NIR Plasmonic Nanozymes: Synergistic Enhancement Mechanism and Multi-Modal Anti-Infection Applications of MXene/MOFs.

Nanozymes are considered as the promising antimicrobial agents due to the enzyme-like activity for chemo-dynamic therapy (CDT). However, it remains a challenge to develop novel nanozyme systems for achieving stimuli-responsive, and efficient nanozyme catalysis with multimodal synergistic enhancement. In this work, a near-infrared (NIR) plasmonic-enhanced nanozyme catalysis and photothermal performance for effective antimicrobial applications are proposed. A Ti3 C2 MXene/Fe-MOFs composite (MXM) with NIR plasmonic-enhanced CDT combined with photothermal properties is successfully developed by loading metal-organic framework (MOF) nanozymes onto Ti3 C2 MXene. The mechanism of NIR induced localized surface plasmon resonance (LSPR)-enhanced CDT and photothermal therapy (PTT) is well explained through activation energy (Ea ), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), fluorescence analysis experiments, and finite element simulation. It reveals that MXene nanosheets exhibit NIR plasmon exciters and generate hot electrons that can transfer to the surface of Fe-MOFs, promoting the Fenton reaction and enhances CDT. While the photothermal heating of MXene produced by LSPR can also boost the CDT of Fe-MOFs under NIR irradiation. Both in vitro and in vivo experimental results demonstrate that LSPR-induced MXM system has outstanding antimicrobial properties, can promote angiogenesis and collagen deposition, leading to the accelerated wound healing.

Covalent Organic Framework Nanohydrogels.

Nanohydrogelation of covalent organic frameworks (COFs) will undoubtedly open up new applications for them in water, such as aqueous catalysis and biomedicine. It is currently a great challenge to achieve water dispersion of COFs through either bottom-up construction strategies or top-down exfoliating technologies. Herein, poly(N-isopropylacrylamide) (PNIPAM)-postmodified COF nanohydrogels (COF-NHGs) are successfully designed and synthesized via in situ atom-transfer radical polymerization (ATRP) on a scaffold of COFs. During the polymer growth process, the bulk COFs are exfoliated into nanosheets with a lateral size of ∼500 nm and a thickness of ∼6.5 nm. Moreover, their size can be precisely controlled by the degree of polymerization of PNIPAMs. In aqueous solution, the obtained COF-NHGs are assembled into nanohydrogels retaining intra-plane crystallinity and exhibit a temperature-sensitive sol-gel phase transition. With excellent solubility in organic solvents, the COF-NHGs' intrinsic physical properties in the solution state can be characterized through their solution nuclear magnetic resonance and ultraviolet absorption spectra. These results put forward new opportunities for regulating the solution processability of COFs and building an intelligent, stimuli-response platform of COF-polymer composite nanohydrogels for device applications.

MIL-101(CuFe) Nanozymes with Excellent Peroxidase-like Activity for Simple, Accurate, and Visual Naked-Eye Detection of SARS-CoV-2.

The COVID-19 pandemic has spread to every corner of the world and seriously affected our health and daily activities in the past three years; thereby, it is still urgent to develop various simple, quick, and accurate methods for early detection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. Nanozymes, a kind of nanomaterial with intrinsic enzyme-mimicking activity, have emerged as a suitable alternative for both therapy and diagnosis of SARS-CoV-2. Here, ultrasensitive and ultrafast MIL-101(CuFe)-CD147 biosensors are established for the detection of SARS-CoV-2 by a simple colorimetric method. A MIL-101(CuFe) metal-organic framework has excellent peroxidase-like activity due to the synergistic effect of Fe and Cu atoms. In addition, the MIL-101(CuFe)-CD147 biosensor shows great potential to detect the various variants of SARS-CoV-2 due to the universal receptor of CD147. The enzyme-based biosensor for the detection of SARS-CoV-2 achieves a very low limit of detection (about 3 PFU/mL) within 30 min. Therefore, the present method provides a new generation of an alternative approach for highly sensitive and visual diagnosis of COVID-19.

Full-Color-Tunable Nanohydrogels as High-Stability Intracellular Nanothermometers.

Full-color-tunable hydrogels with ultrahigh stability can be used in various fields, including intracellular temperature sensing. However, constructing full-color-tunable organic nanohydrogels with excellent biocompatibility and stability for intracellular temperature sensing remains a great challenge. Here, we report a full-color-tunable nanohydrogel with ultrahigh stability as an intracellular nanothermometer. Three types of temperature-sensitive polymers with red, green, and blue fluorescence were synthesized. Through easy mixing of these three polymers with regulation of the mass ratio, these polymers can be encoded to full-color-tunable fluorescent nanohydrogels, including nanohydrogels with white-light emission (NWLEs), with sizes of about 200 nm in aqueous media. Further study suggested that the as-obtained NWLEs exhibited good performance in intracellular temperature sensing because of their ultrahigh stability on their fluorescence properties and morphologies.

A Dual-Mode NADH Biosensor Based on Gold Nanostars Decorated CoFe2 Metal-Organic Frameworks to Reveal Dynamics of Cell Metabolism.

Nicotinamide adenine dinucleotide (NADH) is central to metabolism and implicated in various diseases. Herein, nanohybrids of gold nanostars and metal-organic frameworks are devised and demonstrated as a dual-mode NADH sensor, for which colorimetric detection is enabled by its peroxidase-like nanozyme property and Raman detection is realized by its surface-enhanced Raman scattering property with the detection limit as low as 28 pM. More importantly, this probe enables real-time SERS monitoring in living cells, providing a unique tool to investigate dynamic cellular processes involving NADH. Our experiments reveal that metabolism dynamics is accelerated by glucose and is much higher in cancerous cells. The SERS results can also be verified by the colorimetric detection. This sensor provides a new potential to detect biomarkers and their dynamics in situ.

Gold Nanorods/Metal-Organic Framework Hybrids: Photo-Enhanced Peroxidase-Like Activity and SERS Performance for Organic Dyestuff Degradation and Detection.

Metal-organic frameworks (MOFs) are widely used to mimic enzymes for catalyzing chemical reactions; however, low enzyme activity limit their large-scale application. In this work, gold nanorods/metal-organic frameworks (Au NRs/Fe-MOF) hybrids were successfully synthesized for photo-enhanced peroxidase-like catalysis and surface-enhanced Raman spectroscopy (SERS). The enzyme-like activity of Au NRs/Fe-MOF hybrids was significantly enhanced under localized surface plasmon resonance (LSPR), because the hot electrons produced on Au NRs surface were transferred into Fe-MOF, activating the Fenton reaction by Fe3+/Fe2+ conversion and preventing the recombination of hot electrons and holes. This photo-enhanced enzyme-like catalytic performance was investigated by X-ray photoelectron spectrometry (XPS), electrochemical analysis, activation energy measurement, and in situ Raman spectroscopy. Afterward, Methylene Blue (MB) was chosen to demonstrate the photo-enhanced peroxidase-like performance of Au NRs/Fe-MOFs. The Au NRs/Fe-MOF caused chemical and electromagnetic enhancement of Raman signals and exhibited a great potential for the detection of toxic chemicals and biological molecules. The detection limit of MB concentration is 9.3 × 10-12 M. In addition, the Au NRs/Fe-MOF hybrids also showed excellent stability and reproducibility for photo-enhanced peroxidase-like catalysis. These results show that nanohybrids have great potential in many fields, such as sensing, cancer therapy, and energy harvesting.