10 research outputs found
Thermally Tunable Ultrasensitive Infrared Absorption Spectroscopy Platforms Based on Thin Phase-Change Films
The
thermal tunability of the optical and electrical properties
of phase-change materials has enabled the decades-old rewritable optical
data storage and the recently commercialized phase-change memory devices.
Recently, phase-change materials, in particular, Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST), have been considered for other thermally
configurable photonics applications, such as active plasmonic surfaces.
Here, we focus on nonplasmonic field enhancement and demonstrate the
use of the phase-change materials in ultrasensitive infrared absorption
spectroscopy platforms employing interference-based uniform field
enhancement. The studied structures consist of patternless thin GST
and metal films, enabling simple and large-area fabrication on rigid
and flexible substrates. Crystallization of the as-fabricated amorphous
GST layer by annealing tunes (redshifts) the field-enhancement wavelength
range. The surfaces are tested with ultrathin chemical and biological
probe materials. The measured absorption signals are found to be comparable
or superior to the values reported for the ultrasensitive infrared
absorption spectroscopy platforms based on plasmonic field-enhancement
Universal Infrared Absorption Spectroscopy Using Uniform Electromagnetic Enhancement
Infrared absorption spectroscopy
has greatly benefited from the electromagnetic field enhancement offered
by plasmonic surfaces. However, because of the localized nature of
plasmonic fields, such field enhancements are limited to nanometer-scale
volumes. Here, we demonstrate that a relatively small, but spatially
uniform field enhancement can yield a superior infrared detection
performance compared to the plasmonic field enhancement exhibited
by optimized infrared nanoantennas. A specifically designed CaF<sub>2</sub>/Al thin film surface is shown to enable observation of stronger
vibrational signals from the probe material, with wider bandwidth
and a deeper spatial extent of the field enhancement as compared to
such plasmonic surfaces. It is demonstrated that the surface structure
presented here can enable chemically specific and label-free detection
of organic monolayers using surface-enhanced infrared spectroscopy,
indicating a great potential in highly sensitive yet cost-effective
biomolecular sensing applications
Counting Molecules with a Mobile Phone Camera Using Plasmonic Enhancement
Plasmonic
field enhancement enables the acquisition of Raman spectra at a single
molecule level. Here we investigate the detection of surface enhanced
Raman signal using the unmodified image sensor of a smart phone, integrated
onto a confocal Raman system. The sensitivity of a contemporary smart
phone camera is compared to a photomultiplier and a cooled charge-coupled
device. The camera displays a remarkably high sensitivity, enabling
the observation of the weak unenhanced Raman scattering signal from
a silicon surface, as well as from liquids, such as ethanol. Using
high performance wide area plasmonic substrates that enhance the Raman
signal 10<sup>6</sup> to 10<sup>7</sup> times, blink events typically
associated with single molecule motion, are observed on the smart
phone camera. Raman spectra can also be collected on the smart phone
by converting the camera into a low resolution spectrometer with the
inclusion of a collimator and a dispersive optical element in front
of the camera. In this way, spectral content of the blink events can
be observed on the plasmonic substrate, in real time, at 30 frames
per second
Counting Molecules with a Mobile Phone Camera Using Plasmonic Enhancement
Plasmonic
field enhancement enables the acquisition of Raman spectra at a single
molecule level. Here we investigate the detection of surface enhanced
Raman signal using the unmodified image sensor of a smart phone, integrated
onto a confocal Raman system. The sensitivity of a contemporary smart
phone camera is compared to a photomultiplier and a cooled charge-coupled
device. The camera displays a remarkably high sensitivity, enabling
the observation of the weak unenhanced Raman scattering signal from
a silicon surface, as well as from liquids, such as ethanol. Using
high performance wide area plasmonic substrates that enhance the Raman
signal 10<sup>6</sup> to 10<sup>7</sup> times, blink events typically
associated with single molecule motion, are observed on the smart
phone camera. Raman spectra can also be collected on the smart phone
by converting the camera into a low resolution spectrometer with the
inclusion of a collimator and a dispersive optical element in front
of the camera. In this way, spectral content of the blink events can
be observed on the plasmonic substrate, in real time, at 30 frames
per second
Counting Molecules with a Mobile Phone Camera Using Plasmonic Enhancement
Plasmonic
field enhancement enables the acquisition of Raman spectra at a single
molecule level. Here we investigate the detection of surface enhanced
Raman signal using the unmodified image sensor of a smart phone, integrated
onto a confocal Raman system. The sensitivity of a contemporary smart
phone camera is compared to a photomultiplier and a cooled charge-coupled
device. The camera displays a remarkably high sensitivity, enabling
the observation of the weak unenhanced Raman scattering signal from
a silicon surface, as well as from liquids, such as ethanol. Using
high performance wide area plasmonic substrates that enhance the Raman
signal 10<sup>6</sup> to 10<sup>7</sup> times, blink events typically
associated with single molecule motion, are observed on the smart
phone camera. Raman spectra can also be collected on the smart phone
by converting the camera into a low resolution spectrometer with the
inclusion of a collimator and a dispersive optical element in front
of the camera. In this way, spectral content of the blink events can
be observed on the plasmonic substrate, in real time, at 30 frames
per second
Counting Molecules with a Mobile Phone Camera Using Plasmonic Enhancement
Plasmonic
field enhancement enables the acquisition of Raman spectra at a single
molecule level. Here we investigate the detection of surface enhanced
Raman signal using the unmodified image sensor of a smart phone, integrated
onto a confocal Raman system. The sensitivity of a contemporary smart
phone camera is compared to a photomultiplier and a cooled charge-coupled
device. The camera displays a remarkably high sensitivity, enabling
the observation of the weak unenhanced Raman scattering signal from
a silicon surface, as well as from liquids, such as ethanol. Using
high performance wide area plasmonic substrates that enhance the Raman
signal 10<sup>6</sup> to 10<sup>7</sup> times, blink events typically
associated with single molecule motion, are observed on the smart
phone camera. Raman spectra can also be collected on the smart phone
by converting the camera into a low resolution spectrometer with the
inclusion of a collimator and a dispersive optical element in front
of the camera. In this way, spectral content of the blink events can
be observed on the plasmonic substrate, in real time, at 30 frames
per second
Exploiting Native Al<sub>2</sub>O<sub>3</sub> for Multispectral Aluminum Plasmonics
Aluminum,
despite its abundance and low cost, is usually avoided
for plasmonic applications due to losses in visible/infrared regimes
and its interband absorption at 800 nm. Yet, it is compatible with
silicon CMOS processes, making it a promising alternative for integrated
plasmonic applications. It is also well known that a thin layer of
native Al<sub>2</sub>O<sub>3</sub> is formed on aluminum when exposed
to air, which must be taken into account properly while designing
plasmonic structures. Here, for the first time we report exploitation
of the native Al<sub>2</sub>O<sub>3</sub> layer for fabrication of
periodic metal–insulator–metal (MIM) plasmonic structures
that exhibit resonances spanning a wide spectral range, from the near-ultraviolet
to mid-infrared region of the spectrum. Through fabrication of silver
nanoislands on aluminum surfaces and MIM plasmonic surfaces with a
thin native Al<sub>2</sub>O<sub>3</sub> layer, hierarchical plasmonic
structures are formed and used in surface-enhanced infrared spectroscopy
(SEIRA) and surface-enhanced Raman spectrocopy (SERS) for detection
of self-assembled monolayers of dodecanethiol
Multivalent Presentation of Cationic Peptides on Supramolecular Nanofibers for Antimicrobial Activity
Noncovalent and electrostatic interactions
facilitate the formation
of complex networks through molecular self-assembly in biomolecules
such as proteins and glycosaminoglycans. Self-assembling peptide amphiphiles
(PA) are a group of molecules that can form nanofibrous structures
and may contain bioactive epitopes to interact specifically with target
molecules. Here, we report the presentation of cationic peptide sequences
on supramolecular nanofibers formed by self-assembling peptide amphiphiles
for cooperative enhanced antibacterial activity. Antibacterial properties
of self-assembled peptide nanofibers were significantly higher than
soluble peptide molecules with identical amino acid sequences, suggesting
that the tandem presentation of bioactive epitopes is important for
designing new materials for bactericidal activity. In addition, bacteria
were observed to accumulate more rapidly on peptide nanofibers compared
to soluble peptides, which may further enhance antibacterial activity
by increasing the number of peptide molecules interacting with the
bacterial membrane. The cationic peptide amphiphile nanofibers were
observed to attach to bacterial membranes and disrupt their integrity.
These results demonstrate that short cationic peptides show a significant
improvement in antibacterial activity when presented in the nanofiber
form
Fabrication of Supramolecular n/p-Nanowires <i>via</i> Coassembly of Oppositely Charged Peptide-Chromophore Systems in Aqueous Media
Fabrication
of supramolecular electroactive materials at the nanoscale
with well-defined size, shape, composition, and organization in aqueous
medium is a current challenge. Herein we report construction of supramolecular
charge-transfer complex one-dimensional (1D) nanowires consisting
of highly ordered mixed-stack π-electron donor–acceptor
(D–A) domains. We synthesized n-type and p-type β-sheet
forming short peptide-chromophore conjugates, which assemble separately
into well-ordered nanofibers in aqueous media. These complementary
p-type and n-type nanofibers coassemble <i>via</i> hydrogen
bonding, charge-transfer complex, and electrostatic interactions to
generate highly uniform supramolecular n/p-coassembled 1D nanowires.
This molecular design ensures highly ordered arrangement of D–A
stacks within n/p-coassembled supramolecular nanowires. The supramolecular
n/p-coassembled nanowires were found to be formed by A–D–A
unit cells having an association constant (<i>K</i><sub>A</sub>) of 5.18 × 10<sup>5</sup> M<sup>–1</sup>. In
addition, electrical measurements revealed that supramolecular n/p-coassembled
nanowires are approximately 2400 and 10 times more conductive than
individual n-type and p-type nanofibers, respectively. This facile
strategy allows fabrication of well-defined supramolecular electroactive
nanomaterials in aqueous media, which can find a variety of applications
in optoelectronics, photovoltaics, organic chromophore arrays, and
bioelectronics
Biocompatible Electroactive Tetra(aniline)-Conjugated Peptide Nanofibers for Neural Differentiation
Peripheral
nerve injuries cause devastating problems for the quality of patients’
lives, and regeneration following damage to the peripheral nervous
system is limited depending on the degree of the damage. Use of nanobiomaterials
can provide therapeutic approaches for the treatment of peripheral
nerve injuries. Electroactive biomaterials, in particular, can provide
a promising cure for the regeneration of nerve defects. Here, a supramolecular
electroactive nanosystem with tetraÂ(aniline) (TA)-containing peptide
nanofibers was developed and utilized for nerve regeneration. Self-assembled
TA-conjugated peptide nanofibers demonstrated electroactive behavior.
The electroactive self-assembled peptide nanofibers formed a well-defined
three-dimensional nanofiber network mimicking the extracellular matrix
of the neuronal cells. Neurite outgrowth was improved on the electroactive
TA nanofiber gels. The neural differentiation of PC-12 cells was more
advanced on electroactive peptide nanofiber gels, and these biomaterials
are promising for further use in therapeutic neural regeneration applications