12 research outputs found
Pd@Pt Nanodendrites as Peroxidase Nanomimics for Enhanced Colorimetric ELISA of Cytokines with Femtomolar Sensitivity
Colorimetric enzyme-linked immunosorbent assay (ELISA) has been widely applied as the gold-standard method for cytokine detection for decades. However, it has become a critical challenge to further improve the detection sensitivity of ELISA, as it is limited by the catalytic activity of enzymes. Herein, we report an enhanced colorimetric ELISA for ultrasensitive detection of interleukin-6 (IL-6, as a model cytokine for demonstration) using Pd@Pt core@shell nanodendrites (Pd@Pt NDs) as peroxidase nanomimics (named āPd@Pt ND ELISAā), pushing the sensitivity up to femtomolar level. Specifically, the Pd@Pt NDs are rationally engineered by depositing Pt atoms on Pd nanocubes (NCs) to generate rough dendrite-like Pt skins on the Pd surfaces via VolmerāWeber growth mode. They can be produced on a large scale with highly uniform size, shape, composition, and structure. They exhibit significantly enhanced peroxidase-like catalytic activity with catalytic constants (Kcat) more than 2000-fold higher than those of horseradish peroxidase (HRP, an enzyme commonly used in ELISA). Using Pd@Pt NDs as the signal labels, the Pd@Pt ND ELISA presents strong colorimetric signals for the quantitative determination of IL-6 with a wide dynamic range of 0.05ā100 pg mLā1 and an ultralow detection limit of 0.044 pg mLā1 (1.7 fM). This detection limit is 21-fold lower than that of conventional HRP-based ELISA. The reproducibility and specificity of the Pd@Pt ND ELISA are excellent. More significantly, the Pd@Pt ND ELISA was validated for analyzing IL-6 in human serum samples with high accuracy and reliability through recovery tests. Our results demonstrate that the colorimetric Pd@Pt ND ELISA is a promising biosensing tool for ultrasensitive determination of cytokines and thus is expected to be applied in a variety of clinical diagnoses and fundamental biomedical studies
A non-enzyme cascade amplification strategy for colorimetric assay of disease biomarkers
Ā© 2017 The Royal Society of Chemistry. A non-enzyme cascade amplification strategy, based on the dissolution of Ag nanoparticles and a Pt nanocube-catalyzed reaction, for colorimetric assay of disease biomarkers was developed. This strategy overcomes the intrinsic limitations of enzymes involved in conventional enzymatic amplification techniques, thanks to the utilization of noble-metal nanostructures with superior properties
Target-Induced Nanocatalyst Deactivation Facilitated by Core@Shell Nanostructures for Signal-Amplified Headspace-Colorimetric Assay of Dissolved Hydrogen Sulfide
Colorimetric
assay platforms for dissolved hydrogen sulfide (H<sub>2</sub>S) have
been developed for more than 100 years, but most still suffer from
relatively low sensitivity. One promising route out of this predicament
relies on the design of efficient signal amplification methods. Herein,
we rationally designed an unprecedented H<sub>2</sub>S-induced deactivation
of (gold core)@(ultrathin platinum shell) nanocatalysts (Au@TPt-NCs)
as a highly efficient signal amplification method for ultrasensitive
headspace-colorimetric assay of dissolved H<sub>2</sub>S. Upon target
introduction, Au@TPt-NCs were deactivated to different degrees dependent
on H<sub>2</sub>S levels, and the degrees could be indicated by using
a Au@TPt-NCs-triggered catalytic system as a signal amplifier, thus
paving a way for H<sub>2</sub>S sensing. The combination of experimental
studies and density functional theory (DFT) studies revealed that
the Au@TPt-NCs with only 2-monolayer equivalents of Pt (Īø<sub>Pt</sub> = 2) were superior for H<sub>2</sub>S-induced nanocatalyst
deactivation owing to their enhanced peroxidase-like catalytic activity
and deactivation efficiency stemmed from the unique synergistic structural/electronic
effects between Au nanocores and ultrathin Pt nanoshells. Importantly,
our analytical results showed that the designed method was indeed
highly sensitive for sensing H<sub>2</sub>S with a wide linear range
of 10ā100 nM, a slope of 0.013 in the regression equation,
and a low detection limit of 7.5 nM. Also the selectivity, reproducibility,
and precision were excellent. Furthermore, the method was validated
for the analysis of H<sub>2</sub>S-spiked real samples, and the recovery
in all cases was 91.6ā106.7%. With the merits of high sensitivity
and selectivity, simplification, low cost, and visual readout with
the naked eye, the colorimetric method has the potential to be utilized
as an effective detection kit for point-of-care testing
High-Resolution Colorimetric Assay for Rapid Visual Readout of Phosphatase Activity Based on Gold/Silver Core/Shell Nanorod
Nanostructure-based visual assay
has been developed for determination
of enzymatic activity, but most involve in poor visible color resolution
and are not suitable for routine utilization. Herein, we designed
a high-resolution colorimetric protocol based on gold/silver core/shell
nanorod for visual readout of alkaline phosphatase (ALP) activity
by using bare-eyes. The method relied on enzymatic reaction-assisted
silver deposition on gold nanorod to generate significant color change,
which was strongly dependent on ALP activity. Upon target ALP introduction
into the substrate, the ascorbic acid 2-phosphate was hydrolyzed to
form ascorbic acid, and then, the generated ascorbic acid reduced
silver ion to metal silver and coated on the gold nanorod, thereby
resulting in the blue shift of longitudinal localized surface plasmon
resonance peak of gold nanorod accompanying a perceptible color change
from red to orange to yellow to green to cyan to blue and to violet.
Under optimal conditions, the designed method exhibited the wide linear
range 5ā100 mU mL<sup>ā1</sup> ALP with a detection
limit of 3.3 mU mL<sup>ā1</sup>. Moreover, it could be used
for the semiquantitative detection of ALP from 20 to 500 mU mL<sup>ā1</sup> by using the bare-eyes. The coefficients of variation
for intra- and interassay were below 3.5% and 6.2%, respectively.
Finally, this method was validated for the analysis of real-life serum
samples, giving results matched well with those from the 4-nitrophenyl
phosphate disodium salt hexahydrate (pNPP)-based standard method.
In addition, the system could even be utilized in the enzyme-linked
immunosorbent assay (ELISA) to detect IgG at picomol concentration.
With the merits of simplification, low cost, user-friendliness, and
sensitive readout, the gold nanorod-based colorimetric assay has the
potential to be utilized by the public and opens a new horizon for
bioassays
Facile Colorimetric Detection of Silver Ions with Picomolar Sensitivity
Although
various colorimetric methods have been actively developed
for the detection of Ag<sup>+</sup> ions because of their simplicity
and reliability, the limits of detection of these methods are confined
to the nanomolar (nM) level. Here, we demonstrate a novel strategy
for colorimetric Ag<sup>+</sup> detection with picomolar (pM) sensitivity.
This strategy involves the use of polyĀ(vinylpyrrolidone)- (PVP-) capped
Pt nanocubes as artificial peroxidases that can effectively generate
a colored signal by catalyzing the oxidation of peroxidase substrates.
In the presence of Ag<sup>+</sup> ions, the colored signal generated
by these Pt cubes is greatly diminished because of the specific and
efficient inhibition of Ag<sup>+</sup> toward the peroxidase-like
activity of the Pt cubes. This colorimetric method can achieve an
ultralow detection limit of 80 pM and a wide dynamic range of 10<sup>ā2</sup>ā10<sup>4</sup> nM. To the best of our knowledge,
the method presented in this work shows the highest sensitivity for
Ag<sup>+</sup> detection among all reported colorimetric methods.
Moreover, this method also features simplicity and rapidness as it
can be conducted at room temperature, in aqueous solution, and requires
only ā¼6 min
Platinum-Decorated Gold Nanoparticles with Dual Functionalities for Ultrasensitive Colorimetric in Vitro Diagnostics
Au
nanoparticles (AuNPs) as signal reporters have been utilized
in colorimetric in vitro diagnostics (IVDs) for decades. Nevertheless,
it remains a grand challenge to substantially enhance the detection
sensitivity of AuNP-based IVDs as confined by the inherent plasmonics
of AuNPs. In this work, we circumvent this confinement by developing
unique dual-functional AuNPs that were engineered by coating conventional
AuNPs with ultrathin Pt skins of sub-10 atomic layers (i.e., Au@Pt
NPs). The Au@Pt NPs retain the plasmonic activity of initial AuNPs
while possessing ultrahigh catalytic activity enabled by Pt skins.
Such dual functionalities, plasmonics and catalysis, offer two different
detection alternatives: one produced just by the color from plasmonics
(low-sensitivity mode) and the second more sensitive color catalyzed
from chromogenic substrates (high-sensitivity mode), achieving an
āon-demandā tuning of the detection performance. Using
lateral flow assay as a model IVD platform and conventional AuNPs
as a benchmark, we demonstrate that the Au@Pt NPs could enhance detection
sensitivity by 2 orders of magnitude
Strain Effect in Palladium Nanostructures as Nanozymes
While various effects of physicochemical parameters (e.g., size, facet, composition, and internal structure) on the catalytic efficiency of nanozymes (i.e., nanoscale enzyme mimics) have been studied, the strain effect has never been reported and understood before. Herein, we demonstrate the strain effect in nanozymes by using Pd octahedra and icosahedra with peroxidase-like activities as a model system. Strained Pd icosahedra were found to display 2-fold higher peroxidase-like catalytic efficiency than unstrained Pd octahedra. Theoretical analysis suggests that tensile strain is more beneficial to OH radical (a key intermediate for the catalysis) generation than compressive strain. Pd icosahedra are more active than Pd octahedra because icosahedra amplify the surface strain field. As a proof-of-concept demonstration, the strained Pd icosahedra were applied to an immunoassay of biomarkers, outperforming both unstrained Pd octahedra and natural peroxidases. The findings in this research may serve as a strong foundation to guide the design of high-performance nanozymes