A Disposable Planar Paper‐Based Potentiometric Ion‐Sensing Platform

Abstract

Ion-selective electrodes (ISEs) are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding ap otentiometric cell into paper, complete with an ISE, areference electrode,and apaper-based microfluidic sample zone that offer the full function of ac onventional ISE setup.T he disposable planar paper-based ion-sensing platform is suitable for low-cost point-of-care and in-field testing applications.T he design is symmetrical and each interfacial potential within the cell is well defined and reproducible,s ot hat the response of the device can be theoretically predicted. Forademonstration of clinical applications,p aper-based Cl À and K + sensors are fabricated with highly reproducible and linear responses towards different concentrations of analyte ions in aqueous and biological samples.The single-use devices can be fabricated by ascalable method, do not need any pretreatment prior to use,a nd only require asample volume of 20 mL.Ion sensing is an important topic in various fields,s uch as clinical and environmental analysis.[1] As often introduced in general chemistry courses,s elective and quantitative ion sensing can be achieved with ap otentiometric cell that comprises an ion-selective electrode (ISE), ar eference electrode,and avoltmeter as areadout tool. It has been estimated that each year over ab illion measurements with ISEs are performed globally in clinical laboratories alone.[1a] Besides detection of analytes with low (for example,K + ,Na)and high valence charges (such as heparin), [2] biosensing of proteins [3] and detection of electrically neutral species have been achieved with ISEs. [4] With the growing demand for point-of-care and in-field testing,p aper has recently attracted much attention as as imple,a ffordable,f lexible,a nd scalable substrate for microfluidic assays.[5] Although paper-based colorimetric sensors offer the advantage of simple data interpretation, detection with electrochemical techniques is insensitive to color interferences and is generally more quantitative. [6] Existing paper-based ion sensors rely on various techniques, including potentiometry, [7] coulometry, [8] chronopotentiometry, [9] and colorimetry. [10] Paper was used in these devices either as am icrofluidic sampling tool or as as ubstrate to mechanically support the sensing components.S trip-type ISEs known as Ektachem slides were available in the 1980s, [11] and were recently adapted with ap aper substrate to support carbon nanotubes or conducting polymers as solid contacts.[7b,c] Although miniaturizable,t hese devices need cumbersome electrode conditioning and individual calibration. A more integrated device,reported by Whitesides et al.,utilizes ar eusable ISE membrane placed between two disposable wax-imprinted paper substrates.[7d] With different ISE membranes,v arious clinically relevant ions can be detected. However,t he ISE membranes have to be well conditioned, and the devices have to be carefully assembled and calibrated, which may impede their practical ...

Recent advances in potentiometric biosensors

“…Bearing in mind trends in micro-fabrication and nanotechnology, miniaturized ISEs, especially solid-contact microelectrodes, have become a unique tool to investigate in life sciences and environmental monitoring. Also, microfluidic-based analytical devices (mPADs) have emerged as an attractive analytical and detection platform for the development of simple and cost-effective molecular diagnostic assays [90,149]. The integration of mPADs with potentiometric ISEs enables the development of flexible, portable, and inexpensive biosensing devices.…”

A Paper-Based Potentiometric Platform for Determination of Water Hardness

“…Paper-based potentiometry lowers costs and makes the construction of chemical sensors more accessible while preserving the analytical performance. Several examples of paper-based potentiometry for decentralized applications have been described during recent years [20][21][22][23][24]. Our group has demonstrated that paper-based sensors for peroxide and biosensors for glucose in whole blood can be successfully developed.…”

Potentiometric Sensors with Polymeric Sensing and Reference Membranes Fully Integrated into a Sample‐Wicking Polyester Textile

“…To date, there are only a few examples of fully‐integrated paper‐based ISEs, i. e., devices that require no assembly and take advantage of wicking of the sample into paper to hold the sample. They include paper‐based reference electrodes with a Ag/AgCl/KCl half cell [20] as well as devices with ion‐selective and ionic‐liquid reference membranes embedded into paper, with colloid‐imprinted mesoporous carbon as solid contact [21–23] . Fully‐integrated devices have also been produced with automated ink‐jet printing [24] …”