tetrabutylammonium tetraphenylborate (TBATPB). The potentiometric measurements demonstrated that the SC-RE of Ag/AgTPB/PVC-TBATPB showed a reproducible standard potential in various electrolytes and disclosed high long-term stability. This SC-RE was further fabricated on a flexible substrate and integrated into all-solid-state wearable potentiometric ion sensor for sweat Cl- monitoring.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Principle and performances for the SC-RE of Ag/AgTPB/PVC-TBATPB electrodes. (a) Basic structure and response principle. (b) Potentiometric measurements for the Ag/AgTPB/PVC-TBATPB electrodes (n = 5) in a LiCl electrolyte under the concentration range of 10–5 to 10–1 M as an example. The numbers on the curves represent the logarithms of the electrolyte concentrations. The inset shows the schematic of fabricated SC-RE. (c) The potential responses for the SC-RE in different electrolytes. The EMF is shown in an offset model along the y-axis. (d) Interferences tests of light, gas, and redox couples. The potential measurements for gas and light were carried out in 0.1 M NaCl.
Figure 2
Figure 2
Potential responses for the Ag/AgTPB/PVC-TBATPB electrodes (n = 5) in (a, b) different electrolytes with the same concentration and (c, d) in randomly selected types and concentrations of electrolytes. The EMF in (b) is shown in an offset model along the y-axis.
Figure 3
Figure 3
Water-layer and stability measurements. (a) Water-layer tests for the Ag/AgTPB/PVC-TBATPB electrodes (n = 6). (b, c) The long-term stability was examined in both 0.1 M NaCl and deionized (DI) water. The EMF is shown in an offset model along the y-axis. The EMF in the general non-offset model is shown in Figure S4.
Figure 4
Figure 4
Potentiometric measurements of flexibility Ag/AgTPB SC-RE. (a) Photo image of Ag/AgTPB/PVC-TBATPB under no bending and 60 and 90° bending. (b–d) Scanning electronic microscopy (SEM) images of Ag/AgTPB/PVC-TBATPB under different bendings. (e–g) Potentiometric measurements in different electrolytes under different bendings (n = 3). The EMF is shown in an offset model along the y-axis.
Figure 5
Figure 5
Wearable potentiometric Cl– sensing. (a) Photo image of the potentiometric Cl– sensor chip integrated with a Cl– indicator electrode of a bare Ag/AgCl electrode and SC-RE of Ag/AgTPB/PVC-TBATPB. (b) On-body sweat Cl– measurements (n = 3). (c) Ex situ analysis for sweat Cl– by ion chromatography. The sweat was collected after cooling down. (d) Comparison of testing results between the wearable sensor and ion chromatograph. (e) Potentiometric calibration curves for the Cl– sensor before and after sweat measurements.
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