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Gas chromatography (GC) is a standard method to quantify volatile organic compounds (VOCs). However, this technique has high capital costs and is not suitable for real-time monitoring. Commercial metal oxide (MOX) sensors, on the other hand, are compact, cost-effective, and capable of providing real-time data to inform process control. This work used $\alpha $ -pinene in dry argon as a model system to compare the VOC detection performance of Bosch Sensortec’s BME680 sensor against the same VOC analyzed by thermal desorption-GC–mass spectrometry (TD-GC-MS) after adsorption onto a polymeric sorbent. Electronic sensor measurements were conducted in temperature- and atmosphere-controlled environments to minimize confounding effects on the resistance response. The BME680 electronic sensors showed limits of detection (LODs) ranging from 20 to 39 parts per billion (ppb), with a linear range above 40 ppb. The GC-MS in multiple reaction monitoring (MRM) mode exhibited an LOD at ( $0.61~\pm ~0.33$ ) ppb and a linear range from 1 to 100 ppb, equivalent to an adsorption volume of 2- $\mu $ L VOC gas samples at concentrations of 1–100 ppb of $\alpha $ -pinene in the gas control system. The overlapping calibration region ranges for these two methods spanned from 40 to 100 ppb. There was >30% sensor-to-sensor variability in the response from the MOX sensing components that were reduced to 5%–7% using a two-point calibration method.

We report a diazonium electro-grafting method for the covalent modification of conducting surfaces with aldehyde-reactive hydroxylamine functionalities that facilitate the wiring of redox-active (bio)molecules to electrode surfaces. Hydroxylamine near-monolayer formation is achieved via a phthalimide-protection and hydrazine-deprotection strategy that overcomes the multilayer formation that typically complicates diazonium surface modification. This surface modification strategy is characterized using electrochemistry (electrochemical impedance spectroscopy and cyclic voltammetry), X-ray photoelectron spectroscopy, and quartz crystal microbalance with dissipation monitoring. Thus-modified glassy carbon, boron-doped diamond, and gold surfaces are all shown to ligate to small molecule aldehydes, yielding surface coverages of 150–170, 40, and 100 pmol cm–2, respectively. Bioconjugation is demonstrated via the coupling of a dilute (50 μM) solution of periodate-oxidized horseradish peroxidase enzyme to a functionalized gold surface under biocompatible conditions (H2O solvent, pH 4.5, 25 °C).

Multicopper oxidases (MCO), such as laccases and bilirubin oxidases, are catalysts of wide interest in a range of biotechnological applications, especially bioremediation and energy transduction. Many of these processes take place in the presence of dissolved species, particularly halides, at concentrations high enough to inhibit the catalytic activity of MCOs. Despite this, MCO inhibition is rarely considered the focus of reviews on these enzymes. This review critically analyses the scientific literature on modes of MCO inhibition and current hypotheses on the structural origins of inhibition. The article provides a comprehensive overview of what is known from the different techniques applied to the study of MCO inhibition. These techniques include solution-based enzymatic assays, electrochemical methodologies, various spectroscopic approaches, X-ray crystallography and computational analyses. This review highlights gaps in the literature, identifies nine challenges to accurately benchmarking MCO inhibition and gives recommendations to address these challenges and to interpret published data on the subject.

This paper sets out in vitro protocols for studying the relative effectiveness of chelators used in the dissolution-based treatment of hard calcinosis. Pulverized hard calcinosis samples from human donors or synthetic hydroxyapatite nanoparticles were deposited by electrophoretic deposition on the surface of a quartz crystal microbalance sensor. Over 150 deposits of <20 μg were dissolved over the course of 1 h by aliquots of buffered, aqueous solutions of two calcium chelators, EDTA and citrate, with the surface-limited dissolution kinetics monitored with <1 s time resolution. There was no statistically significant difference in dissolution rate between the four synthetic hydroxyapatite materials in EDTA, but the dissolution rates in citrate were lower for hydroxyapatite produced by acetate or nitrate metathesis. Hard calcinosis and synthetic hydroxyapatites showed statistically identical dissolution behavior, meaning that readily available synthetic mimics can replace the rarer samples of biological origin in the development of calcinosis treatments. EDTA dissolved the hydroxyapatite deposits more than twice as fast as citrate at pH 7.4 and 37 °C, based on a first-order kinetic analysis of the initial frequency response. EDTA chelated 6.5 times more calcium than an equivalent number of moles of citrate. Negative controls using nonchelating N,N,N′,N′-tetraethylethylenediamine (TEEDA) showed no dissolution effect. Pharmaceutical dissolution testing of synthetic hydroxyapatite tablets over 6 h showed that EDTA dissolved the tablets four to nine times more quickly than citrate.