9 research outputs found
Bifunctional Colorimetric Oligonucleotide Probe Based on a G-Quadruplex DNAzyme Molecular Beacon
A label-free bifunctional colorimetric oligonucleotide probe for DNA and protein detection has been developed on the basis of a novel catalytic molecular beacon consisting of two hairpin structures and a split G-quadruplex DNAzyme in the middle. The two loops of this molecular beacon consist of thrombin aptamer sequence and the complementary sequence of target DNA, which are utilized to sense single-stranded DNA and thrombin. The G-quadruplex DNAzyme can effectively catalyze the H<sub>2</sub>O<sub>2</sub>-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine sulfate to generate colorimetric signal. Upon addition of the target, the DNA or protein combines with one loop of the hairpin structures, and meanwhile drives the middle G-quadruplex DNAzyme to dissociate. This results in a decrease of catalytic activity, enabling the separate analysis of DNA and thrombin
Four-Way Junction-Driven DNA Strand Displacement and Its Application in Building Majority Logic Circuit
We introduced a four-way DNA junction-driven toehold-mediated strand displacement method. Separation of the different functional domains on different strands in the four-way junction structure and usage of glue strand to recombine them for different logic gates make the design more flexible. On the basis of this mechanism, a majority logic circuit fabricated by DNA strands was designed and constructed by assembling three AND gates and one OR gate together. The output strand drew the G-rich segments together to form a split G-quadruplex, which could specifically bind PPIX and enhance its fluorescence. Just like a poll with three voters, the high fluorescence signal would be given off only when two or three voters vote in favor. Upon slight modification, the majority circuit was utilized to select the composite number from 0 to 9 represented by excess-three code. It is a successful attempt to integrate the logic gates into a circuit and to achieve desired functions
Simple and Sensitive Fluorescent and Electrochemical Trinitrotoluene Sensors Based on Aqueous Carbon Dots
Aqueous
N-rich carbon dots (CDs), prepared by the microwave-assisted pyrolysis
method, are applied as a dual sensing platform for both the fluorescent
and electrochemical detection of 2,4,6-trinitrotoluene (TNT). The
fluorescent sensing platform is established on the strong TNT–amino
interaction which can quench the photoluminescence of amino functionalized
CDs through charge transfer. The resultant linear detection ranges
from 10 nM to 1.5 ÎĽM with a fast response time of 30 s. Glassy
carbon electrode modified with CDs exhibits a fine capability for
TNT reduction with the linear range from 5 nM to 30 ÎĽM, better
than that obtained by the fluorescent method. Moreover, the minimum
distinguishable response concentration with respect to these two methods
is down to the nanomolar level with a high specificity and sensitivity
Aptamer-Based Sensing Platform Using Three-Way DNA Junction-Driven Strand Displacement and Its Application in DNA Logic Circuit
We
proposed a new three-way DNA junction-driven strand displacement mode
and fabricated an aptamer-based label-free fluorescent sensing platform
on the basis of this mechanism. Assembling the aptamer sequence into
the three-way DNA junction makes the platform sensitive to the target
of the aptamer. A label-free signal readout method, split G-quadruplex
enhanced fluorescence of protoporphyrin IX (PPIX), was used to report
the final signal. Here, adenosine triphosphatase (ATP) was taken as
a model and detected through this approach, and DNA strand could also
be detected by it. The mechanism was investigated by native polyacrylamide
gel electrophoresis. Furthermore, on the basis of this molecular platform,
we built a logic circuit with ATP and DNA strands as input. Aptamer
played an important role in mediating the small molecule ATP to tune
the DNA logic gate. Through altering the aptamer sequence, this molecular
platform will be sensitive to various stimuli and applied in a wide
field
G‑quadruplex-Based Fluorescent Assay of S1 Nuclease Activity and K<sup>+</sup>
Endonuclease plays an important role in many biological
processes,
and an assay of endonuclease activity is of great significance. However,
traditional methods for the assay of endonuclease activity have undesirable
limitations, such as high cost, DNA-consuming and laboriousness. In
the present work, a G-quadruplex-based, fluorescent assay of endonuclease
activity has been developed with protoporphyrin IX (PPIX) as a signal
reporter. S1 nuclease, a single strand DNA (ssDNA)-specific endonuclease,
is employed as model system. In the “on” state, G-quadruplex
DNA can greatly enhance the fluorescence of PPIX. However, if S1 nuclease
could cleave G-quadruplex DNA into small fragments, there would be
no formation of G-quadruplexes, accompanied by low emission response
of PPIX. This fluorescent discrimination before or after digestion
by nuclease can be used to monitor the activity of S1 nuclease. This
assay is simple in design and offers a convenient protocol for homogeneous,
rapid and high-throughput detection. In addition, the proposed strategy
avoids complicated covalent modifications or chemical labeling, and
thus offers advantages of simplicity and cost efficiency. More importantly,
K<sup>+</sup> is found to well inhibit the activity of S1 nuclease
when using certain G-quadruplex DNA as substrate, and thus this system
is further used for turn-on detection of K<sup>+</sup>. S1 nuclease
is critical in the detection of K<sup>+</sup> since it helps to reduce
the background signal
Photoinduced Electron Transfer of DNA/Ag Nanoclusters Modulated by G‑Quadruplex/Hemin Complex for the Construction of Versatile Biosensors
Photoinduced electron transfer (PET) has been observed
for the
first time between DNA/Ag fluorescent nanoclusters (NCs) and G-quadruplex/hemin
complexes, accompanied by a decrease in the fluorescence of the DNA/Ag
NCs. In this PET process, a parallel G-quadruplex and the sensing
sequences are blocked by a duplex. The specific combination of targets
with the sensing sequence triggers the release of the G-quadruplex
and allows it to fold properly and bind hemin to form a stable G-quadruplex/hemin
complex. The complex proves favorable for PET because it makes the
G-quadruplex bind hemin tightly, which promotes the electron transfer
from the DNA/Ag NCs to the hemin Fe<sup>III</sup> center, thus resulting
in a decrease in the fluorescence intensity of the DNA/Ag NCs. This
novel PET system enables the specific and versatile detection of target
biomolecules such as DNA and ATP with high sensitivity based on the
choices of different target sequences
Lighting Up the Thioflavin T by Parallel-Stranded TG(GA)<i>n</i> DNA Homoduplexes
Thioflavin T (ThT) was once regarded
to be a specific fluorescent
probe for the human telomeric G-quadruplex, but more other kinds of
DNA were found that can also bind to ThT in recent years. Herein,
we focus on G-rich parallel-stranded DNA and utilize fluorescence,
absorbance, circular dichroism, and surface plasmon resonance spectroscopy
to investigate its interaction with ThT. Pyrene label and molecular
modeling are applied to unveil the binding mechanism. We find a new
class of non-G-quadruplex G-rich parallel-stranded (<i>ps</i>) DNA with the sequence of TGÂ(GA)<i>n</i> can bind to ThT
and increase the fluorescence with an enhancement ability superior
to G-quadruplex. The optimal binding specificity for ThT is conferred
by two parts. The first part is composed of two bases TG at the 5′
end, which is a critical domain and plays an important role in the
formation of the binding site for ThT. The second part is the rest
alternative dÂ(GA) bases, which forms the <i>ps</i> homoduplex
and cooperates with the TG bases at the 5′ end to bind the
ThT
Graphene-Based Aptamer Logic Gates and Their Application to Multiplex Detection
In this work, a GO/aptamer system was constructed to create multiplex logic operations and enable sensing of multiplex targets. 6-Carboxyfluorescein (FAM)-labeled adenosine triphosphate binding aptamer (ABA) and FAM-labeled thrombin binding aptamer (TBA) were first adsorbed onto graphene oxide (GO) to form a GO/aptamer complex, leading to the quenching of the fluorescence of FAM. We demonstrated that the unique GO/aptamer interaction and the specific aptamer–target recognition in the target/GO/aptamer system were programmable and could be utilized to regulate the fluorescence of FAM <i>via</i> OR and INHIBIT logic gates. The fluorescence changed according to different input combinations, and the integration of OR and INHIBIT logic gates provided an interesting approach for logic sensing applications where multiple target molecules were present. High-throughput fluorescence imagings that enabled the simultaneous processing of many samples by using the combinatorial logic gates were realized. The developed logic gates may find applications in further development of DNA circuits and advanced sensors for the identification of multiple targets in complex chemical environments
Engineering DNA Three-Way Junction with Multifunctional Moieties: Sensing Platform for Bioanalysis
Functionalization of DNA nanostructures
is critical to the achievement
of the application in biosensors. Herein, we demonstrate a novel DNA
three-way junction (TWJ) with three functional moieties, which integrates
the electrochemical, fluorescent, and colorimetric properties. Upon
addition of external stimuli, including DNA, thrombin, and ATP, the
specific interactions between targets and sensing elements could induce
strand displacement reaction and conformation transformation, resulting
in the integration of G-quadruplex/hemin complex as electrochemical
probe, lighting up the fluorescence of DNA/Ag nanoclusters and enhancing
the catalytic activity of DNAzyme to catalyze the H<sub>2</sub>O<sub>2</sub>–TMB system to generate colorimetric signal. Such a
functional DNA nanostructure actually serves as a biosensing platform,
showing high sensitivity and selectivity for DNA, thrombin, and ATP
detection. Furthermore, We also show that this novel sensing platform
can be utilized to detect three different kinds of targets independently
and simultaneously. Our integrated concept provides a paradigm for
exploring the potential of TWJs in analytical applications