25 research outputs found
Surface-Enhanced Raman Spectroscopy-Based, Homogeneous, Multiplexed Immunoassay with Antibody-Fragments-Decorated Gold Nanoparticles
We report the development of a novel
single-step, multiplexed,
homogeneous immunoassay platform for sensitive detection of protein
targets based on our realization of high surface-enhanced raman spectroscopy
(SERS) signal enhancement by controlled assembly of SERS nanoparticles.
An essential design of this platform is the use of gold nanoparticles
or nanorods codecorated with specially reduced antibody half-fragments,
nonfluorescent Raman-active dyes, and passivating proteins as the
SERS nanoparticles. These nanoparticles offer a facile approach to
accomplish orientational immobilization of antibodies, minimized interparticle
distance, multicolor Raman fingerprint coding, low fluorescence background,
as well as excellent biocompatibility and stability. Through sandwiched
antibody–antigen interactions, controlled assembly of SERS
nanoparticles is realized with a strong SERS signal achieved via plasmonic
coupling, creating an immunoassay platform for rapid, sensitive, multiplexed
quantification of proteins. This platform is demonstrated for reproducible
quantification of three cytokines, interferon gamma, interleukin-2,
and tumor necrosis factor alpha, with large signal-to-noise ratio.
It is also successfully applied to multiplexed cytokine analysis for
T cell secretion studies in complicated biological samples. The developed
SERS immunoassay platform may create a simple but valuable tool for
facilitating accurate validation and early detection of disease biomarkers
as well as for point-of-care tests in clinical diagnostics
Enzymatic Immuno-Assembly of Gold Nanoparticles for Visualized Activity Screening of Histone-Modifying Enzymes
Activity screening of histone-modifying enzymes is of
paramount importance for epigenetic research as well as clinical diagnostics
and therapeutics. A novel biosensing strategy has been developed for
sensitive and selective detection of histone-modifying enzymes as
well as their inhibitors. This strategy relies on the antibody-mediated
assembly of gold nanoparticles (AuNPs) decorated with substrate peptides
that are subjected to enzymatic modifications by the histone-modifying
enzymes. This design allows a visual and homogeneous assay of the
enzyme activity using antibodies without any labels, which circumvents
the requirements to prefunctionalize the antibody and affords improved
assay simplicity and throughput. Additionally, the use of antibody-based
recognition of modified peptides could offer improved specificity
as compared with existing techniques based on the enzyme coupled assay.
We have demonstrated this strategy using a histone methyltransferase
acting on histone H3 (Lys 4) and a histone acetyltransferase acting
on histone H3 (Lys 14). The results reveal that the absorption peak
characteristic for AuNPs decreases dynamically with increasing activity
of the enzymes with concomitant visualizable color attenuation, and
subnanomolar detection limits are readily achieved for both enzymes.
The developed strategy can thus offer a robust and convenient visualized
platform for screening the enzyme activities and their inhibitors
with high sensitivity and selectivity
Enzymatic Control of Plasmonic Coupling and Surface Enhanced Raman Scattering Transduction for Sensitive Detection of DNA Demethylation
We have developed a novel concept for enzymatic control
of plasmonic
coupling as a surface enhanced Raman scattering (SERS) nanosensor
for DNA demethylation. This nanosensor is constructed by decorating
gold nanoparticles (AuNPs) with Raman reporters and hemimethylated
DNA probes. Demethylation of DNA probes initiates a degradation reaction
of the probes by methylation-sensitive endonuclease Bsh 1236I and
single-strand selective exonuclease I. This destabilizes AuNPs and
mediates the aggregation of AuNPs, generating a strong plasmonic coupling
SERS signal in response to DNA demethylation. This nanosensor has
the advantages in its high signal-to-noise ratio, superb specificity,
and rapid, convenient, and reproducible detection with homogeneous,
single-step operation. Thus, it provides a useful platform for detecting
DNA demethylation and related molecular diagnostics and drug screening.
This work is the first time that enzymatic degradation of DNA substrate
probes has been utilized to induce aggregation of AuNPs such that
reproducible, sensitive SERS signals can be achieved from biological
recognition events. This enzymatic control mechanism for plasmonic
coupling may create a new paradigm for the development of SERS nanosensors
Chemically Inducible DNAzyme Sensor for Controllable Imaging of Metal Ions
RNA-cleaving
DNAzymes have emerged as a promising tool for metal
ion detection. Achieving spatiotemporal control over their catalytic
activity is essential for understanding the role of metal ions in
various biological processes. While photochemical and endogenous stimuli-responsive
approaches have shown potential for controlled metal ion imaging using
DNAzymes, limitations such as photocytotoxicity, poor tissue penetration,
or off-target activation have hindered their application for safe
and precise detection of metal ions in vivo. We herein
report a chemically inducible DNAzyme in which the catalytic core
is modified to contain chemical caging groups at the selected backbone
sites through systematic screening. This inducible DNAzyme exhibits
minimal leakage of catalytic activity and can be reactivated by small
molecule selenocysteines, which effectively remove the caging groups
and restore the activity of DNAzyme. Benefiting from these findings,
we designed a fluorogenic chemically inducible DNAzyme sensor for
controlled imaging of metal ions with tunable activity and high selectivity
in live cells and in vivo. This chemically inducible
DNAzyme design expands the toolbox for controlling DNAzyme activity
and can be easily adapted to detect other metal ions in vivo by changing the DNAzyme module, offering opportunities for precise
biomedical diagnosis
Electrostatic Nucleic Acid Nanoassembly Enables Hybridization Chain Reaction in Living Cells for Ultrasensitive mRNA Imaging
Efficient
approaches for intracellular delivery of nucleic acid
reagents to achieve sensitive detection and regulation of gene and
protein expressions are essential for chemistry and biology. We develop
a novel electrostatic DNA nanoassembly that, for the first time, realizes
hybridization chain reaction (HCR), a target-initiated alternating
hybridization reaction between two hairpin probes, for signal amplification
in living cells. The DNA nanoassembly has a designed structure with
a core gold nanoparticle, a cationic peptide interlayer, and an electrostatically
assembled outer layer of fluorophore-labeled hairpin DNA probes. It
is shown to have high efficiency for cellular delivery of DNA probes
via a unique endocytosis-independent mechanism that confers a significant
advantage of overcoming endosomal entrapment. Moreover, electrostatic
assembly of DNA probes enables target-initialized release of the probes
from the nanoassembly via HCR. This intracellular HCR offers efficient
signal amplification and enables ultrasensitive fluorescence activation
imaging of mRNA expression with a picomolar detection limit. The results
imply that the developed nanoassembly may provide an invaluable platform
in low-abundance biomarker discovery and regulation for cell biology
and theranostics
Phospholipid–Graphene Nanoassembly as a Fluorescence Biosensor for Sensitive Detection of Phospholipase D Activity
A novel phospholipid–graphene nanoassembly is
developed
based on self-assembly of phospholipids on nonoxidative graphene surfaces.
The nanoassembly can be prepared easily through noncovalent hydrophobic
interactions between the lipid tails and the graphene without destroying
the electronic conjugation within the graphene sheet. This imparts
the nanoassembly with desired electrical and optical properties with
nonoxidative graphene. The phospholipid coating offers excellent biocompatibility,
facile solubilization, and controlled surface modification for graphene,
making the nanoassembly a useful platform for biofunctionalization
of graphene. The nanoassembly is revealed to comprise a bilayer of
phospholipids with a reduced graphene oxide sheet hosting in the hydrophobic
interior, thus affording a unique planar mimic of the cellular membrane.
By using a fluorescein-labeled phospholipid in this nanoassembly,
a fluorescence biosensor is developed for activity assay of phospholipase
D. The developed biosensor is demonstrated to have high sensitivity,
wide dynamic range, and very low detection limit of 0.010 U/L. Moreover,
because of its single-step homogeneous assay format it displays excellent
robustness, improved assay simplicity and throughput, as well as intrinsic
ability to real-time monitor the reaction kinetics
Activity-Based DNA-Gold Nanoparticle Probe as Colorimetric Biosensor for DNA Methyltransferase/Glycosylase Assay
We
have developed a novel biosensor platform for colorimetric detection
of active DNA methyltransferase/glycosylase based on terminal protection
of the DNA-gold nanoparticle (AuNP) probes by mechanistically covalent
trapping of target enzymes. This biosensor relied on covalent capture
of target enzymes by activity-based DNA probes which created terminal
protection of the DNA probes tethered on AuNPs from degradation by
Exo I and III. This biosensor has the advantages of having highly
sensitive, rapid, and convenient detection due to its use of the homogeneous
assay format and strong surface plasmon absorption. Because the activity-based
probes (ABPs) are mechanistically specific to target enzymes, this
strategy also offers improved selectivity and can achieve the information
about both abundance and activity of the enzymes. We have demonstrated
this strategy using a human DNA (cytosine-5) methyltransferase (Dnmt
1) and a human 8-oxoguanine glycosylase (hOGG 1). The results reveal
that the colorimetric response increases dynamically with increasing
activity of the enzymes, implying a great potential of this strategy
for DNA methyltransferase/glycosylase detection and molecular diagnostics
and drug screening. Our strategy can also be used as a promising and
convenient approach for visualized screening of ABPs for DNA modifying
enzymes
Genetically Encoded Fluorescent RNA Sensor for Ratiometric Imaging of MicroRNA in Living Tumor Cells
Light-up
RNA aptamers are valuable tools for fluorescence imaging of RNA in
living cells and thus for elucidating RNA functions and dynamics.
However, no light-up RNA sensor has been reported for imaging of microRNAs
(miRs) in mammalian cells. We report a novel genetically encoded RNA
sensor for fluorescent imaging of miRs in living tumor cells using
a light-up RNA aptamer that binds to sulforhodamine and separates
it from a conjugated contact quencher. On the basis of the structural
switching mechanism for molecular beacon, we show that the RNA sensor
activates high-contrast fluorescence from the sulforhodamine-quencher
conjugate when its stem–loop responsive motif hybridizes with
target miR. The RNA sensor can be stably expressed within a designed
tRNA scaffold in tumor cells and deliver light-up response to miR
target. We also realize the RNA sensor for dual-emission, ratiometric
imaging by coexpression of RNA sensor with GFP, enabling quantitative
studies of target miR in living cells. Our design may provide a new
paradigm for developing robust, sensitive light-up RNA sensors for
RNA imaging applications
In Situ Imaging of Individual mRNA Mutation in Single Cells Using Ligation-Mediated Branched Hybridization Chain Reaction (Ligation-bHCR)
Ultrasensitive
and
specific in situ imaging of gene expression
is essential for molecular medicine and clinical theranostics. We
develop a novel fluorescence in situ hybridization (FISH) strategy
based on a new branched hybridization chain reaction (bHCR) for efficient
signal amplification in the FISH assay and a ligase-mediated discrimination
for specific mutation detection. To our knowledge, this is the first
time that HCR has been realized for mutation detection in the FISH
assay. In vitro assay shows that the ligation-bHCR strategy affords
high specificity in discriminating single-nucleotide variation in
mRNA, and it generates a highly branched polymeric product that confers
more efficient amplification or better sensitivity than HCR. Imaging
analysis reveals that ligation-bHCR generates highly bright spot-like
signals for localization of individual mRNA molecules, and spot signals
of different colors are highly specific in genotyping point mutation
of individual mRNA. Moreover, this strategy is shown to have the potential
for quantitative imaging of the expression of mRNA at the single-cell
level. Therefore, this strategy may provide a new promising paradigm
in developing highly sensitive and specific FISH methods for various
diagnostic and research applications
Peptide-Templated Gold Nanocluster Beacon as a Sensitive, Label-Free Sensor for Protein Post-translational Modification Enzymes
Protein post-translational modifications
(PTMs), which are chemical
modifications and most often regulated by enzymes, play key roles
in functional proteomics. Detection of PTM enzymes, thus, is critical
in the study of cell functioning and development of diagnostic and
therapeutic tools. Herein, we develop a simple peptide-templated method
to direct rapid synthesis of highly fluorescent gold nanoclusters
(AuNCs) and interrogate the effect of enzymatic modifications on their
luminescence. A new finding is that enzymes are able to exert chemical
modifications on the peptide-templated AuNCs and quench their fluorescence,
which furnishes the development of a real-time and label-free sensing
strategy for PTM enzymes. Two PTM enzymes, histone deacetylase 1 and
protein kinase A, have been employed to demonstrate the feasibility
of this enzyme-responsive fluorescent nanocluster beacon. The results
reveal that the AuNCs’ fluorescence can be dynamically decreased
with increasing concentration of the enzymes, and subpicomolar detection
limits are readily achieved for both enzymes. The developed strategy
can thus offer a useful, label-free biosensor platform for the detection
of protein-modifying enzymes and their inhibitors in biomedical applications