Paper-Based Metal Electrode Testing - "Tantalum Films in Biosensing Applications"

Figure 1 Wireless device with paper-based metal electrodes

As a reference electrode, a silver/silver chloride ink was pasted on a paper-based electrode with a silver thin film, and then heated at 120 °C for 2 h in ambient air. During the measurement, absorbent cotton (5-10 mm in diameter) was placed on the working and reference electrodes to retain the sample solution. 100 μl of the sample solution was added dropwise to the absorbent cotton on both electrodes. Each type of paper-based metal electrode was connected to a wireless interface potential detector (IPD), and a real-time wireless monitoring system was used to measure the interfacial potential change (μVout) between the solution and the electrode surface.

 Figure 2. Electrical properties of non-bending paper-based metal electrodes obtained wirelessly

(a) Using a paper-based electrode with a tantalum film, the interfacial potential varies from 4.01 to 9.18 with pH. pH sensitivity calibration curve based on (a). The number of measurements was five. (c) Interfacial potential detected using a paper-based electrode with an FPS-based Na-ion-sensitive membrane as a function of Na-ion concentration from 5 to 500 mm. The pNa sensitivity calibration curve based on (c). The number of measurements was five. pNa response of paper-based electrodes and FPS-based sodium-sensitive membranes in 100 mM potassium ion buffer. In (a) and (b), the interfacial potential at pH 9.18 is offset to zero. In (c) and (d), the interfacial potential shift at 5 mM Na+ is zero. In (e), the interfacial potential shift at 5 mM Na+ and 100 mM K+ is zero.

Figure 3 Wirelessly obtained electrical properties of curved paper-based metal electrodes

(a) Photographs of polyvinyl chloride resin based cylinders with different radii (r) from 6.5 to 25 mm. The paper-based electrodes with FPS-based sodium-sensitive membranes used in (b), (c), and (d) were wound on a cylinder with a minimum radius of 6.5 mm (top right photo). (b) μVout is monitored in real time using a paper-based electrode and an FPS-based sodium-sensitive membrane rolled around a cylinder with a minimum radius of 6.5 mm (0 cycle lifetime). (c) The lifetime of a paper-based electrode with an FPS-based Na-ion-sensitive membrane wound on a cylinder with a minimum radius of 6.5 mm. Changes in pNa sensitivity were assessed from 0 to 4 weeks. The number of times of each measurement is three. (d) Detecting changes in pNa sensitivity with a radius of curvature from 6.5 to 25 mm using paper-based electrodes and FPS-based sodium-sensitive membranes rolled around each cylinder.

Figure 4 In vitro real-time monitoring of μVout of sweat samples using a paper-based electrode with an FPS-based sodium-sensitive membrane surrounding a minimum radius of 6.5 mm

(a) Cylinder rolling of μVout, the sodium ion concentration in the buffer was varied from 5 mM to 500 mM. After the 10 mm (b) measurement, the sweat sample was added. The pNa sensitivity calibration curve based on (a). Calculate the sodium ion concentration in the sweat sample from the calibration curve. Changes in sodium ion concentration determined by in vivo measurements. The sodium ion concentration was calculated from the calibration curves obtained in (a) and (b). After the time indicated by the arrow, the sodium ion concentration gradually increased.

Fig.5 Scanning electron microscope (SEM) image of paper funded electrode

(a) unmodified, (b) modified with tantalum, (c) modified with tantalum after bending around the cylinder (r=6.5mm)。