Nafion Modified Titanium Nitride pH Sensor for Future Biomedical Applications

Abstract

pH sensors are increasingly being utilized in the biomedical field and have been implicated in health applications that aim to improve the monitoring and treatment of patients. In this work, a previously developed Titanium Nitride (TiN) solid-state pH sensor is further enhanced, with the potential to be used for pH regulation inside the human body and for other biomedical, industrial, and environmental applications. One of the main limitations of existing solid-state pH sensors is their reduced performance in high redox mediums. The potential shift E0 value of the previously developed TiN pH electrode in the presence of oxidizing or reducing agents is 30 mV. To minimize this redox shift, a Nafion-modified TiN electrode was developed, tested, and evaluated in various mediums. The Nafion-modified electrode has been shown to shift the E0 value by only 2 mV, providing increased accuracy in highly redox samples while maintaining acceptable reaction times. Overcoming the redox interference for pH measurement enables several advantages of the Nafion-modified TiN electrode over the standard pH glass electrode, implicating its use in medical diagnosis, real-time health monitoring, and further development of miniaturized smart sensors.

Fabrication and Optimization of Nafion as a Protective Membrane for TiN-Based pH Sensors

“…An increase in hysteresis, a decrease in sensitivity, and a linear response were observed for TiN + N3 electrodes. As with previously fabricated unaltered TiN electrodes [ 43 ], the sensitivity of Nafion-covered electrodes was comparable to and nearly equal to the theoretical value (58.8 mV/pH). With more Nafion layers present, there was also a minor drop in sensitivity; however, except for TiN + N3, it remained rather close to the Nernstain sensitivity.…”

“…Active TiN pH electrodes were made using RF magnetron spray producing 85 nm of TiN layer on the underlying 2 inch × 2 inch 0.5 mm thick alumina substrate. As previously reported [ 43 ], the parameters of the sputtered-deposition process used for the manufacture of small metal nitride films under controlled conditions to produce the most effective solid pH sensor are Ti target of 99.95% purity with a power of 350 W sputter at 10:2 Ar: N 2 at 2 mTorr pressure at room temperature. The TiN film electrode was then further refined with Nafion layer, by incorporating a 5 µL spin of 5% Nafion (Sigma) solution onto the active electrode, which was then fired at 210 °C for one hour under a vacuum of <10 mTorr using rapid thermal annealing (RTA).…”

“…The sensitivity, E 0 , hysteresis, and drift of the sensors were then determined using these results. While electrode drift was determined using the slope of the line-of-best-fit for the data at pH 12 across the measurement period, hysteresis was calculated using the difference between successive measurements at pH 12 [ 43 ]. The amount of time needed to bring an electrode within 3 mV (or 0.05 pH) of the stable potential was called the electrode reaction time [ 44 ].…”

“…Membrane deposition and treatment parameters, such as deposition process and annealing/boiling temperature, affect the proton conductivity of Nafion. The Nafion membrane was deposited on the electrode surface by drop-casting a commercially available solution and sensing mechanism of the developed layers was reported previously [ 43 ]. However, methods presented in various research papers varied in the quantity of Nafion layers and in the method of drying the Nafion.…”

Steganography in IoT: Information Hiding with Joystick and Touch Sensors

“…Input devices collect data from the environment. They may measure temperature [ 46 ], medical parameters [ 47 ], displacement [ 48 ], pH [ 49 ], pressure [ 50 ], humidity [ 51 ], inertia [ 52 ], etc. Output devices broadcast messages to the external world.…”