Photocatalytic methane conversion requires a strong polarization environment composed of abundant activation sites with the robust stretching ability for C-H scissoring. High-density frustrated Lewis pairs consisting of low-valence Lewis acid Nb and Lewis base Nb-OH are fabricated on lamellar Nb2O5 through a thermal-reduction promoted phase-transition process. Benefitting from the planar atomic arrangement of lamellar Nb2O5, the frustrated Lewis pairs sites are highly exposed and accessible to reactants, which results in a superior methane conversion rate of 1456 μmol g−1 h−1 for photocatalytic non-oxidative methane coupling without the assistance of noble metals. The time-dependent DFT calculation demonstrates the photo-induced electron transfer from LA to LB sites enhances their intensities in a concerted way, promoting the C-H cleavage through the coupling of LA and LB. This work provides in-depth insight into designing and constructing a polarization micro-environment for photocatalytic C-H activation of methane without the assistance of noble metals.
Herein,
a hierarchically porous Zr-MOF-labeled electrochemical
aptasensor based on the composite of PtPd@Ni-Co hollow nanoboxes (PtPd@Ni-Co
HNBs) and poly (diallyldimethylammonium chloride)-functionalized graphene
(PDDA-Gr) was developed for ultrasensitive detection of chloramphenicol
(CAP). PtPd@Ni-Co HNBs have excellent conductivity and provide binding
sites for aptamers; the functionalized PDDA-Gr improves its dispersibility
and conductivity as a substrate material, which can be successfully
used to increase the electrode surface area and support more PtPd@Ni-CoHNBs.
Besides, hierarchically porous Zr-MOFs (HP-UiO-66) were utilized as
signal probes and showed a stronger load capacity for signal molecules
than conventional UiO-66. In the presence of CAP, two ingeniously
designed Exo III-assisted cyclic amplification strategies further
improved the sensitivity of the aptasensor: CAP causes cycle I to
release a large amount of trigger DNA (Tr DNA), and then, Tr DNA initiated
cycle II, which causes the exposed capture DNA to further bind the
signal probes. With these advantages, the constructed aptasensors
performed with satisfactory sensitivity in a wide linear range (10
fM–10 nM) and a detection limit of 0.985 fM. Several signal
amplification strategies adopted in this study have effectively improved
the performance of the sensor, providing a new avenue for the development
of ultrasensitive sensors in the food analysis field.
The
abuse of chloramphenicol (CAP) in animal-derived products leads
to serious food safety problems, so the sensitive and accurate determination
of CAP residues has great noteworthiness for public health. Herein,
we present a novel electrochemical aptasensor that incorporates a
poly(diallyldimethylammonium chloride) functionalized graphene/Ag@Au
nanosheets (PDDA-Gr/Ag@Au NSs) composite modified electrode and a
DNAzyme signal amplification effect triggered by a triple-helix molecular
switch (THMS) for detecting CAP. The PDDA-Gr/Ag@Au NSs composite has
the advantages of high surface area, great conductivity, and dispersibility
and has successfully improved the electrochemical performance of the
electrode. Specific interaction with CAP will cause the signal transduction
probe (STP) to be released from the THMS. After that, the DNAzyme
will be activated with the help of Pb2+ and remove the
immobilized signal probe on the electrode surface. The signal change
was recorded by square wave voltammetry (SWV) and led to an accurate
quantification of CAP. With all these features, the proposed sensing
strategy yielded a satisfactory analytical performance with linearity
between 1 pM and 1 μM and a limit of detection of 18.6 fM. Furthermore,
the aptasensor shows excellent specificity for CAP in the presence
of other antibiotics and resists interference with other common metal
ions. Importantly, the performance is not diminished when the constructed
aptasensor is applied to measuring CAP in milk powder. This THMS-based
method is easy to design, and alteration to different targets can
be achieved by simply replacing the aptamer sequence in the THMS.
Therefore, this method shows significant prospects as a flexible platform
for accurate monitoring of antibiotic residues in foodstuffs.
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