SCIENCE & TECHNOLOGY
from the SCENEs FROM THE ENVIRONMENTAL SCENE
STEROIDS TRANSPORTED BY DUST FROM CATTLE YARDS To beef up their herds, many cattle ranchers give their livestock steroid growth hormones. When the animals subsequently excrete steroids and their metabolites, these endocrine-disrupting compounds bind to manure and soil that gets kicked up and carried by the wind. A new study finds that this dust may be a significant source of steroids in arid regions, particularly via deposition into nearby water bodies, where
FROM THE NANO SCENE
PEPPERMINT BOMBS BLAST BACTERIAL BIOFILMS
ACS NANO
Bacterial biofilms that form around medical implants can resist attack from even the most potent antibiotics. Now, chemists have developed capsules that can smuggle a payload of antimicrobial compounds—peppermint oil and cinnamaldehyde, which gives cinnamon its flavor—into a biofilm to wipe out the stubborn bacteria (ACS Nano 2015, DOI: 10.1021/acsnano.5b01696). The researchers, led by Vincent M. Rotello
with tandem mass spectrometry, the researchers measured levels of seven steroids that cattle might excrete after receiving growth hormones. The team detected steroids on particles at all feed yards, particularly estrogen 17α-estradiol. The researchers estimate that the largest feed yard in the study, with 56,000 head of cattle, emits 63 mg of 17α-estradiol per day on airborne particles, similar to what might be transported by runoff from a feedlot of that size.
Researcher Brett R. Blackwell sets up air-sampling equipment on a cattle feed yard in West Texas.
the compounds can harm aquatic life (Environ. Sci. Technol. 2015, DOI: 10.1021/ acs.est.5b01881). Philip N. Smith, an ecotoxicologist at Texas Tech University, and colleagues collected airborne particles at five feed yards in Texas and Oklahoma over two years. Using liquid chromatography
of the University of Massachusetts, Amherst, encapsulated droplets of the oils in water using a self-assembling shell of 150-nm-diameter silica nanoparticles. Amine groups on the nanoparticles react with cinnamaldehyde, which helps to stabilize the droplets. The 7-µm-wide capsules easily penetrated biofilms, where the acidic environment broke down the silica shell, freeing the oils. The capsules killed at least 99.99% of three types of pathogenic bacteria, whereas peppermint oil alone had little impact. The researchers also showed that cinnamaldehyde in the capsules promoted the growth of fibroblast cells involved in wound healing. Rotello says the research demonstrates that common and toxicologically benign compounds could be turned into potent tools against infections simply by enhancing their delivery.
A capsule of silica nanoparticles (gray) helps droplets of peppermint oil (green) and cinnamaldehyde (red) penetrate bacterial biofilms.
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CEN.ACS.ORG
29
JULY 20, 2015
FROM THE MATERIALS SCENE
A FAST, SENSITIVE PEROVSKITE PHOTODETECTOR Engineers have built a stable perovskitebased light detector that is as sensitive as the silicon-based light sensors found in digital cameras and 1,000 times as fast as sensors made of organic semiconductors or quantum dots (ACS Photonics 2015, DOI: 10.1021/ acsphotonics.5b00164). Edward H. Sargent of the University of Toronto and colleagues built the photodetector based on a conventional solar-cell architecture, sandwiching a lead halide perovskite—which converts light to electricity with high efficiency—between layers of electrode materials. To increase the speed and sensitivity, the researchers added a 1-nm layer of aluminum oxide and a 10-nm layer of a fullerene derivative next to the perovskite. These layers block dark current—a small current that typically flows in photodetectors even when no light is hitting the device. Suppressing the dark current is crucial for increasing sensitivity, Sargent says. The device is fast, generating current in response to light in 1 microsecond, and its performance does not degrade after being illuminated for a week.
JEROD FOSTER
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