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Ex-vivo Electrochemical pH Mapping of the Gastrointestinal Tract in the Absence and Presence of Pharmacological Agents
Ex-vivo pH profiling of the upper gastrointestinal (GI) tract (of a mouse), using an electrochemical pH probe, in both the absence and presence of pharmacological agents aimed at altering acid/bicarbonate production, is reported. Three pH electrodes were first assessed for suitability using a GI tract biological mimic buffer solution containing 0.5 % mucin. These include a traditional glass pH probe, an iridium oxide (IrOx) coated electrode (both operated potentiometrically) and a quinone (Q) surface-integrated boron doped diamond (BDD-Q) electrode (voltammetric). In mucin the timescale for both IrOx and glass to obtain stable pH readings was in the ~100’s of s, most likely due to mucin adsorption, in contrast to 6 s with the BDD-Q electrode. Both the glass and IrOx pH electrodes were also compromised on robustness due to fragility and delamination (IrOx); contact with the GI tissue was an experimental requirement. BDD-Q was deemed the most appropriate. Ten measurements were made along the GI tract, esophagus (1), stomach (5) and duodenum (4). Under buffer only conditions, the BDD-Q probe tracked the pH from neutral in the esophagus, to acidic in the stomach and rising to more alkaline in the duodenum. In the presence of omeprazole, a proton pump inhibitor, the body regions of the stomach exhibited elevated pH levels. Under melatonin treatment (a bicarbonate agonist and acid inhibitor), both the body of the stomach and the duodenum showed elevated pH levels. This study demonstrates the versatility of the BDD-Q pH electrode for real-time ex-vivo biological tissue measurements.
Electric Field‐Controlled Synthesis and Characterisation of Single Metal Organic Framework Nanoparticles
Achieving control over the size distribution of metal organic framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST‐1, is achieved using a nanopipette injection method to locally mix Cu 2+ salt precursor and benzene tricarboxylate (BTC 3‐ ) ligand reagents, form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST‐1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC 3‐ . These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.
Scanning Electrochemical Cell Microscopy (SECCM) in Aprotic Solvents: Practical Considerations and Applications
Many applications in modern electrochemistry, notably electrosynthesis and energy storage/conversion take advantage of the “tunable” physicochemical properties (e.g., proton availability and/or electrochemical stability) of non-aqueous (e.g., aprotic) electrolyte media. This work develops general guidelines pertaining to the use of scanning electrochemical cell microscopy (SECCM) in aprotic solvent electrolyte media to address contemporary structure−electrochemical activity problems. Using the simple outer-sphere Fc0/+ process (Fc = ferrocene) as a model system, high boiling point (low vapor pressure) solvents give rise to highly robust and reproducible electrochemistry, whereas volatile (low boiling point) solvents need to be mixed with suitable low melting point supporting electrolytes (e.g., ionic liquids) or high boiling point solvents to avoid complications associated with salt precipitation/crystallization on the scanning (minutes to hours) timescale. When applied to perform microfabrication — specifically the electrosynthesis of the conductive polymer, polypyrrole — the optimized SECCM set up produces highly reproducible arrays of synthesized (electrodeposited) material on a commensurate scale to the employed pipet probe. Applying SECCM to map electrocatalytic activity — specifically the electro-oxidation of iodide at polycrystalline platinum — reveals unique (i.e., structure-dependent) patterns of surface activity, with grains of specific crystallographic orientation, grain boundaries and areas of high local surface misorientation identified as potential electrocatalytic “hot spots”. The work herein further cements SECCM as a premier technique for structure−function−activity studies in (electro)materials science and will open up exciting new possibilities through the use of aprotic solvents for rational analysis/design in electrosynthesis, microfabrication, electrochemical energy storage/conversion and beyond.