6 research outputs found
Tuning Molecular-Level Polymer Conformations Enables Dynamic Control over Both the Interfacial Behaviors of Ag Nanocubes and Their Assembled Metacrystals
In surface chemistry-directed
nanoparticle self-assembly, it remains
challenging to continuously modulate nanoparticle behavior at the
oil/water interface without replacing surface functionality or particle
morphology. Here, we utilize solvent-tunable molecular-level polymer
conformation changes to achieve “multiple metacrystals using
one nanoparticle with one chemical functionality”. We use Ag
nanocubes functionalized with a mixed monolayer of thiol-terminated
poly(ethylene glycol) (PEG) and hexadecanethiol
(C16). We continuously modulate PEG conformation from swollen to coiled
states by decreasing solvent polarity, whereas C16 promotes nanocube
dispersion in organic carrier solvents. Such PEG conformation changes
drive Ag nanocubes to adopt tilted, standing, and planar configurations
at the oil/water interface, with their interfacial positions changing
from halfway across the interface to almost immersed within the oil
phase. We also identify four specific polarities which enable Ag nanocubes
to assemble into large-area metacrystals with linear, hexagonal, and
square close-packed lattices. Our work establishes an innovative strategy
to achieve robust tunability of nanoparticle interfacial behavior
and unprecedented modulation of metacrystal structure
Transformative Two-Dimensional Array Configurations by Geometrical Shape-Shifting Protein Microstructures
Two-dimensional (2D) geometrical shape-shifting is prevalent in nature, but remains challenging in man-made “smart” materials, which are typically limited to single-direction responses. Here, we fabricate geometrical shape-shifting bovine serum albumin (BSA) microstructures to achieve circle-to-polygon and polygon-to-circle geometrical transformations. In addition, transformative two-dimensional microstructure arrays are demonstrated by the ensemble of these responsive microstructures to confer structure-to-function properties. The design strategy of our geometrical shape-shifting microstructures focuses on embedding precisely positioned rigid skeletal frames within responsive BSA matrices to direct their anisotropic swelling under pH stimulus. This is achieved using layer-by-layer two photon lithography, which is a direct laser writing technique capable of rendering spatial resolution in the sub-micrometer length scale. By controlling the shape, orientation and number of the embedded skeletal frames, we have demonstrated well-defined arc-to-corner and corner-to-arc transformations, which are essential for dynamic circle-to-polygon and polygon-to-circle shape-shifting, respectively. We further fabricate our shape-shifting microstructures in periodic arrays to experimentally demonstrate the first transformative 2D patterned arrays. Such versatile array configuration transformations give rise to structure-to-physical properties, including array porosity and pore shape, which are crucial for the development of on-demand multifunctional “smart” materials, especially in the field of photonics and microfluidics
Transformative Two-Dimensional Array Configurations by Geometrical Shape-Shifting Protein Microstructures
Two-dimensional (2D) geometrical shape-shifting is prevalent in nature, but remains challenging in man-made “smart” materials, which are typically limited to single-direction responses. Here, we fabricate geometrical shape-shifting bovine serum albumin (BSA) microstructures to achieve circle-to-polygon and polygon-to-circle geometrical transformations. In addition, transformative two-dimensional microstructure arrays are demonstrated by the ensemble of these responsive microstructures to confer structure-to-function properties. The design strategy of our geometrical shape-shifting microstructures focuses on embedding precisely positioned rigid skeletal frames within responsive BSA matrices to direct their anisotropic swelling under pH stimulus. This is achieved using layer-by-layer two photon lithography, which is a direct laser writing technique capable of rendering spatial resolution in the sub-micrometer length scale. By controlling the shape, orientation and number of the embedded skeletal frames, we have demonstrated well-defined arc-to-corner and corner-to-arc transformations, which are essential for dynamic circle-to-polygon and polygon-to-circle shape-shifting, respectively. We further fabricate our shape-shifting microstructures in periodic arrays to experimentally demonstrate the first transformative 2D patterned arrays. Such versatile array configuration transformations give rise to structure-to-physical properties, including array porosity and pore shape, which are crucial for the development of on-demand multifunctional “smart” materials, especially in the field of photonics and microfluidics
Formulating an Ideal Protein Photoresist for Fabricating Dynamic Microstructures with High Aspect Ratios and Uniform Responsiveness
The physical properties
of aqueous-based stimuli-responsive photoresists
are crucial in fabricating microstructures with high structural integrity
and uniform responsiveness during two-photon lithography. Here, we
quantitatively investigate how various components within bovine serum
albumin (BSA) photoresists affect our ability to achieve BSA microstructures
with consistent stimuli-responsive properties over areas exceeding
10<sup>4</sup> μm<sup>2</sup>. We unveil a relationship between
BSA concentration and dynamic viscosity, establishing a threshold
viscosity to achieve robust BSA microstructures. We also demonstrate
the addition of an inert polymer to the photoresist as viscosity enhancer.
A set of systematically optimized processing parameters is derived
for the construction of dynamic BSA microstructures. The optimized
BSA photoresists and processing parameters enable us to extend the
two-dimensional (2D) microstructures to three-dimensional (3D) ones,
culminating in arrays of micropillars with aspect ratio > 10. Our
findings foster the development of liquid stimuli-responsive photoresists
to build multifunctional complex 3D geometries for applications such
as bioimplantable devices or adaptive photonic systems
Redox-Responsive Hyperbranched Poly(amido amine)s with Tertiary Amino Cores for Gene Delivery
Redox-responsive hyperbranched poly(amido
amine)s (PAAs) with tertiary
amino cores and amine, poly(ethylene glycol) (PEG) and hydroxyl terminal
groups were prepared for DNA delivery respectively. The DNA condensation
capability of PAAs was investigated using gel electrophoresis, and
the results showed that PAA terminated with 1-(2-aminoethyl)piperazine
(AEPZ) (BAA) is the most efficient in binding plasmid DNA (pDNA).
The diameter and zeta-potential of polyplexes from PAAs were characterized
using dynamic light scattering (DLS), and the morphology of the polyplexes
was obtained using atomic force microscopy (AFM). All the PAAs were
able to condense pDNA into nanoparticles with diameters between 50
and 200 nm with a positive surface charge when the weight ratio of
polymer/DNA was higher than 20. Glutathione (GSH)-induced DNA release
from polyplexes and the buffering capability of PAAs were investigated
as well. Cytotoxicity of PAAs and <i>in vitro</i> gene transfection
of polyplexes were evaluated in HEK293, COS-7, MCF-7 and Hep G2 cell
lines, respectively. The results reflect that PAAs show remarkably
low or even no cytotoxicity, and that PAA with amino terminal groups
mediates the most efficient gene transfection with the transfection
efficiency comparable to that of 25 kDa polyethylenimine. Further
the effects of the presence of buthionine sulfoximine (BSO) on the
transfection efficiency and cytotoxicity of BAA polyplexes were investigated
Direct Metal Writing and Precise Positioning of Gold Nanoparticles within Microfluidic Channels for SERS Sensing of Gaseous Analytes
We
demonstrate a one-step precise direct metal writing of well-defined
and densely packed gold nanoparticle (AuNP) patterns with tunable
physical and optical properties. We achieve this by using two-photon
lithography on a Au precursor comprising poly(vinylpyrrolidone) (PVP)
and ethylene glycol (EG), where EG promotes higher reduction rates
of Au(III) salt via polyol reduction. Hence, clusters of monodisperse
AuNP are generated along raster scanning of the laser, forming high-particle-density,
well-defined structures. By varying the PVP concentration, we tune
the AuNP size from 27.3 to 65.0 nm and the density from 172 to 965
particles/μm<sup>2</sup>, corresponding to a surface roughness
of 12.9 to 67.1 nm, which is important for surface-based applications
such as surface-enhanced Raman scattering (SERS). We find that the
microstructures exhibit an SERS enhancement factor of >10<sup>5</sup> and demonstrate remote writing of well-defined Au microstructures
within a microfluidic channel for the SERS detection of gaseous molecules.
We showcase in situ SERS monitoring of gaseous 4-methylbenzenethiol
and real-time detection of multiple small gaseous species with no
specific affinity to Au. This one-step, laser-induced fabrication
of AuNP microstructures ignites a plethora of possibilities to position
desired patterns directly onto or within most surfaces for the future
creation of multifunctional lab-on-a-chip devices