Semiconductor-enriched
single-walled carbon nanotubes (s-SWCNTs)
have potential for application as a chemiresistor for the detection
of breath compounds, including tetrahydrocannabinol (THC), the main
psychoactive compound found in the marijuana plant. Herein we show
that chemiresistor devices fabricated from s-SWCNT ink using dielectrophoresis
can be incorporated into a hand-held breathalyzer with sensitivity
toward THC generated from a bubbler containing analytical standard
in ethanol and a heated sample evaporator that releases compounds
from steel wool. The steel wool was used to capture THC from exhaled
marijuana smoke. The generation of the THC from the bubbler and heated
breath sample chamber was confirmed using ultraviolet–visible
absorption spectroscopy and mass spectrometry, respectively. Enhanced
selectivity toward THC over more volatile breath components such as
CO2, water, ethanol, methanol, and acetone was achieved
by delaying the sensor reading to allow for the desorption of these
compounds from the chemiresistor surface. Additionally, machine learning
algorithms were utilized to improve the selective detection of THC
with better accuracy at increasing quantities of THC delivered to
the chemiresistor.
Acetone is a metabolic byproduct found in the exhaled breath and can be measured to monitor the metabolic degree of ketosis. In this state, the body uses free fatty acids as its main source of fuel because there is limited access to glucose. Monitoring ketosis is important for type I diabetes patients to prevent ketoacidosis, a potentially fatal condition, and individuals adjusting to a low-carbohydrate diet. Here, we demonstrate that a chemiresistor fabricated from oxidized single-walled carbon nanotubes functionalized with titanium dioxide (SWCNT@ TiO 2 ) can be used to detect acetone in dried breath samples. Initially, due to the high cross sensitivity of the acetone sensor to water vapor, the acetone sensor was unable to detect acetone in humid gas samples. To resolve this cross-sensitivity issue, a dehumidifier was designed and fabricated to dehydrate the breath samples. Sensor response to the acetone in dried breath samples from three volunteers was shown to be linearly correlated with the two other ketone bodies, acetoacetic acid in urine and βhydroxybutyric acid in the blood. The breath sampling and analysis methodology had a calculated acetone detection limit of 1.6 ppm and capable of detecting up to at least 100 ppm of acetone, which is the dynamic range of breath acetone for someone with ketosis. Finally, the application of the sensor as a breath acetone detector was studied by incorporating the sensor into a handheld prototype breathalyzer.
Cuprate high-temperature superconducting (HTS) thin films like YBa 2 Cu 3 O 6+x (YBCO) are subject to reduction reactions with CO 2 and H 2 O. This poses a challenge for processing and storing nanoscale devices made from these films. A 1% bromine−ethanol etchant solution was investigated as a facile processing method for thin 50 nm films of patterned YBCO. Raman scattering, EDS, AFM, and HIM imaging show changes in the surface morphology and composition. RT measurements show electrical changes to a depth of ∼3 nm after bromination and a slight reduction in T c (86.5 to 86.4 K). We conclude that bromination of YBCO has minimal electrical consequences.
Findings from a recent publication in
Energy and Buildings
show that “net-zero energy” renovations can lead to net-positive energy buildings. But the results also raise concerns for the energy grid and overheating in the summer. The analysis of energy consumption of residential buildings give insight into future performance of a Dutch neighborhood’s deep energy-saving refurbishments.
In a recent work published in
Nature
Communications
, Dr. Benjamin Schäfer and colleagues demonstrate the effect of Braess’ paradox in power grids, both in a lab-scale mimic and through real-world simulations of the German power network. The results lay the groundwork for more sustainable grid development.
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