Sniffing out water pollution
Taking a cue from canine noses, a research
team led by Guodong Liang of Sun Yat-sen
University and Ben Zhong Tang of Hong Kong
University of Science and Technology created
fluorescent nanosheets that build themselves
to sniff out organic pollutants in water.
The team starts with basket-shaped molecules of hydrophilic carbohydrates, called cyclodextrins, and attaches
fluorescent tetraphenylethene groups. When added to an aqueous
solution, these structures self-assemble into nanoscopic, sandwich-like sheets about 4 nanometers thick. Two layers of cyclodextrin act
as the bread slices surrounding a filling of tetraphenylethene.
Although the exterior of the circular cyclodextrin molecules is
hydrophilic, they have hydrophobic interior cavities. These cavities
collect and funnel volatile organic molecules into the tetraphenylethene layer. Once in that layer, the contaminants dim the fluorescing
compounds. The design of the self-assembled sheets is modeled after
dog noses, which use bony structures to funnel scent molecules for
The fluorescent nanosheets are extremely sensitive to aromatic
xylenes, with a limit of detection at 5 µg/L, the team says. Smaller
organic pollutants are also detectable. The sensitivity appears to correlate with how well the organic compound fits into the sensor’s cyclodextrin cavities.
Read more about the research: “Bioinspired Fluorescent Nanosheets for Rapid
and Sensitive Detection of Organic Pollutants in Water,” ACS Sensors, 2016,
Glow technique warns of
invisible cracks in plastics
Microscopic cracks in a material can spread and grow
into larger fissures — ones that can split apart the
plastics and composites used in airplanes, spacecraft,
electronics, and pipes. A simple new technique can
reveal tiny, invisible cracks in a wide variety of plastics
by making the cracks glow.
An early-warning strategy could allow engineers to replace or repair
critical components and prevent catastrophes. Nancy R. Sottos, Jeffrey S.
Moore, and colleagues at the University of Illinois at Urbana-Champaign
embedded various polymers with polyurethane microcapsules filled
with a dilute solution of 1, 1, 2,2-tetraphenylethylene (TPE), which fluo-
resces brightly when TPE molecules aggregate. Formation of tiny cracks
in the plastic ruptures the capsules, leading to solvent evaporation
and growth of TPE crystals on the capsule shell. Ultraviolet (UV) light
causes the crystals to shine bright blue. The most promising results
were obtained from plastics loaded with 10% microcapsules by weight.
Scratches made in these plastics blended in under visible light but
glowed when illuminated with a UV lamp. The researchers could detect
cracks smaller than 2 µm up to 40 days after the damage occurred.
Read more about the research: “A Robust Damage-Reporting Strategy for
Polymeric Materials Enabled by Aggregation-Induced Emission,” ACS Central
Science, 2016, 2 ( 9), pp 598–603.
Fans of stevia will
be interested to hear
that Manus Biosynthesis
has announced a new process to
make commercial quantities of the natural zero-calorie
sweetener rebaudioside M (Reb M) for the first time.
Most commercial stevia products are based on stevioside and
rebaudioside A, which are the most abundant sweeteners in the stevia
plant. Like some artificial sweeteners, these compounds have a subtle
unfavorable, bitter, metallic off-taste that becomes more pronounced
at higher concentrations. But Reb M is a stevia compound thought
to have a better overall taste profile. At less than 0.01% of total leaf
weight, it is difficult to source economically. Building on core technology developed by the Massachusetts Institute of Technology’s Gregory
Stephanopoulos and co-workers, Manus Biosynthesis has used an
engineered bacterium and a new fermentation process to produce
bulk amounts of Reb M in better than 95% purity.
Read more about the research: “Microbial Production of Steviol Glycosides,”
WIPO Patent WO/2016/073740A1.
COMPILED BY BLAKE ARONSON
Source: Chemical & Engineering News, cen.acs.org
The nanosheet sensors are coated in cyclodextrins, which guide organic pollut-
ants into the device. The pollutants can then switch off fluorescent tetraphenyl-