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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 (HPLC) 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.

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 both 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 100–500 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.

This article describes the electrochemical reduction of bromate ions in strongly alkaline media on platinum electrodes. Bromates’ importance stems from its wide use in a variety of industrial processes, its incorporation into energy storage devices, as well as its known toxicity, which has led to it being designated as a human carcinogen. Interestingly, during the electro-reduction of bromate in alkaline solutions sustained oscillatory behavior was observed in both current and potential under both potentiostatic and galvanostatic control. Mechanistic characterization using electrochemical impedance spectroscopy (EIS) lead to the discovery that the oscillatory behavior is driven by the presence of a negative differential resistance (NDR). The EIS measurements allowed for the classification of the bromate oscillator into the HN-NDR class, which was supported by potentiostatic oscillations emerging once sufficient external resistance was included into the system as well as oscillating under galvanostatic conditions. Through a systematic exploration of experimental conditions, the electrochemical bromate oscillator also displayed complexity in the form of mixed-mode oscillations as well as complex bursting patterns.

We report an accessible fabrication procedure to prepare customizable pyrolyzed photoresin electrodes (PPE) for electroanalytical applications. A stereolithography 3D printer was used to pattern carbon containing photoresin on a quartz substrate before being pyrolyzed to yield a carbon electrode with X and Y dimensions ranging from mm to a minimum feature size of approximately 200 µm as determined by optical microscopy. Stylus profilometery was used to determine PPEs have an approximate step height of 600 nm. Atomic force microscopy was employed to examine the surface roughness of PPEs, which were found to have a rms roughness of approximately 25 nm. Cyclic voltammetry with hexaammineruthenium chloride was performed to examine the electrochemical behavior of the PPEs, which was consistent with the Randles-Sevcik equation and commercial glassy carbon electrodes. Hydrodynamic voltammetry in a microfluidic device was also demonstrated.