4 research outputs found
Large Centimeter-Sized Macroporous Ferritin Gels as Versatile Nanoreactors
Organized
assemblies of bionanoparticles such as ferritin provides
templates that can be exploited for nanotechnological applications.
Organization of ferritin into well-defined three-dimensional assemblies
is challenging and has attracted considerable attention recently.
We have synthesized, for the first time, large (centimeter-sized)
self-standing macroporous scaffold monoliths from ferritin bionanoparticles,
using dynamic templating of surfactant H<sub>1</sub> domains. These
scaffolds comprise three-dimensionally connected strands of ferritin,
organized as a porous gel with porosity ∼55 μm. The iron
oxide inside the ferritin scaffold can be easily replaced with catalytically
active monodisperse zerovalent transition metal nanoparticles using
a very simple protocol. Since the ferritin is cross-linked in the
scaffold, it is significantly robust with enhanced thermal stability
and better tolerance toward several organic solvents in comparison
to the native ferritin bionanoparticle. In addition, the scaffold
macropores facilitate substrate and reagent transport and hence the
monoliths containing active Pd or iron oxide nanoparticles inside
apo-ferritin bionanoparticles were used as a recyclable heterogeneous
catalyst for the oxidation of 2,3,6-trimethyl phenol to 2,3,6-trimethyl-1,4-benzoquinone
(precursor for Vitamin E synthesis) and for Suzuki–Miyaura
cross-coupling reaction in both aqueous and organic solvents. The
protein shell around the nanoparticles protects them from agglomeration,
a phenomenon that otherwise plagues nanoparticles-based catalysis.
The presence of macropores allow the ferritin scaffold to act as catalytic
monolith for continuous flow reactions having rapid reaction rates,
while offering a low pressure drop. Finally, the Pd@apo-ferritin scaffold
was immobilized inside a steel cartridge and used for the continuous
flow hydrogenation of alkenes to their corresponding alkanes for 15
cycles without any loss of activity
Recombinant Spider Silk Hydrogels for Sustained Release of Biologicals
Therapeutic
biologics (i.e., proteins) have been widely recognized
for the treatment, prevention, and cure of a variety of human diseases
and syndromes. However, design of novel protein-delivery systems to
achieve a nontoxic, constant, and efficient delivery with minimal
doses of therapeutic biologics is still challenging. Here, recombinant
spider silk-based materials are employed as a delivery system for
the administration of therapeutic biologicals. Hydrogels made of the
recombinant spider silk protein eADF4Â(C16) were used to encapsulate
the model biologicals BSA, HRP, and LYS by direct loading or through
diffusion, and their release was studied. Release of model biologicals
from eADF4Â(C16) hydrogels is in part dependent on the electrostatic
interaction between the biological and the recombinant spider silk
protein variant used. In addition, tailoring the pore sizes of eADF4Â(C16)
hydrogels strongly influenced the release kinetics. In a second approach,
a particles-in-hydrogel system was used, showing a prolonged release
in comparison with that of plain hydrogels (from days to week). The
particle-enforced spider silk hydrogels are injectable and can be
3D printed. These initial studies indicate the potential of recombinant
spider silk proteins to design novel injectable hydrogels that are
suitable for delivering therapeutic biologics
Fe-TAML Encapsulated Inside Mesoporous Silica Nanoparticles as Peroxidase Mimic: Femtomolar Protein Detection
Peroxidase, such as horseradish peroxidase
(HRP), conjugated to antibodies are routinely used for the detection
of proteins via an ELISA type assay in which a critical step is the
catalytic signal amplification by the enzyme to generate a detectable
signal. Synthesis of functional mimics of peroxidase enzyme that display
catalytic activity which far exceeds the native enzyme is extremely
important for the precise and accurate determination of very low quantities
of proteins (fM and lower) that is necessary for early clinical diagnosis.
Despite great advancements, analyzing proteins of very low abundance
colorimetrically, a method that is most sought after since it requires
no equipment for the analysis, still faces great challenges. Most
reported HRP mimics that show catalytic activity greater than native
enzyme (∼10-fold) are based on metal/metal-oxide nanoparticles
such as Fe<sub>3</sub>O<sub>4</sub>. In this paper, we describe a
second generation hybrid material developed by us in which approximately
25 000 alkyne tagged biuret modified Fe-tetraamido macrocyclic
ligand (Fe-TAML), a very powerful small molecule synthetic HRP mimic,
was covalently attached inside a 40 nm mesoporous silica nanoparticle
(MSN). Biuret-modified Fe-TAMLs represent one of the best small molecule
functional mimics of the enzyme HRP with reaction rates in water close
to the native enzyme and operational stability (pH, ionic strength)
far exceeding the natural enzyme. The catalytic activity of this hybrid
material is around 1000-fold higher than that of natural HRP and 100-fold
higher than that of most metal/metal oxide nanoparticle based HRP
mimics reported to date. We also show that using antibody conjugates
of this hybrid material it is possible to detect and, most importantly,
quantify femtomolar quantities of proteins colorimetrically in an
ELISA type assay. This represents at least 10-fold higher sensitivity
than other colorimetric protein assays that have been reported using
metal/metal oxide nanoparticles as HRP mimic. Using a human IgG expressing
cell line, we were able to demonstrate that the protein of interest
human IgG could be detected from a mixture of interfering proteins
in our assay
Soft Colloidal Scaffolds Capable of Elastic Recovery after Large Compressive Strains
Assemblies of inorganic or glassy
particles are typically brittle
and cannot sustain even moderate deformations. This restricts the
use of such materials to applications where they do not experience
significant loading or deformation. Here, we demonstrate a general
strategy to create centimeter-size macroporous monoliths, composed
primarily (>90 wt %) of colloidal particles, that recover elastically
after compression to about one-tenth their original size. We employ
ice templating of an aqueous dispersion of particles, polymer, and
cross-linker such that cross-linking happens in the frozen state.
This method yields elastic composite scaffolds for starting materials
ranging from nanoparticles to micron-sized dispersions of inorganics
or glassy lattices. The mechanical response of the monoliths is also
qualitatively independent of polymer type, molecular weight, and even
cross-linking chemistry. Our results suggest that the monolith mechanical
properties arise from the formation of a unique hybrid microstructure,
generated by cross-linking the polymer during ice templating. Particles
that comprise the scaffold walls are connected by a cross-linked polymeric
mesh. This microstructure results in soft monoliths, with moduli ∼O
(10<sup>4</sup> Pa), despite the very high particle content in their
walls. A remarkable consequence of this microstructure is that the
monolith mechanical response is entropic in origin: the modulus of
these scaffolds increases with temperature over a range of 140 K.
We show that interparticle connections formed by cross-linking during
ice templating determine the monolith modulus and also allow relative
motion between connected particles, resulting in entropic elasticity