11 research outputs found
Flexible Narrowband Ultraviolet Photodetectors with Photomultiplication Based on Wide Band Gap Conjugated Polymer and Inorganic Nanoparticles
Lightweight and flexible ultraviolet
(UV) photodetectors (PDs) have wide applications and have attracted
more attention. PDs using organic and inorganic nanocomposites as
active layers with a photodiode configuration could achieve photomultiplication
and narrowband photoresponse via the control of microstructure and
thickness of active layers. Here, we fabricated flexible UV PDs on
indium tin oxide-coated poly(ethylene terephthalate) substrates with
a nanocomposite active layer composed of ZnO nanoparticles blended
with a wide band gap conjugated polymer, poly[(9,9-dioctylfluorenyl-2,7-diyl)-<i>alt</i>-<i>co</i>-(bithiophene)] (F8T2). As a result
of the wavelength-dependent penetration depth of light in the active
layer, the fabricated flexible UV PDs showed two narrow response peaks
at 360 and 510 nm under reverse biases in the external quantum efficiency
(EQE) spectra with full width at half maximum (FWHM) less than 20
nm. Both responses exhibited greater than 100% EQE, indicating a photomultiplication
effect, whereas the UV response at 360 nm was 10 times stronger under
−15 V bias. The fabricated flexible UV PDs were bent under
both tensile and compressive stress to a curvature of 2.1 cm<sup>–1</sup>, each with 50 repetitions. The peak specific detectivity (<i>D</i>*) only decreased by about 5% in total, the FWHM was well
retained below 20 nm and the response speed remained almost constant
after two types of bending, demonstrating mechanical flexibility and
photoresponse stability of the fabricated flexible UV PDs. The photodiode
configuration with nanocomposite active layers offers a promising
route to make flexible and conformable narrowband, photomultiplication-type
photodetectors for modern applications
Directly Functionalizable Surface Platform for Protein Arrays in Undiluted Human Blood Plasma
Protein arrays are a high-throughput approach for proteomic
profiling,
vital for achieving a greater understanding of biological systems,
in addition to disease diagnostics and monitoring therapeutic treatments.
In this work, zwitterionic carboxybetaine polymer (pCB) coated substrates
were investigated as an array surface platform to enable convenient
amino-coupling chemistry on a single directly functionalizable and
unblocked film for the sensitive detection of target analytes from
undiluted human blood plasma. Using a surface plasmon resonance (SPR)
imaging sensor, the antibody immobilization conditions which provided
excellent spot morphology and the largest antigen response were determined.
It was found that pCB functionalization and the corresponding antigen
detection both increased with pH and antibody concentration. Additionally,
immobilization only required an aqueous buffer without the need for
additives to improve spot quality. The nonspecific protein adsorption
to undiluted human plasma on both the antibody immobilized pCB spots
and the background were found to be about 9 and 6 ng/cm<sup>2</sup>, respectively. A subsequent array consisting of three antibodies
spotted onto pCB revealed little cross-reactivity for antigens spiked
into the undiluted plasma. The low postfunctionalized nonfouling properties
combined with antibody amplification showed similar sensitivities
achievable with conventional spectroscopic SPR sensors and the same
pCB films, but now with high-throughput capabilities. This represents
the first demonstration of low fouling properties following antibody
functionalization on protein arrays from undiluted human plasma and
indicates the great potential of the pCB platform for high-throughput
protein analysis
Surface-Enhanced Raman Scattering on Gold Nanohole Arrays in Symmetrical Dielectric Environments Exhibiting Electric Field Extension
The electromagnetic enhancement in
surface-enhanced Raman scattering
(SERS) caused by localized surface plasmon resonance is a near-field
effect, often limiting the practicality of SERS in many applications.
However, no attempts have been made to investigate field extension
through symmetrical refractive index modulation in a SERS-based system.
Here, we report the development and characterization of refractive
index-matched SERS substrates supporting electric field extension
to realize what is termed “long-range SERS” (LR-SERS).
Finite-difference time-domain simulations were employed to tune the
plasmonic responses and investigate electric field distributions of
gold nanohole arrays (NHAs) as a function of the dielectric environment
and geometric parameters. SERS substrates supporting long-range behavior
were compared against “conventional” substrates without
long-range behavior. SERS intensities from rhodamine 6G (R6G) aqueous
solutions of 2.0 × 10<sup>3</sup> and 1.5 × 10<sup>2</sup> counts s<sup>–1</sup> mW<sup>–1</sup> were produced by the LR-SERS and conventional substrates, respectively,
on the gold surface. Moreover, a signal response of 9.0 × 10<sup>1</sup> counts s<sup>–1</sup> mW<sup>–1</sup> was produced by LR-SERS substrates with a 10 nm separation between
the R6G solution and NHA, while no signal was observed from the conventional
substrate. As a proof of principle study, the results demonstrate
the potential to use LR-SERS substrates in applications where the
target analyte is located further from the SERS-active surface
Two-Layer Architecture Using Atom Transfer Radical Polymerization for Enhanced Sensing and Detection in Complex Media
A novel, two-layer hierarchical architecture based on
surface-initiated
atom transfer radical polymerization was investigated. It combines
a thin and highly dense first layer, for nonfouling properties, with
a loose second layer for high immobilization levels of active biomolecules.
Sodium azide treatment, to reduce the concentration of macroinitiators
on the first layer for reinitiation, and by controlling the polydispersity
allowed one to achieve three polymer architectures with low, moderate,
or high azide substitution. Moderate substitution enabled the highest
immobilization levels with a nonfouling background. Integration with
dual-functional zwitterionic poly(carboxybetaine) made this platform
suitable for applications in undiluted complex media such as blood.
It was demonstrated via a surface plasmon resonance biosensor that
antigen accessibility and antibody loading were greatly improved.
These results indicate the two-layer strategy as a generic concept
suitable for applications from diagnostics to medical coatings in
order to maximize and minimize specific and nonspecific responses,
respectively
Dry Film Refractive Index as an Important Parameter for Ultra-Low Fouling Surface Coatings
Here we demonstrate that the film refractive index (RI)
can be
an even more important parameter than film thickness for identifying
nonfouling polymer films to undiluted human blood plasma and serum.
The film thickness and RI
are two parameters obtained from ellipsometry. Previously, film thickness
has been correlated to ultra-low fouling properties. Practically,
the film RI can be used to characterize polymer density but is often
overlooked. By varying the water content in the surface-initiated
atom transfer radical polymerization of zwitterionic carboxybetaine,
a minimum of ∼1.5 RI units was necessary to achieve <5 ng/cm<sup>2</sup> of adsorption from undiluted human serum. A model of the
film structure versus water content was also developed. These results
point to an important parameter and simple approach for identifying
surface coatings suitable for real-world applications involving complex
media. Therefore, ultra-low fouling using a thin film is possible
if it is densely packed
A Robust Graft-to Strategy To Form Multifunctional and Stealth Zwitterionic Polymer-Coated Mesoporous Silica Nanoparticles
Mesoporous silica nanoparticles (MSNs) are a new class of carrier
materials promising for drug/gene delivery and many other important
applications. Stealth coatings are necessary to maintain their stability
in complex media. Herein, a biomimetic polymer conjugate containing
one ultralow fouling poly(carboxybetaine) (pCBMA) chain and one surface-adhesive
catechol (DOPA) residue group was efficiently grafted to the outer
surface of SBA-15 type MSNs using a convenient and robust method.
The cytotoxicity of SBA-15-DOPA-pCBMAs was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide (MTT) assay. Results showed no significant decrease in cell
viability at the tested concentration range. Macrophage cell uptake
studies revealed that the uptake ratios of SBA-15-DOPA-pCBMAs were
much lower than that of parent MSNs. Furthermore, inductively coupled
plasma mass spectrometry (ICP-MS) analysis results showed that after
SBA-15-DOPA-pCBMAs were conjugated with a targeting cyclo-[Arg-Gly-Asp-d-Tyr-Lys] (cRGD) peptide, uptake by bovine aortic endothelial
cells (BAECs) was notably increased. Results indicated that cRGD-functionalized
MSNs were able to selectively interact with cells expressing αvβ3
integrin. Thus, MSNs with DOPA-pCBMAs are promising as stealth multifunctional
biocarriers for targeted drug delivery or diagnostics
Sensitive and Fast Detection of Fructose in Complex Media via Symmetry Breaking and Signal Amplification Using Surface-Enhanced Raman Spectroscopy
A new
strategy is proposed to sensitively and rapidly detect analytes
with weak Raman signals in complex media using surface-enhanced Raman
spectroscopy (SERS) via detecting the SERS signal changes of the immobilized
probe molecules on SERS-active substrates upon binding of the analytes.
In this work, 4-mercaptophenylboronic acid (4-MPBA) was selected as
the probe molecule which was immobilized on the gold surface of a
quasi-three-dimensional plasmonic nanostructure array (Q3D-PNA) SERS
substrate to detect fructose. The molecule of 4-MPBA possesses three
key functions: molecule recognition and reversible binding of the
analyte via the boronic acid group, amplification of SERS signals
by the phenyl group and thus shielding of the background noise of
complex media, and immobilization on the surface of SERS-active substrates
via the thiol group. Most importantly, the symmetry breaking of the
4-MPBA molecule upon fructose binding leads to the change of area
ratio between totally symmetric 8a ring mode and nontotally symmetric
8b ring mode, which enables the detection. The detection curves were
obtained in phosphate-buffered saline (PBS) and in undiluted artificial
urine at clinically relevant concentrations, and the limit of detection
of 0.05 mM was achieved
Stealth Surface Modification of Surface-Enhanced Raman Scattering Substrates for Sensitive and Accurate Detection in Protein Solutions
Reliable surface-enhanced Raman scattering (SERS) based biosensing in complex media is impeded by nonspecific protein adsorptions. Because of the near-field effect of SERS, it is challenging to modify SERS-active substrates using conventional nonfouling materials without introducing interference from their SERS signals. Herein, we report a stealth surface modification strategy for sensitive, specific and accurate detection of fructose in protein solutions using SERS by forming a mixed self-assembled monolayer (SAM). The SAM consists of a short zwitterionic thiol, <i>N</i>,<i>N</i>-dimethyl-cysteamine-carboxybetaine (CBT), and a fructose probe 4-mercaptophenylboronic acid (4-MPBA). The specifically designed and synthesized CBT not only resists protein fouling effectively, but also has very weak Raman activity compared to 4-MPBA. Thus, the CBT SAM provides a stealth surface modification to SERS-active substrates. The surface compositions of mixed SAMs were investigated using X-ray photoelectron spectroscopy (XPS) and SERS, and their nonfouling properties were studied with a surface plasmon resonance (SPR) biosensor. The mixed SAM with a surface composition of 94% CBT demonstrated a very low bovine serum albumin (BSA) adsorption (∼3 ng/cm<sup>2</sup>), and moreover, only the 4-MPBA signal appeared in the SERS spectrum. With the use of this surface-modified SERS-active substrate, quantification of fructose over clinically relevant concentrations (0.01–1 mM) was achieved. Partial least-squares regression (PLS) analysis showed that the detection sensitivity and accuracy were maintained for the measurements in 1 mg/mL BSA solutions. This stealth surface modification strategy provides a novel route to introduce nonfouling property to SERS-active substrates for SERS biosensing in complex media
Cellulose Paper Sensors Modified with Zwitterionic Poly(carboxybetaine) for Sensing and Detection in Complex Media
Poly(carboxybetaine) (PCB) functionalized
cellulose paper was used
as a paper-based microfluidic device. The results showed that the
PCB modified paper sensor was able to achieve (a) more rapid and sensitive
glucose detection from undiluted human serum compared to bare cellulose
and (b) specific antigen detection via covalently immobilized antibodies
Simple Physical Approach to Reducing Frictional and Adhesive Forces on a TiO<sub>2</sub> Surface via Creating Heterogeneous Nanopores
A simple physical strategy to reduce the frictional and
adhesive
forces on TiO<sub>2</sub> films was proposed by constructing mesoporous
TiO<sub>2</sub> films with heterogeneously distributed nanopores on
the film surfaces. In comparison, TiO<sub>2</sub> films with densely
packed nanoparticles were also prepared. The crystal structure and
morphology of the films were characterized with Raman spectroscopy,
field emission scanning electron microscopy (FESEM), and atomic force
microscopy (AFM). It was found that the TiO<sub>2</sub>(B) phase exists
in the mesoporuos TiO<sub>2</sub> films but not in the densely packed
films. The existence of TiO<sub>2</sub>(B) plays a significant role
in creating and maintaining the nanopores in the mesoporous TiO<sub>2</sub> films. The frictional and adhesive forces were measured on
both films using AFM. The mesoporous films exhibit two typical adhesion
forces of around 3 and 12 nN in the force distribution profile whereas
the densely packed films show only one around 12 nN. The frictional
coefficients were 2.6 × 10<sup>–3</sup> and 6.7 ×
10<sup>–2</sup> for the mesoporous and densely packed TiO<sub>2</sub> films, respectively. A model based on the atomic structures
of a thin film of water molecules adsorbed on TiO<sub>2</sub> surfaces
leading to hydrophobic effects was proposed to understand the lower
frictional and adhesive forces observed on the mesoporous TiO<sub>2</sub> films. This simple physical approach to reducing the frictional
and adhesive forces on TiO<sub>2</sub> films could have broad applications
to a variety of surface coatings