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Device Technologies and Biomedical Robotics

Device Technologies and Biomedical Robotics - Poster Session D

Poster I18 - Polypropylene Paper-Based Electrodes with a Voltage Reset for pH Sensing

Friday, October 25, 2024

3:30 PM - 4:30 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Gabriella Doan

Undergraduate Student
Southern Methodist University
Dallas, Texas, United States

Co-Author(s)

KC

Khengdauliu Chawang

PhD Student
Southern Methodist University, United States
J.-C. Chiao, PhD

Mary and Richard Templeton Centennial Chair
Southern Methodist University
Dallas, Texas, United States

Introduction: pH as a measure of the concentration of hydrogen ions is crucial to chemical and biological equilibriums. Novel biosensors aim to monitor this value for applications such as food safety and is a widely explored topic. Electrodes made from ion-sensitive, conductive film have demonstrated the prospective benefits of such a method in various biomedical applications. Moreover, processes such as external voltage resets have further supported the use of these sensors. This abstract details the testing methods and initial results of one such film, iridium-oxide (IrOx) on polypropylene paper-based film (PPMM), to produce miniature electrodes for monitoring pH.

Materials and

Methods: Fabricated PPMM film was cut into strips approximately 2 mm by 20 mm. An electrical connection was formed by adhering each strip to copper wire with silver epoxy. This working electrode (WE), a commercial silver/silver chloride reference electrode (RE), and a platinum counter electrode (CE) were employed by a potentiostat device to perform electrochemical tests such as chronoamperometry (CA) and open circuit potential-time (OCPT) measurements in solutions such as universal buffer (UB) and phosphate-buffered saline (PBS).

CA tests, each lasting 2 minutes, were used to “reset” the electrode surface. Reset efficacy on PPMM was determined by drift, defined as the difference between the initial and settled potential of an individual OCPT test. Minimal drift indicates an electrode’s stability. To find the optimal CA voltage, new electrodes were tested in neutral pH 7. Open circuit potential (OCP) was recorded for 20 minutes to find the initial performance. Then, successive CA resets were performed. Each reset was followed by OCP for 20 minutes, the drift for which was determined. The CA reset with the lowest drift was then used to compare with the initial performance (no reset condition).

Settled OCPT cycles performed under the no reset and reset conditions were also compared. One cycle in UB consisted of successive 2-minute OCPT tests in pH 7–6–5–4–2–4–5–6–7; one cycle in PBS consisted of tests in pH 5–6–7–8–7–6–5. Two cycles following a CA reset were compared to two cycles without any voltage reset. From these cycles, average drift and Nernstian sensitivity were extracted and compared.

Results, Conclusions, and Discussions:

Results:

Figure 1(a) reports a PPMM electrode in UB solution at neutral pH 7, where each CA voltage reset is indicated by an orange bar. When no reset was performed, the drift in OCP over 20 minutes was 27.2 mV. On the other hand, the OCP drift following a 0.2 V reset reduced the drift to 12.6 mV. Figure 1(b) shows OCPT cycles in UB, both with and without a 0.2 V reset. The cycles’ similarities indicate that the reset did not change the electrode’s innate sensing capabilities. Moreover, in Figure 1(c), the corresponding Nernstian sensitivities (in mV/pH) with and without reset were comparable at -73.9 and -70.8 mV/pH, respectively. Note also that the average drift among the cycles was reduced from 6.5 mV without reset to 2.8 mV with reset, demonstrating the advantages of the voltage reset.

Figure 2(a) indicates the same procedure used in UB to find the optimal voltage reset in PBS at pH 7. As shown, a 0.1 V CA reset reduced the drift most effectively, from 17 mV to 3.4 mV. When performing the OCPT cycles in Figure 2(b), conditions of no reset and 0.1 V reset were compared, and the average drift was reduced from 7.7 mV to 6.1 mV. In Figure 2(c), the Nernstian sensitivities were once again comparable at -50.9 mV/pH without reset and -56.2 mV/pH with reset.

Conclusion:

Miniature PPMM electrodes can sense precise pH changes in different types of solutions. Electrochemical readings such as open circuit potential provide consistent results. Furthermore, a voltage reset performed by a chronoamperometry test can improve the testing capabilities of these devices. This was demonstrated by the improvement of drift values across OCPT cycles while maintaining Nernstian sensitivity to pH fluctuation.

Discussions:

Further testing could be performed in different conditions such as alkaline solution or added salt concentration to assess PPMM performance. Other studied values such as hysteresis could be considered to further analyze the voltage rest condition. Overall, drift as a measure of reset and procedure efficacy supports the implementation of PPMM electrodes.

Acknowledgements (Optional): Thank you to the Department of Electrical and Computer Engineering at Southern Methodist University.