Zinc is a crucial element in biology that plays chief catalytic, structural and protein regulatory roles. Excess cytoplasmic zinc is toxic to cells so there are cell-entry and intracellular buffering mechanisms that control intracellular zinc availability. Tubulin and actin are two zinc-scavenging proteins that are essential components of the cellular cytoskeleton implicated in cell division, migration and cellular architecture maintenance. Here we demonstrate how exposure to different ZnO nanostructures, namely ZnO commercial nanoparticles and custom-made ZnO nanowires, produce acute cytotoxic effects in human keratinocytes (HaCat) and epithelial cells (HeLa) triggering a dose-dependent cell retraction and collapse. We show how engulfed ZnO nanoparticles dissolve intracellularly, triggering actin filament bundling and structural changes in microtubules, transforming these highly dynamic 25 nm diameter polymers into rigid macrotubes of tubulin, severely affecting cell proliferation and survival. Our results demonstrate that nano-ZnO causes acute cytoskeletal collapse that triggers necrosis, followed by a late reactive oxygen species (ROS)-dependent apoptotic process.
Hexagonal Si allotropes are expected to enhance light absorption in the visible range as compared to common cubic Si with diamond structure. Therefore, synthesis of these materials is crucial for the development of Si-based optoelectronics. In this work, we combine in situ high-pressure high-temperature synthesis and vacuum heating to obtain hexagonal Si. High pressure is one of the most promising routes to stabilize these allotropes. It allows one to obtain large-volume nanostructured ingots by a sequence of direct solid-solid transformations, ensuring high-purity samples for detailed characterization. Thanks to our synthesis approach, we provide the first evidence of a polycrystalline bulk sample of hexagonal Si. Exhaustive structural analysis, combining fine-powder X-ray and electron diffraction, afforded resolution of the crystal structure. We demonstrate that hexagonal Si obtained by high-pressure synthesis correspond to Si-4H polytype (ABCB stacking) in contrast with Si-2H (AB stacking) proposed previously. This result agrees with prior calculations that predicted a higher stability of the 4H form over 2H form. Further physical characterization, combining experimental data and ab initio calculations, have shown a good agreement with the established structure. Strong photoluminescence emission was observed in the visible region for which we foresee optimistic perspectives for the use of this material in Si-based photovoltaics.
Biological environments absorb and scatter light, which complicates the controlled illumination of internal thermal probes and distorts emitted light. To what extent is this a problem to measure temperature and how can it be faced?
The
incidence and mortality of cancer demand more innovative approaches
and combination therapies to increase treatment efficacy and decrease
off-target side effects. We describe a boron-rich nanoparticle composite
with potential applications in both boron neutron capture therapy
(BNCT) and photothermal therapy (PTT). Our strategy is based on gold
nanorods (AuNRs) stabilized with polyethylene glycol and functionalized
with the water-soluble complex cobalt bis(dicarbollide)
([3,3′-Co(1,2-C2B9H11)2]−), commonly known as COSAN. Radiolabeling
with the positron emitter copper-64 (64Cu) enabled in vivo tracking using positron emission tomography imaging. 64Cu-labeled multifunctionalized AuNRs proved to be radiochemically
stable and capable of being accumulated in the tumor after intravenous
administration in a mouse xenograft model of gastrointestinal cancer.
The resulting multifunctional AuNRs showed high biocompatibility and
the capacity to induce local heating under external stimulation and
trigger cell death in heterogeneous cancer spheroids as well as the
capacity to decrease cell viability under neutron irradiation in cancer
cells. These results position our nanoconjugates as suitable candidates
for combined BNCT/PTT therapies.
This work investigates the electronic
structure and photoluminescence
properties of Co2+-doped ZnO and their pressure and temperature
dependences through high-resolution absorption and emission spectroscopy
as a function of Co2+ concentration and their structural
conformations as a single crystal, thin film, nanowire, and nanoparticle.
Absorption and emission spectra of diluted ZnO:Co2+ (0.01
mol %) can be related to the 4T1(P) → 4A2(F) transition of CoO4 (T
d
), contrary to MgAl2O4:Co2+ and ZnAl2O4:Co2+ spinels
in which the red emission is ascribed to the 2E(G) → 4A2(F) transition. We show that the low-temperature
emission band consists of a 4T1(P) zero-phonon
line and a phonon-sideband, which is described in terms of the phonon
density of states within an intermediate coupling scheme (S = 1.35) involving all ZnO lattice phonons. Increasing
pressure to the sample shifts the zero-phonon line to higher energy
as expected for the 4T1(P) state upon compression.
The low-temperature emission quenches above 5 GPa as a consequence
of the pressure-induced wurtzite to rock-salt structural phase transition,
yielding a change of Co2+ coordination from 4-fold T
d
to 6-fold O
h
. We also show that the optical properties of ZnO:Co2+ (T
d
) are similar, independent of the
structural conformation of the host and the cobalt concentration.
The Co2+ enters into regular Zn2+ sites in low
concentration systems (less than 5% of Co2+), although
some slight shifts and peak broadening appear as the dimensionality
of the sample decreases. These structural effects on the optical spectra
are also supported by Raman spectroscopy.
The development of
optical nanothermometers operating in the near-infrared
(NIR) is of high relevance toward temperature measurements in biological
systems. We propose herein the use of Nd
3+
-doped lanthanum
oxychloride nanocrystals as an efficient system with intense photoluminescence
under NIR irradiation in the first biological transparency window
and emission in the second biological window with excellent emission
stability over time under 808 nm excitation, regardless of Nd
3+
concentration, which can be considered as a particular strength
of our system. Additionally, surface passivation through overgrowth
of an inert LaOCl shell around optically active LaOCl/Nd
3+
cores was found to further enhance the photoluminescence intensity
and also the lifetime of the 1066 nm,
4
F
3/2
to
4
I
11/2
transition, without affecting its (ratiometric)
sensitivity toward temperature changes. As required for biological
applications, we show that the obtained (initially hydrophobic) nanocrystals
can be readily transferred into aqueous solvents with high, long-term
stability, through either ligand exchange or encapsulation with an
amphiphilic polymer.
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