Search for: All records

Harnessing the potential of exhaled breath analysis is an emerging frontier in medical diagnostics, given breath is a rich source of volatile organic compound (VOC) biomarkers for different medical conditions. A current downfall in this field, however, is the lack of standardized and widely available methods for offline sampling of exhaled VOCs. Herein, strides are taken toward the standardization of breath sampling in Tedlar bags by exploring several factors that can impact VOC heterogeneity, including tubing material, chemical composition of collection bags, breath fractionation, exhalation volume, and transfer flow rate. After bag-based sampling standardization, performance was benchmarked using two offline breath sampling methods, Tedlar bags and the Respiration Collector for In Vitro Analysis (ReCIVA). Three volunteers from the laboratory with no known respiratory diseases donated ≥ n = 5 samples collected onto adsorption tubes via each method, which were analyzed through thermal desorption (TD) coupled with gas chromatography-mass spectrometry (GC–MS). Data processing revealed a set of 15 highly reliable on-breath VOCs detected across volunteers, and most analytes (except indole) demonstrated higher sensitivity using Tedlar bags. Calculating relative standard deviation (RSD) values showed Tedlar bags were also significantly more reproducible compared to the ReCIVA (p < 0.03). Agreement between the two methods was demonstrated through correlating VOC signals with high statistical significance (R2 = 0.70), indicating both devices are well situated for biomarker discovery applications. 

Volatile organic compounds (VOCs) in urine headspace are potential biomarkers for different medical conditions, as canines can detect human diseases simply by smelling VOCs. Because dogs can detect disease-specific VOCs, gas chromatography–mass spectrometry (GC–MS) systems may be able to differentiate medical conditions with enhanced accuracy and precision, given they have unprecedented efficiency in separating, quantifying, and identifying VOCs in urine. Advancements in instrumentation have permitted the development of portable GC–MS systems that analyze VOCs at the point of care, but these are designed for environmental monitoring, emergency response, and manufacturing/processing. The purpose of this study is to repurpose the HAPSITE® ER portable GC–MS for identifying urinary VOC biomarkers. Method development focused on optimizing sample preparation, off-column conditions, and instrumental parameters that may affect performance. Once standardized, the method was used to analyze a urine standard (n = 10) to characterize intra-day reproducibility. To characterize inter-day performance, n = 3 samples each from three volunteers (and the standard) were analyzed each day for a total of four days (n = 48 samples). Results showed the method could detect VOC signals with adequate reproducibility and distinguish VOC profiles from different volunteers with 100% accuracy. 

One step pore diffusion mechanism of lithium ion transport in the solid electrolyte interphase (SEI) layer with discrete inorganic components enables the fast lithium conduction without slow solid state diffusion process. 

TEMPO has been widely explored as one of the most promising catholyte redox scaffolds in aqueous redox flow batteries, but the often-observed performance degradation raises concern with respect to its chemical instability. In this work, we demonstrate that the charged TEMPO species (i.e., TEMPO+) lack sufficient stability and also determine the major decomposition pathways. The decay products of TEMPO+ are experimentally analyzed using combined tools including nuclear magnetic resonance and mass spectroscopy. Reductive conversion to 2,2,6,6-tetramethylpiperidine (TEMPH) is commonly observed for a variety of 4-O-substituted TEMPO derivatives. The general detection of alkene and related carbonyl signals, in conjunction with the electrolyte acidification, reveals a deprotonation-initiated ring opening route that proceeds towards TEMPO decay. The protons on the β carbon are susceptible to chemical extraction by nucleophilic agents such as hydroxyl and the formed piperidine. This finding highlights the intrinsic structural factors for TEMPO degradation and will shed light on the potential stabilization strategies to afford long-cycling TEMPO-based flow batteries. 

The inexpensive sulfur raw material is promising to enable cost-effective redox flow batteries for long duration energy storage. But the catastrophic through-membrane crossover of polysulfides remains a severe challenge resulting in irreversible performance degradation and short cycle life. In this work, we demonstrate that use of a permselective cation exchange membrane yields a two orders of magnitude enhancement in polysulfide retention compared to the benchmark Nafion membrane. Combined physico-chemical, spectroscopic, and microscopic analyses suggest more disordered sidechain structures, which lead to the more hydrophobic nature and smaller hydrophilic domains in the membrane. The microstructural features contribute to the effective mitigation of polysulfide crossover. As a result, the cycle life of polysulfide/ferricyanide flow cells is boosted over a substantially extended test time. This finding sheds light on the fundamental membrane factors that cause polysulfide permeation and can provide feasible directions in the development of permselective membranes for polysulfide flow batteries. 

Previous studies have shown that volatile organic compounds (VOCs) are potential biomarkers of breast cancer. An unanswered question is how urinary VOCs change over time as tumors progress. To explore this, BALB/c mice were injected with 4T1.2 triple negative murine tumor cells in the tibia. This typically causes tumor progression and osteolysis in 1–2 weeks. Samples were collected prior to tumor injection and from days 2–19. Samples were analyzed by headspace solid phase microextraction coupled to gas chromatography–mass spectrometry. Univariate analysis identified VOCs that were biomarkers for breast cancer; some of these varied significantly over time and others did not. Principal component analysis was used to distinguish Cancer (all Weeks) from Control and Cancer Week 1 from Cancer Week 3 with over 90% accuracy. Forward feature selection and linear discriminant analysis identified a unique panel that could identify tumor presence with 94% accuracy and distinguish progression (Cancer Week 1 from Cancer Week 3) with 97% accuracy. Principal component regression analysis also demonstrated that a VOC panel could predict number of days since tumor injection (R2 = 0.71 and adjusted R2 = 0.63). VOC biomarkers identified by these analyses were associated with metabolic pathways relevant to breast cancer.