Biomimic nanozymes coassembled by
peptides or proteins and small
active molecules provide an effective strategy to design attractive
nanozymes. Although some promising nanozymes have been reported, rational
regulation for higher catalytic activity of biomimic nanozymes remains
challenging. Hence, we proposed a novel biomimic nanozyme by encapsulating
the coassembly of hemin/bovine serum albumin (BSA) in zeolite imidazolate
frameworks (ZIF-8) to achieve controllable tailoring of peroxidase-like
activity via the confinement effect. The assembly of Hemin@BSA was
inspired by the structure of horseradish peroxidase (HRP), in which
hemin served as the active cofactor surrounded by BSA as a blocking
pocket to construct a favorable hydrophobic space for substrate enrichment.
Benefiting from the confinement effect, ZIF-8 with a porous intracavity
was identified as the ideal outer layer for Hemin@BSA to accelerate
substrate transport and achieve internal circulation of peroxidase-like
catalysis, significantly enhancing its peroxidase-like activity. Especially,
the precise encapsulation of Hemin@BSA in ZIF-8 could also prevent
it from decomposition in harsh environments by rapid crystallization
around Hemin@BSA to form a protective shell. Based on the improved
peroxidase-like activity of Hemin@BSA@ZIF-8, several applications
were successfully performed for the sensitive detection of small molecules
including H2O2, glucose, and bisphenol A (BPA).
Satisfactory results highlight that using a ZIF-8 outer layer to encapsulate
Hemin@BSA offers a very effective and successful strategy to improve
the peroxidase-like activity and the stability of biomimic nanozymes,
broadening the potential application of biocatalytic metal–organic
frameworks (MOFs).
The necessary step of directly adding hydrogen peroxide
(H2O2) into the detection system in traditional
immunoassays
hampers their applications as a portable device for point-of-care
analysis due to the unstable liquid form of H2O2. Herein, a strategy of self-supplying H2O2 and signal amplification triggering by copper peroxide nanodots
encapsulated (CPNs) in metal–organic frameworks (ZIF-8) was
proposed in an immunoassay for dual-signal detection of bisphenol
A (a typical emerging organic pollutant), which was further fabricated
as a lab-in-a-tube device integrated with a smartphone sensing platform.
Herein, CPNs@ZIF-8 was modified on the antibody against bisphenol
A; after the competitive binding of analytes, coating antigens, and
antibodies, the released H2O2 and Cu2+ from encapsulated CPNs under the acidic condition will trigger a
Fenton-like reaction to generate ·OH for oxidization of TMB;
meanwhile, Cu2+ could quench the fluorescence of GSH-Au
NCs, resulting in dual-mode signals for measurements. Most importantly,
self-supplying H2O2 with high stability was
undertaken by CPNs, and the remarkably increased signal molecule (CPN)
loading was ascribed to the excellent capacity of metal–organic
frameworks (ZIF-8). In addition, good recoveries were obtained from
a colorimetric/fluorescent dual-mode strategy. The constructed device
demonstrated great potential as a universal platform for rapid detection
of various environmental contaminants using corresponding antibodies
relying on its performance of satisfactory stability, sensitivity,
and accuracy.
Adsorption
of DNA probes onto nanomaterials is a promising strategy
for bioassay establishment typically using fluorescence or catalytic
activities to generate signals. Albeit important, there is currently
a lack of systematic understanding of the sensing behaviors building
on nanomaterial–DNA interactions, which greatly limits the
rational method design and their subsequent applications. Herein,
the issue was investigated by employing multifunctional metal–organic
frameworks (MOFs) (FeTCPP⊂UiO-66) as a model that was synthesized
via integrating heme-like ligand FeTCPP into commonly used MOFs (UiO-66).
Our results demonstrated that the fluorescently labeled DNA adsorbed
onto FeTCPP⊂UiO-66 was quenched through photoinduced electron
transfer, fluorescence resonance energy transfer, and the internal
filtration effect. Among different DNA structures, double-stranded
DNA and hybridization chain reaction products largely retained their
fluorescence due to desorption and conformational variation, respectively.
In addition, ssDNA could maximally inhibit the peroxidase activity
of FeTCPP⊂UiO-66, and this inhibition was strongly dependent
on the strand length but independent of base composition. On the basis
of these discoveries, a fluorescence/colorimetric dual-modal detection
was designed against aflatoxin B1 with satisfactory performances obtained
to further verify our results. This study provided some new insights
into the sensing behaviors based on MOF–DNA interactions, indicating
promising applications for rational bioassay design and its performance
improvement.
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