Voltammetric pH Measurements in Unadulterated Foodstuffs, Urine, and Serum with 3D-Printed Graphene/Poly(Lactic Acid) Electrodes

Abstract

The pH of a system is a critical descriptor of its chemistry -impacting reaction rates, solubility, chemical speciation, and homeostasis. As a result, pH is one of the most commonly measured parameters in food safety, clinical, and environmental laboratories. Glass pH probes are the gold standard for pH measurements, but suffer drawbacks including frequent recalibration, wet storage of the glass membrane, difficulty in miniaturization, and interferences from alkali metals. In this work, we describe a voltammetric pH sensor that uses a 3D-printed graphene/poly(lactic acid) filament electrode that is pretreated to introduce quinone functional groups to the graphene surface. After thoroughly characterizing the pretreatment parameters using outer-sphere and inner-sphere redox couples, we measured pH by reducing the surface-bound quinones, which undergo a pH-dependent 2e -/2H + reduction. The position of the redox peak was found to shift -60 ± 2 mV pH -1 at 25 ºC, which is in excellent agreement with the theoretical value predicted by the Nernst Equation (-59.2 mV pH -1 ). Importantly, the sensors did not require the removal of dissolved oxygen prior to successful pH measurements. We investigated the impact of common interfering species (Pb 2+ and Cu 2+ ) and found that there was no impact on the measured pH. We subsequently challenged the sensors to measure the pH of unadulterated complex samples including cola, vinegar, serum, and urine, and obtained excellent agreement compared to a glass pH electrode. In addition to the positive analytical characteristics, the sensors are extremely cheap and easy to fabricate, making them highly accessible to a wide range of researchers. These results pave the way for customizable pH sensors that can be fabricated in (nearly) any geometry for targeted applications using 3D-printing. File list (2)download file view on ChemRxiv ph sensors_ms_submitted.pdf (576.07 KiB) download file view on ChemRxiv ph sensors_esi_submitted.pdf (322.36 KiB)

3D Printed Reactionware for Synthetic Electrochemistry with Hydrogen Fluoride Reagents

“…3D printing, or additive manufacturing, is a rapidly maturing technology that has progressed from an engineering curiosity to become a viable, cost-effective manufacturing or prototyping technique with applications in several fields of research, [42][43][44][45][46][47] including chemical synthesis, [48][49][50][51][52][53][54][55][56] analytics, [57][58][59][60][61] and, albeit to a lesser extent, synthetic electrochemistry. [49,[62][63][64][65][66][67] As the object is built up layer by layer in a computer-controlled process, high resolution objects can be rapidly manufactured without the operator having to be familiar with the range of machining instruments and techniques normally employed.…”

Novel Self-Calibrating Amperometric and Ratiometric Electrochemical Nanotip Microsensor for pH Measurement in Rat Brain

“…The above variations are close to the previously reported values. 29,42,43 Additionally, the proposed sensors were successfully and directly used in rat whole blood, which did not require dilution prior to analysis, but negligible pH change upon global cerebral ischemia for 60 min by the present developed sensor (Figure S25, Supporting Information). Further work on changing intracellular dynamic pH changes is in progress in our lab.…”

“…The past decades have witnessed progressive developments in pH monitoring technologies, such as nuclear magnetic resonance, − fluorescence, − surface-enhanced Raman scattering, , and electrochemical methods. − At present, the most common method for measuring pH is the electrochemical assay based on conventional microelectrodes with high spatial resolution, simplicity, and high sensitivity. However, most pH detections were performed using potentiometric sensors, and only a few of them were used to measure the pH e of cells, and even fewer were used to in vivo measure the pH e of mammalian cells. − Recently, a different approach for pH measurement involves the use of voltammetric techniques.…”

“…However, most pH detections were performed using potentiometric sensors, and only a few of them were used to measure the pH e of cells, and even fewer were used to in vivo measure the pH e of mammalian cells. − Recently, a different approach for pH measurement involves the use of voltammetric techniques. There are two ways to introduce pH sensitivity to voltammetric pH probes: chemically modifying an electrode surface with a pH-responsive chemical species or using intrinsic functional groups on the surfaces of carbon electrodes. − In this case, a pH-dependent mediator is selected, and its electrochemical activity is monitored (reduction or oxidation). A popular choice is quinone moieties, which have been previously utilized in the literature. − For example, the pioneering work of Wightman’s group, which depended on fast-scan cyclic voltammetry, opened a great way for characterizing the local pH changes in brains .…”

3D Printed Bioelectronic Microwells

“…When the filament is inserted into the 3D printer, it is heated to a semi‐molten state and extruded on a platform and through its solidification, the programmed sensor is formed. [ 15–19 ] This digital fabrication process offers multiple advantages, such as desktop‐sized apparatus, design flexibility, and transferability though e‐mail (“e‐mailed” sensors), fast prototyping, effortlessness of operation by non‐trained handlers, while it produces negligible non‐toxic waste. In addition, FDM enables the single‐step fabrication of multimaterial sensors using filaments with different properties (e.g., conductive and non‐conductive) via multiple extruder 3D printers.…”