3 research outputs found
Ultrafast Exciton Dynamics in Silicon Nanowires
Ultrafast exciton dynamics in one-dimensional (1D) silicon
nanowires
(SiNWs) have been investigated using femtosecond transient absorption
techniques. A strong transient bleach feature was observed from 500
to 770 nm following excitation at 470 nm. The bleach recovery was
dominated by an extremely fast feature that can be fit to a triple
exponential with time constants of 0.3, 5.4, and âŒ75 ps, which
are independent of probe wavelength. The amplitude and lifetime of
the fast component were excitation intensity-dependent, with the amplitude
increasing more than linearly and the lifetime decreasing with increasing
excitation intensity. The fast decay is attributed to excitonâexciton
annihilation upon trap state saturation. The threshold for observing
this nonlinear process is sensitive to the porosity and surface properties
of the sample. To help gain insight into the relaxation pathways,
a four-state kinetic model was developed to explain the main features
of the experimental dynamics data. The model suggests that after initial
photoexcitation, conduction band (CB) electrons become trapped in
the shallow trap (ST) states within 0.5 ps and are further trapped
into deep trap (DT) states within 4 ps. The DT electrons finally recombine
with the hole with a time constant of âŒ500 ps, confirming the
photophysical processes to which we assigned the decays
Ordered Ag/Si Nanowires Array: Wide-Range Surface-Enhanced Raman Spectroscopy for Reproducible Biomolecule Detection
Surface-enhanced
Raman scattering (SERS) systems utilizing the
interparticle nanogaps as hot spots have demonstrated ultrasensitive
single-molecule detection with excellent selectivity yet the electric
fields are too confined in the small nanogaps to enable reproducible
biomolecule detections. Here, guided by finite-difference-time-domain
simulation, we report hexagonal-packed silver-coated silicon nanowire
(Ag/SiNW) arrays as a nanogap-free SERS system with wide-range electric
fields and controlled interwire separation. Significantly, the system
achieves a SERS detection of long double-strand DNA of 25â50
nm in length with a relative standard deviation (RSD) of 14% for measurements
of above 4000 spots over an area of 200 Ă 200 ÎŒm<sup>2</sup>. The high reproducibility in the SERS detection is attributed to
(1) the large interwire spacing of 150 nm that allows access and excitation
of large biomolecules; and (2) 600 nm wide-range electric field generated
by propagating surface plasmons along the surface of continuous Ag
coating on a SiNW. Moreover, a reproducible multiplex SERS measurement
is also demonstrated with RSDs of 7â16% with an enhancement
factor of âŒ10<sup>6</sup>. The above results show that the
ordered Ag/SiNW array system may serve as an excellent SERS platform
for practical chemical and biological detection
Tea Polyphenol Epigallocatechin Gallate Protects Against Nonalcoholic Fatty Liver Disease and Associated Endotoxemia in Rats via Modulating Gut Microbiota Dysbiosis and Alleviating Intestinal Barrier Dysfunction and Related Inflammation
Nonalcoholic
fatty liver disease (NAFLD) is characterized
by fat
accumulation and inflammation. Epigallocatechin gallate (EGCG) has
been proven to be effective against NAFLD, but its hepatoprotective
mechanisms based on the âgut microbiota-barrier-liver axisâ
are still not fully understood. Herein, the results demonstrated that
EGCG effectively ameliorated NAFLD phenotypes and metabolic disorders
in rats fed a high-fat diet (HFD), and inhibited intestinal barrier
dysfunction and inflammation, which is also supported in the experiment
of Caco-2 cells. Moreover, EGCG could restore gut microbiota diversity
and composition, particularly promoting beneficial microbes, including
short-chain fatty acids (SCFAs) producers, such as Lactobacillus, and suppressing Gram-negative bacteria,
such as Desulfovibrio. The microbial
modulation raised SCFA levels, decreased lipopolysaccharide levels,
inhibited the TLR4/NF-ÎșB pathway, and strengthened intestinal
barrier function via Nrf2 pathway activation, thereby alleviating
liver steatosis and inflammation. Spearmanâs correlation analysis
showed that 24 key OTUs, negatively or positively associated with
NAFLD and metabolic disorders, were also reshaped by EGCG. Our results
suggested that a combinative improvement of EGCG on gut microbiota
dysbiosis, intestinal barrier dysfunction, and inflammation might
be a potential therapeutic target for NAFLD