Nafion Protective Membrane Enables Using Ruthenium Oxide Electrodes for pH Measurement in Milk

Abstract

The application of conventional glass electrodes for pH measurement in food samples has a serious drawback: glass is fragile and should be handled with care in order to prevent breaking and thus contaminating the food with dangerous shattered fragments. The implementation of all-solid-state sensors allows for pH measurements without this contamination risk but their application in food samples is scarce due to their inability to be used in complex food matrices that contain fats, proteins, yeasts, etc. We can solve this problem by coating solid-state RuO2 electrodes with a semi-permeable protective NafionTM membrane layer. We show that covering screen printed potentiometric RuO2 electrodes with Nafion membrane using a drop-casting technique does not alter the performance of the electrodes in milk samples and provides similar results to the conventional glass electrode. Furthermore, we discovered that thermal treatment of Nafion-layers at 80 °C for 2 h after each layer deposition optimises the performance of the electrodes, makes them usable even in heated aqueous solutions, and increases their lifetime.

Nafion Modified Titanium Nitride pH Sensor for Future Biomedical Applications

“…The TiN + Nafion pH sensor was examined by looping pH from 2 to 12, as shown in Figure 2 a. The developed sensor shows Nernstian sensitivity (−56.6 mV/pH) and a reaction time of less than 30 s, which is consistent with previous reports of pH sensors employing this type of working electrode [ 14 , 15 ]. As seen in Figure 2 b, the pH response is linear (R 2 = 0.9999) and reproducible, as summarized in Table 2 .…”

“…The specific construction of the TiN + Nafion sensor reported here has resulted in several advantages compared to the solid-state electrodes previously reported [ 14 ]. The biggest advantage is that almost all the sputtered material is used, hence, there is no wastage, and this also allows for uniform production of bulk number of electrodes.…”

“…A TiN target (99.95% purity) with 110 W of sputter power was used to deposit TiN, utilizing radio frequency magnetron sputtering (RFMS) at room temperature. Various gas pressures in the gas chamber and argon: oxygen gas ratios were tested, as described in previous publications [ 14 , 21 ]. In Figure 1 , the TiN-sputtered layer created a vividly colored gold coating on a glass substrate [ 22 ].…”

“…Metal oxide pH electrodes were once an alternative to glass pH electrodes [ 11 , 12 , 13 , 14 ]. IrO 2 -based pH electrodes and their less popular RuO 2 -based counterparts have both been the subject of extensive research [ 12 ].…”

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

“…Manjakkal et al [ 36 ] have reported another way to eliminate redox interference by placing a thin (76 nm) Ta 2 O 5 layer on the sensitive electrode of the IrO 2 pH sensor. Pre-concentrating target analytes and minimizing interference from anionic species have both been accomplished using Nafion membranes [ 37 , 38 , 39 , 40 ]. The membrane adheres well to most electrode surfaces and can prevent fouling and surface deterioration [ 41 ].…”