The objective of this study is to standardize protocols for clinical research into oral malodor caused by volatile sulfur compounds (VSCs). To detect VSCs, a gas chromatograph (GC) using a flame photometric detector equipped with a bandpass filter (at 393 nm) is the gold standard (sensitivity: 5 × 10(-11) gS s(-1)). The baselines of VSC concentrations in mouth air varied considerably over a week. When the subjects refrained from eating, drinking and oral hygiene including mouth rinsing, the VSC concentrations remained constant until eating. Over a 6 h period after a meal, VSC concentrations decreased dramatically (p < 0.01). These results point to optimal times and conditions for sampling subjects. Several portable devices were compared with the measurements by the GCs. Portable GCs demonstrated capabilities similar to those of the GCs. We also applied the recommended protocols described below to clinical research testing the efficacy of ZnCl(2) products, and confirmed that using the recommended protocols in a randomized crossover design would provide very clear results. Proposed protocols include: (a) a short-term study rather than a long-term study is strongly recommended, since the VSC concentrations are constant in the short term; (b) a crossover study would be the best design to avoid the effects of individual specificities on each clinical intervention; (c) measurements of VSCs should preferably be carried out using either a GC or portable GCs.

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For extremely sensitive acetone sensors, here, we introduced an alcohol-assisted surfactant-free Langmuir−Blodgett process to rapidly assemble a single-layered two-dimensional (2D) network as a suitable percolation strategy of metal oxide semiconductor nanomaterials. The single-layered 2D network formation mechanism was investigated using zinc oxide (ZnO) nanobeads (NBs). Furthermore, the correlation between the response of the gas sensor and the average percolation number of the ZnO NBs, controlled by multi-stacking the 2D network, was investigated. It was inferred that a reduction in the number of percolations led to maximization of the response. Additionally, the versatility of the optimal percolation strategy was experimentally verified by confirming similar results to that achieved with ZnO NBs when utilizing different sizes, shapes, and compositions of metal oxides. Finally, the practical effectiveness of our extremely sensitive strategy was solidified by illustrating the response enhancement in a commercial exhalation diagnostic system that measures the amount of acetone in only 1 mL of exhalation.