No abstract

This technical note describes a method for fabricating ion-selective membranes (ISMs) for use in potentiometric sensing by using 3D printing technology. Here, we demonstrate the versatility of this approach by fabricating ISMs and investigating their performance in both liquid-contact and solid-contact ion-selective electrode (ISE) configurations. Using 3D printed ISMs resulted in highly stable (drift of ∼17 μV/h) and highly reproducible (<1 mV deviation) measurements. Furthermore, we show the seamless translation of these membranes into reliable, carbon fiberand paper-based potentiometric sensors for applications at the point-of-care. To highlight the modifiability of this approach, we fabricated sensors for bilirubin, an important biomarker of liver health; benzalkonium, a common preservative used in the pharmaceutical industry; and potassium, an important blood electrolyte. The ability to mass produce sensors using 3D printing is an attractive advantage over conventional methods, while also decreasing the time and cost associated with sensor fabrication.

Benzalkonium (BA+) chloride is one of the most common preservatives used in prescription-based and over-the-counter eye drops. Knowing the concentration of BA+ in eye drops is important for quality control (at the pharmaceutical preparation stage) and human health (ocular toxicity has been linked to BA+ use). This paper describes the design and fabrication of a benzalkonium-selective potentiometric sensor for the determination of BA+ in ophthalmic solutions. The sensor is composed of a 3D-printed ion-selective membrane (ISM) that selectively measures BA+ in the presence of potentially interfering ions routinely found in ophthalmic formulations (i.e., Mg2+, Ca2+, Na+, and K+). The 3D printed BA+-ion-selective electrodes (ISEs) produced a Nernstian response of 55 mV/Decade across a range of 1.0 mM to 31.0 µM BA+ along with an LOD of 8 µM, which covers the relevant concentration range found in ophthalmic solutions. The 3D printed BA+-ISEs proved to be highly stable with an average drift of 205 µV/hr. Successful measurement of BA+ in diluted ophthalmic solutions was completed from 100 to 500 µM. The mass production capability afforded by 3D-printing offers a unique and intriguing fabrication protocol for developing low-cost sensors which could be incorporated quickly and seamlessly by pharmaceutical companies or community-based pharmacies.

Chloroquine is an important, and commonly prescribed, antimalarial drug which can lead to the development of retinopathy and potential blindness. This paper reports on the design and fabrication of a highly selective potentiometric sensor for chloroquine, demonstrating the first use of ionophore-doped ion-selective electrodes (ISEs) for its detection. Several molecules with known affinity for chloroquine were investigated as potential ionophores for the chloroquine ISE. Incorporating melanin as the ionophore resulted in a linear detection range of 10 mM to 2.4 µM and a limit of detection of 630 nM. Importantly, the melanin-doped ISE resulted in an increased selectivity by several orders of magnitude compared to an ionophore-free ISE. This added selectivity allowed for detection of chloroquine without interference from other commonly prescribed antimalarials, hydroxychloroquine, and quinine that have similar molecular structures. To determine the applicability of the melanin-doped ISE, chloroquine was successfully measured in human urine samples, and the results of the sensor were validated using a high-performance liquid chromatography protocol. To demonstrate the utility of the sensor, the components of the ISE were translated to a paper-based potentiometric device capable of detecting chloroquine between 10 mM and 100 µM, covering the biologically relevant range excreted in human urine

No abstract