81 research outputs found
Talented Mesoporous Silica Nanoparticles
The structure and functionality of
mesoporous silica nanoparticles
can be tuned by means of numerous and diverse synthetic strategies.
Focusing on experimental methods, we describe how pore size and pore
topology of the mesopore system can be modified through templating
and pore-swelling agents, as well as different synthesis conditions.
Moreover, we show how the mesoporous nanoparticles can be functionalized
through co-condensation methods with silane coupling agents, with
specific emphasis on the spatially selective anchoring of different
molecular functionalities within the nanoparticles. We discuss methods
for changing the composition of the pore walls of the mesoporous particles,
for example by including redox-sensitive sulfide bonds or by creating
autofluorescent curcumin-containing mesoporous organosilica. The efficiency
of targeted drug delivery applications strongly depends on morphological
parameters such as size and shape of the mesoporous nanoparticles.
It is demonstrated how the particle size of the mesoporous nanoparticles
can be modified over a wide range from about 30 nm to several hundred
nanometers. Developing this context further, we consider several examples
of triggered molecular mechanisms intended for the controlled intracellular
release of bioactive substances from the pore system of mesoporous
nanoparticles
Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores
The diffusion dynamics of terrylene diimide (TDI) dye
molecules
and dye-labeled double-strand DNA were studied in micrometer long
silica filaments containing collinear, oriented mesopores using single
molecule fluorescence microscopy. TDI was used as a stable and hydrophobic
probe molecule for single molecule structural analysis. We used template-free
mesoporous silica filaments with 4 nm pore diameter and chemical functionalization
with one or two types of trialkoxysilane groups to enhance the affinity
between the host system and the guest molecules. Insights about the
mesoporous structure as well as the translational and orientational
diffusion dynamics of the guest molecules observed along micrometer
long trajectories could be obtained. Additionally, the stability of
DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores
was examined, showing no degradation of the oligonucleotide upon incorporation
into the mesopores. Diffusion of both guest molecules could be controlled
by exposure to vapors of water or chloroform; the latter both induced
a reversible onâoff control of the translational movement of
the molecules
Spectrally Switchable Photodetection with Near-Infrared-Absorbing Covalent Organic Frameworks
Most covalent organic frameworks
(COFs) to date are made from relatively
small aromatic subunits, which can only absorb the high-energy part
of the visible spectrum. We have developed near-infrared-absorbing
low bandgap COFs by incorporating donorâacceptor-type isoindigo-
and thienoÂisoindigo-based building blocks. The new materials
are intensely colored solids with a high degree of long-range order
and a pseudo-quadratic pore geometry. Growing the COF as a vertically
oriented thin film allows for the construction of an ordered interdigitated
heterojunction through infiltration with a complementary semiconductor.
Applying a thienoÂisoindigo-COF:fullerene heterojunction as the
photoactive component, we realized the first COF-based UV- to NIR-responsive
photodetector. We found that the spectral response of the device is
reversibly switchable between blue- and red-sensitive, and green-
and NIR-responsive. To the best of our knowledge, this is the first
time that such nearly complete inversion of spectral sensitivity of
a photodetector has been achieved. This effect could lead to potential
applications in information technology or spectral imaging
Stabilization of the Trigonal High-Temperature Phase of Formamidinium Lead Iodide
Formamidinium lead iodide (FAPbI<sub>3</sub>) has the potential
to achieve higher performance than established perovskite solar cells
like methylammonium lead iodide (MAPbI<sub>3</sub>), while maintaining
a higher stability. The major drawback for the latter material is
that it can crystallize at room temperature in a wide bandgap hexagonal
symmetry (<i>P</i>6<sub>3</sub><i>mc</i>) instead
of the desired trigonal (<i>P</i>3<i>m</i>1) black
phase formed at a higher temperature (130 °C). Our results show
that employing a mixture of MAI and FAI in films deposited via a two-step
approach, where the MAI content is <20%, results in the exchange
of FA molecules with MA without any significant lattice shrinkage.
Additionally, we show with temperature-dependent X-ray diffraction
that the trigonal phase exhibits no phase changes in the temperature
range studied (25 to 250 °C). We attribute the stabilization
of the structure to stronger interactions between the MA cation and
the inorganic cage. Finally, we show that the inclusion of this small
amount of MA also has a positive effect on the lifetime of the photoexcited
species and results in more efficient devices
Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores
The diffusion dynamics of terrylene diimide (TDI) dye
molecules
and dye-labeled double-strand DNA were studied in micrometer long
silica filaments containing collinear, oriented mesopores using single
molecule fluorescence microscopy. TDI was used as a stable and hydrophobic
probe molecule for single molecule structural analysis. We used template-free
mesoporous silica filaments with 4 nm pore diameter and chemical functionalization
with one or two types of trialkoxysilane groups to enhance the affinity
between the host system and the guest molecules. Insights about the
mesoporous structure as well as the translational and orientational
diffusion dynamics of the guest molecules observed along micrometer
long trajectories could be obtained. Additionally, the stability of
DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores
was examined, showing no degradation of the oligonucleotide upon incorporation
into the mesopores. Diffusion of both guest molecules could be controlled
by exposure to vapors of water or chloroform; the latter both induced
a reversible onâoff control of the translational movement of
the molecules
Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores
The diffusion dynamics of terrylene diimide (TDI) dye
molecules
and dye-labeled double-strand DNA were studied in micrometer long
silica filaments containing collinear, oriented mesopores using single
molecule fluorescence microscopy. TDI was used as a stable and hydrophobic
probe molecule for single molecule structural analysis. We used template-free
mesoporous silica filaments with 4 nm pore diameter and chemical functionalization
with one or two types of trialkoxysilane groups to enhance the affinity
between the host system and the guest molecules. Insights about the
mesoporous structure as well as the translational and orientational
diffusion dynamics of the guest molecules observed along micrometer
long trajectories could be obtained. Additionally, the stability of
DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores
was examined, showing no degradation of the oligonucleotide upon incorporation
into the mesopores. Diffusion of both guest molecules could be controlled
by exposure to vapors of water or chloroform; the latter both induced
a reversible onâoff control of the translational movement of
the molecules
Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores
The diffusion dynamics of terrylene diimide (TDI) dye
molecules
and dye-labeled double-strand DNA were studied in micrometer long
silica filaments containing collinear, oriented mesopores using single
molecule fluorescence microscopy. TDI was used as a stable and hydrophobic
probe molecule for single molecule structural analysis. We used template-free
mesoporous silica filaments with 4 nm pore diameter and chemical functionalization
with one or two types of trialkoxysilane groups to enhance the affinity
between the host system and the guest molecules. Insights about the
mesoporous structure as well as the translational and orientational
diffusion dynamics of the guest molecules observed along micrometer
long trajectories could be obtained. Additionally, the stability of
DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores
was examined, showing no degradation of the oligonucleotide upon incorporation
into the mesopores. Diffusion of both guest molecules could be controlled
by exposure to vapors of water or chloroform; the latter both induced
a reversible onâoff control of the translational movement of
the molecules
Direct Visualization of Dye and Oligonucleotide Diffusion in Silica Filaments with Collinear Mesopores
The diffusion dynamics of terrylene diimide (TDI) dye
molecules
and dye-labeled double-strand DNA were studied in micrometer long
silica filaments containing collinear, oriented mesopores using single
molecule fluorescence microscopy. TDI was used as a stable and hydrophobic
probe molecule for single molecule structural analysis. We used template-free
mesoporous silica filaments with 4 nm pore diameter and chemical functionalization
with one or two types of trialkoxysilane groups to enhance the affinity
between the host system and the guest molecules. Insights about the
mesoporous structure as well as the translational and orientational
diffusion dynamics of the guest molecules observed along micrometer
long trajectories could be obtained. Additionally, the stability of
DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores
was examined, showing no degradation of the oligonucleotide upon incorporation
into the mesopores. Diffusion of both guest molecules could be controlled
by exposure to vapors of water or chloroform; the latter both induced
a reversible onâoff control of the translational movement of
the molecules
Guided in Situ Polymerization of MEH-PPV in Mesoporous Titania Photoanodes
Incorporation
of conjugated polymers into porous metal oxide networks is a challenging
task, which is being pursued via many different approaches. We have
developed the guided in situ polymerization of polyÂ(2-methoxy-5-(2â˛-ethylhexyloxy)-<i>p</i>-phenylenevinylene) (MEH-PPV) in porous titania films by
means of surface functionalization. The controlled polymerization
via the Gilch route was induced by an alkoxide base and by increasing
the temperature. The selected and specially designed surface-functionalizing
linker molecules mimic the monomer or its activated form, respectively.
In this way, we drastically enhanced the amount of MEH-PPV incorporated
into the porous titania phase compared to nonfunctionalized samples
by a factor of 6. Additionally, photovoltaic measurements were performed.
The devices show shunting or series resistance limitations, depending
on the surface functionalization prior to in situ polymerization of
MEH-PPV. We suggest that the reason for this behavior can be found
in the orientation of the grown polymer chains with respect to the
titania surface. Therefore, the geometry of the anchoring via the
linker molecules is relevant for exploiting the full electronic potential
of the conjugated polymer in the resulting hybrid composite. This
observation will help to design future synthesis methods for new hybrid
materials from conjugated polymers and n-type semiconductors to take
full advantage of favorable electronic interactions between the two
phases
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A novel synthesis method for large-pore, well-aligned 2D hexagonal mesoporous silica thin films is reported. The alignment was achieved by confinement in poly(dimethylsiloxane) (PDMS) microgrooves without the necessity of additional forces (such as electric fields). We describe the influence of various experimental conditions including the way the grooves are filled, surface modification at the solid/liquid interfaces, and the height-to-width ratio of the microgrooves on mesopore alignment. With this technique, highly oriented mesoporous silica channels can be obtained at a length scale of several millimeters. For a nondestructive, detailed, and wide-ranging structural and dynamic characterization of the as-synthesized mesochannel silica network, dye molecules were incorporated into the channels at concentrations suitable for single-molecule microscopy. A âmaximum projectionâ of individual frames recorded with a fluorescence microscope immediately gives a global overview (âmapâ) of the pore structure, thus providing direct feedback for tuning synthesis conditions. In addition, deeper insights into the real nanoscale structure of the mesoporous silica framework were obtained through high-accuracy single-molecule tracking experiments. The high spatial accuracy of the experiments allowed for the direct observation of jumps of single dye molecules between individual channels in the mesoporous silica host. Nevertheless, due to the low concentration of defects, the diffusion could be described as a 1D random walk where the molecules diffuse along the highly oriented, parallel channels and sometimes switch from channel to channel through small defects in the pore walls. Furthermore, it could be shown with single-molecule microscopy that template removal and calcination of the aligned films results in an increased defect concentration; however, the overall order of the structures remained intact
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