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

Abstract

In this study, a solid-state modified pH sensor with RF magnetron sputtering technology was developed. The sensor consists of an active electrode consisting of a titanium nitride (TiN) film with a protective membrane of Nafion and a reference glass electrode of Ag/AgCl. The sensitivity of the pH sensor was investigated. Results show a sensor with excellent characteristics: sensitivity of 58.6 mV/pH for pH values from 2 to 12, very short response time of approximately 12 s in neutral pH solutions, and stability of less than 0.9 mV in 10 min duration. Further improvement in the performance of the TiN sensor was studied by application of a Nafion protective membrane. Nafion improves the sensor sensitivity close to Nernstian by maintaining a linear response. This paves the way to implement TiN with Nafion protection to block any interference species during real time applications in biosensing and medical diagnostic pH sensors.

Keywords: Nafion; medical applications; outer membrane; pH sensing; redox effects; titanium nitride.

Figure 1

Chemical structure of Nafion [18].

Figure 2

Schematic representation of 85 nm thick TiN electrode with Nafion layer (left) and an image of the actual Nafion modified electrode (right).

Figure 3

Schematic showing deposition of Nafion membrane on 85 nm TiN electrode using spin coating.

Figure 4

SEM secondary electron images taken with Hitachi SU3500 of (a–d) 85 nm TiN sensor modified with Nafion film at various magnifications, and (e) unmodified 85nm TiN sensor [45].

Figure 4

SEM secondary electron images taken with Hitachi SU3500 of (a–d) 85 nm TiN sensor modified with Nafion film at various magnifications, and (e) unmodified 85nm TiN sensor [45].

Figure 5

Thickness optimization of Nafion on 85 nm TiN film by assessing the sensitivity as a key performance indicator.

Figure 6

Graphical representation of potential difference vs. time for pH 2, 4 and 7.