Regular ArticleFabrication of newspaper-based potentiometric platforms for flexible and disposable ion sensors
Graphical abstract
Flexible and disposable USB-type ion sensors were fabricated using newspaper-based platforms by coating of parylene C and patterning of metal layers, showing a near-Nernstian reponse, a wide detection range, a rapid response time, repeatability, selectivity, and stability.
Introduction
The detection and monitoring of electrolyte ions are of considerable importance in many fields of industry, agriculture, biology, and environmental [1], [2], [3]. Potentiometric sensors based on ion-selective electrode (ISE) materials are widely used because they readily and rapidly provide reliable measurements [4], [5], [6], [7], [8], [9], [10], [11], [12]. Potentiometric ion sensors typically have a two-electrode configuration comprising an ion-sensing electrode and a reference electrode, and the potentials between these two electrodes can be quantitatively determined using the Nernst equation. However, increasing demands for healthcare monitoring, point-of-care testing, and on-site environmental detection systems require the development of flexible, lightweight, low cost, easy-to-fabricate, and disposable sensor devices [12], [13], [14], [15], [16], [17]. Hence, in addition to sensing electrode materials, flexible substrates, such as, flexible thermoplastic polymers, textiles, and paper, have attracted much attention [18], [19], [20], [21], [22]. Over recent years, researchers have devised various flexible devices based on paper-based platforms for use in sensors, strain gauges, and in microfluidic and energy storage devices [23], [24], [25], [26], [27], [28]. Paper is attractive for sensor applications because it is readily available, biodegradable, inexpensive, and mechanically and chemically stable. Some paper-based sensors have been developed, but important obstacles remain, which include the retention of chemical and mechanical stabilities when paper is wetted.
Herein, we demonstrate that newspaper-based platforms are useful for the fabrication of flexible and disposable potentiometric ion sensors for the detection of electrolyte cations, such as, H+ and K+. The technique developed involved the chemical vapor deposition (CVD) of parylene C onto newspaper with uniform coating. The resulting parylene C-coated newspaper (PC-paper) could provide low-cost, disposable, and mechanically and chemically stable electrochemical platforms for the development of potentiometric ion sensors. To demonstrate the feasibility of such platforms, PC-paper-based pH and K+ sensors were fabricated using a two-electrode configuration. The pH and K+ sensors produced showed near ideal Nernstian sensitivity, good repeatability, good ion selectivity, and low potential drift.
Section snippets
Reagents and materials
Aniline (99.5%), potassium hydrogen phthalate, potassium phosphate monobasic, borax, tris(hydroxymethyl)aminomethane, sodium hydroxide, hydrochloric acid, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ammonium chloride, valinomycin (potassium ionophore I), potassium tetrakis(4-chlorophenyl)borate (KTClPB), bis(2-ethylhexyl) sebacate (DOS), poly(vinyl chloride) (PVC) with high molecular weight, and tetrahydrofuran (THF) were purchased from Sigma Aldrich. Sulfuric
Results and discussion
Fig. 1a shows scheme of the CVD-based parylene C coating process, which reproducibly produces a continuous thin layer of parylene C on newspaper. Optical and SEM images of pristine newspaper and PC-paper confirmed the presence of a uniform, thin, transparent parylene C coating (Fig. 1b). SEM images showed the rough networks of cellulose fibers and pores in pristine paper became smoother after parylene C coating due to the formation of polymer layers. In addition, PC-paper exhibited water
Conclusions
We developed a disposable, low-cost, and flexible paper-based ion-sensing platforms for potentiometric ion sensors. Direct coating of parylene C on newspaper efficiently increased Young’s modulus and tensile stress and maintained mechanical properties even after wetting and exhibited chemical resistance to strong acid and base solutions. Stencil lithography enabled the production of user-friendly USB-type sensing platforms. To demonstrate the potential of the PC-paper sensing platforms for ion
Acknowledgements
This research was supported by the Bio & Medical Technology Development Program of the National Research Foundation (NRF) & funded by the Korean government (MSIP) (No. 2015M3A9D7067457) and Cooperative Research Program for Agriculture Science & Technology Development (Project No. PJ01252602) from the Rural Development Administration (RDA) of the Republic of Korea. This research was supported in part by the BioNano HealthGuard Research Center, funded by the Ministry of Science, ICT &Future
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These authors contributed to the paper equally.