6 research outputs found
Switchable Catalytic DNA Catenanes
Two-ring interlocked DNA catenanes
are synthesized and characterized. The supramolecular catenanes show
switchable cyclic catalytic properties. In one system, the catenane
structure is switched between a hemin/G-quadruplex catalytic structure
and a catalytically inactive state. In the second catenane structure
the catenane is switched between a catalytically active Mg<sup>2+</sup>-dependent DNAzyme-containing catenane and an inactive catenane state.
In the third system, the interlocked catenane structure is switched
between two distinct catalytic structures that include the Mg<sup>2+</sup>- and the Zn<sup>2+</sup>-dependent DNAzymes
Dual Switchable CRET-Induced Luminescence of CdSe/ZnS Quantum Dots (QDs) by the Hemin/G-Quadruplex-Bridged Aggregation and Deaggregation of Two-Sized QDs
The
hemin/G-quadruplex-catalyzed generation of chemiluminescence
through the oxidation of luminol by H<sub>2</sub>O<sub>2</sub> stimulates
the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS
quantum dots (QDs), resulting in the luminescence of the QDs. By the
cyclic K<sup>+</sup>-ion-induced formation of the hemin/G-quadruplex
linked to the QDs, and the separation of the G-quadruplex in the presence
of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence
of the QDs is demonstrated. QDs were modified with nucleic acids consisting
of the G-quadruplex subunits sequences and of programmed domains that
can be cross-linked through hybridization, using an auxiliary scaffold.
In the presence of K<sup>+</sup>-ions, the QDs aggregate through the
cooperative stabilization of K<sup>+</sup>-ion-stabilized G-quadruplex
bridges and duplex domains between the auxiliary scaffold and the
nucleic acids associated with the QDs. In the presence of 18-crown-6-ether,
the K<sup>+</sup>-ions are eliminated from the G-quadruplex units,
leading to the separation of the aggregated QDs. By the cyclic treatment
of the QDs with K<sup>+</sup>-ions/18-crown-6-ether, the reversible
aggregation/deaggregation of the QDs is demonstrated. The incorporation
of hemin into the K<sup>+</sup>-ion-stabilized G-quadruplex leads
to the ON-OFF switchable CRET-stimulated luminescence of the QDs.
By the mixing of appropriately modified two-sized QDs, emitting at
540 and 610 nm, the dual ON-OFF activation of the luminescence of
the QDs is demonstrated
Topoisomerase-Based Preparation and AFM Imaging of Multi-Interlocked Circular DNA
Multi-interlocked
circular DNA structures have been in high demand
for fabricating complicated functional DNA architectures and nanodevices
such as molecular switches, shuttles, and motors. Even though various
innovative methods have been developed in the past, creation of multi-interlocked
circular DNA structures with defined numbers of DNA molecules and
linking patterns is still a challenging task nowadays. Here, we propose
a top-down decatenation of kinetoplast DNA as a new approach for creating
multi-interlocked circular DNA structures. Through optimizing the
amount and reaction time of topoisomerase II, we synthesized completely
mutually interlocked tricircular, tetra-circular, and oligo-circular
DNA structures, which have not yet been acquirable through any other
existing synthetic means. The catenation structures of multiple circular
DNA were further verified through atomic force microscopic analysis
of the backbone overlapping patterns and the circumference. It accordingly
is our expectation that the top-down enzymatic approaches could offer
a highly interlocked network with defined numbers of circular DNA
with simple protocols, and could consequently be beneficial to the
design and fabrication of sophisticated functional molecules and nanodevices
in the areas of supramolecular chemistry, DNA nanotechnology, and
material science
Accelerating the Peroxidase-Like Activity of Gold Nanoclusters at Neutral pH for Colorimetric Detection of Heparin and Heparinase Activity
The
peroxidase-like catalytic activity of gold nanoclusters (Au-NCs)
is quite low around physiological pH, which greatly limits their biological
applications. Herein, we found heparin can greatly accelerate the
peroxidase-like activity of Au-NCs at neutral pH. The catalytic activity
of Au-NCs toward the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine
(TMB) oxidation by H<sub>2</sub>O<sub>2</sub> was 25-fold increased
in the presence of heparin at pH 7. The addition of heparin not only
accelerated the initial catalytic rate of Au-NCs but also prevented
the Au-NCs from catalyst deactivation. This allows the sensitive colorimetric
detection of heparin at neutral pH. In the presence of heparinase,
heparin was hydrolyzed into small fragments, weakening the enhancement
effect of catalytic activity. On the basis of this phenomenon, the
colorimetric determination of heparinase in the range from 0.1 to
3 μg·mL<sup>–1</sup> was developed with a detection
limit of 0.06 μg·mL<sup>–1</sup>. Finally, the detection
of heparin and heparinase activity in diluted serum samples was also
demonstrated
Accelerating the Phosphatase-like Activity of Uio-66-NH<sub>2</sub> by Catalytically Inactive Metal Ions and Its Application for Improved Fluorescence Detection of Cardiac Troponin I
Compared with natural enzymes, nanozymes
usually exhibit much lower
catalytic activities, which limit the sensitivities of nanozyme-based
immunoassays. Herein, several metal ions without enzyme-like activities
were engineered onto Uio-66-NH2 nanozyme through postsynthetic
modification. The obtained Mn+@Uio-66-NH2 (Mn+ = Zn2+, Cd2+, Co2+, Ca2+and Ni2+) exhibited
improved phosphatase-like catalytic activities. In particular, a 12-fold
increase in the catalytic efficiency (kcat/Km) of Uio-66-NH2 was observed
after the modification with Zn2+. Mechanism investigations
indicate that both the amino groups and oxygen-containing functional
groups in Uio-66-NH2 are the binding sites of Zn2+, and the modified Zn2+ ions on Uio-66-NH2 serve
as the additional catalytic sites for improving the catalytic performance.
Furthermore, the highly active Zn2+@Uio-66-NH2 was used as a nanozyme label to develop a fluorescence immunoassay
method for the detection of cardiac troponin I (cTnI). Compared with
pristine Uio-66-NH2, Zn2+@Uio-66-NH2 can widen the linear range by 1 order of magnitude (from 10 pg/mL–1
μg/mL to 1 pg/mL–1 μg/mL) and also lower the detection
limit by 5 times (from 4.7 pg/mL to 0.9 pg/mL)
“Light-on” Sensing of Antioxidants Using Gold Nanoclusters
Depletion
of intracellular antioxidants is linked to major cytotoxic
events and cellular disorders, such as oxidative stress and multiple
sclerosis. In addition to medical diagnosis, determining the concentration
of antioxidants in foodstuffs, food preservatives, and cosmetics has
proved to be very vital. Gold nanoclusters (Au-NCs) have a core size
below 2 nm and contain several metal atoms. They have interesting
photophysical properties, are readily functionalized, and are safe
to use in various biomedical applications. Herein, a simple and quantitative
spectroscopic method based on Au-NCs is developed to detect and image
antioxidants such as ascorbic acid. The sensing mechanism is based
on the fact that antioxidants can protect the fluorescence of Au-NCs
against quenching by highly reactive oxygen species. Our method shows
great accuracy when employed to detect the total antioxidant capacity
in commercial fruit juice. Moreover, confocal fluorescence microscopy
images of HeLa cells show that this approach can be successfully used
to image antioxidant levels in living cells. Finally, the potential
application of this “light-on” detection method in multiple
logic gate fabrication was discussed using the fluorescence intensity
of Au-NCs as output