Long-term stability of screen-printed pseudo-reference electrodes for electrochemical biosensors

Abstract

Pseudo reference electrodes forms an essential part of electrochemical transducers, where they are used to maintain a reference potential for the system. Yet, little is known about their long-term stability, and any drift may cause undesired changes in the sensor signal. This paper investigates the stability of the reference potential of five material systems of screen-printed reference electrodes. Their potential was continuously monitored for a duration of 40 days in a phosphate buffered solution, and any signal changes were corroborated with EDX elemental analyses, SEM micrographs and cyclic voltammetry. The electrodes were considered to be stable as long as they remained within 30 mV of their initial potential throughout the study. It was found that Ag/AgCl electrodes with a 3:1 atomic ratio kept a stable reference potential (±2.2 mV), whereas Ag/AgCl electrodes with a 9:1 atomic ratio, despite showing good overall constancy of ±3.2 mV, seemed to statistically lose stability towards the end of the 40 day trial due to AgCl depletion through dissolution. The daily potential drift for the respective Ag/AgCl electrodes were −0.2 mV (3:1 ratio) and −0.1 mV (9:1 ratio), suggesting a proportionality between the amount of dissociated AgCl close to the electrode surface and the initial AgCl loading. Electrodes consisting of only Ag showed tendencies towards a mixed potential contribution, which reduced the long-term stability (±24.2 mV) as well as the longevity span (2 days). Ag/Pd electrodes proved to be more unstable (±29.7 mV), with an average lifetime of around 3.5 days. Pt had the greatest potential instability (±59.8 mV), rendering its average lifetime to less than a day. It was shown that electrodes which deviates from the Ag/AgCl equilibrium had the greatest potential variation with time.

Development of New Simple Compositions of Silver Inks for the Preparation of Pseudo-Reference Electrodes

“…The stability of the potential of the pseudo-reference electrodes was evaluated in the interval of 1 h by the OCP technique. This methodology was similar to those demonstrated in the articles by Dawkins et al and by Søpstad et al [ 7 , 12 ]. A two-electrode system was used as follows: Ag|AgCl|KCl(sat.)…”

“…It is known that despite this lack of equilibrium, the potential of the pseudo-reference electrode can be surprisingly constant during experiments, being an interesting aspect to be explored in the development of simple and disposable devices [ 10 , 11 ]. In the literature, some proposals for making reference electrodes can be found using silver, such as those developed by Dawkins et al and by Søpstad et al [ 7 , 12 ]. Also, we can highlight devices using commercial silver inks, such as those developed by Lan et al and Moya et al [ 8 , 13 ], who studied the design of reference electrodes using paper as a substrate and inkjet printing, respectively.…”

“…Although there are some methodologies involving the use of systems with only carbon as a reference electrode, it is noted that this substrate without silver ink coating has low potential stability so that considerable variations can occur along the time [ 20 , 25 , 26 , 27 ]. Thus, the development of conductive silver inks for building more stable pseudo-reference electrodes is a fantastic approach to enabling large-scale production at reduced cost [ 7 , 12 ]. In this context, the present work reports the development of two Ag conductive inks through the dispersion of Ag powder in shellac and nail polish.…”

Novel Flexible Ag/AgCl Quasi-Reference Electrode with Fishbone Nanowire Structure for Remarkable Potential Stability, Long-Term Reliability, and Noninvasive Electrocardiography

“…It was apparent that the fishbone Ag was chlorinated into nanoparticles, while the nanoparticles were still arranged in fishbone-like structures. The fragmented clusters in the fishbone-like structures might have been caused by the massive formation of AgCl due to the harsh chemical chlorination reaction. ,, Figure b shows the OCP results of the Fishbone-Ag/AgCl qRE prepared by EC (red line) and the NP-Ag/AgCl qRE prepared by CC (black line) in 3 mol L –1 KCl solution. The OCP signal of the Fishbone-Ag/AgCl qRE was extremely stable, whereas the OCP potential of the NP-Ag/AgCl qRE showed apparent fluctuation.…”

Paper-Based Screen-Printed Electrodes: A New Generation of Low-Cost Electroanalytical Platforms

“…Moreover, since paper-based devices are often conceived for single-use measurements, the required operational stability of the RE is limited to one unique measurement and not to a large number, as in the case of conventional REs. However, where uninterrupted gathering of sensor data over longer periods of time is required, as in the case of inaccessible or remote locations where sensor replacement is difficult, potential stability has to be thoroughly studied [ 30 ].…”