Optimizing oxygen vacancies through grain boundary engineering to enhance electrocatalytic nitrogen reduction.

Electrocatalytic nitrogen reduction is a challenging process that requires achieving high ammonia yield rate and reasonable faradaic efficiency. To address this issue, this study developed a catalyst by in situ anchoring interfacial intergrown ultrafine MoO2 nanograins on N-doped carbon fibers. By optimizing the thermal treatment conditions, an abundant number of grain boundaries were generated between MoO2 nanograins, which led to an increased fraction of oxygen vacancies. This, in turn, improved the transfer of electrons, resulting in the creation of highly active reactive sites and efficient nitrogen trapping. The resulting optimal catalyst, MoO2/C700, outperformed commercial MoO2 and state-of-the-art N2 reduction catalysts, with NH3 yield and Faradic efficiency of 173.7 µg h-1 mg-1cat and 27.6%, respectively, under - 0.7 V vs. RHE in 1 M KOH electrolyte. In situ X-ray photoelectron spectroscopy characterization and density functional theory calculation validated the electronic structure effect and advantage of N2 adsorption over oxygen vacancy, revealing the dominant interplay of N2 and oxygen vacancy and generating electronic transfer between nitrogen and Mo(IV). The study also unveiled the origin of improved activity by correlating with the interfacial effect, demonstrating the big potential for practical N2 reduction applications as the obtained optimal catalyst exhibited appreciable catalytic stability during 60 h of continuous electrolysis. This work demonstrates the feasibility of enhancing electrocatalytic nitrogen reduction by engineering grain boundaries to promote oxygen vacancies, offering a promising avenue for efficient and sustainable ammonia production.

Biomimetic Mineralization Synthesis of Flower-Like Cobalt Selenide/Reduced Graphene Oxide for Improved Electrochemical Deionization.

Rationally and precisely tuning the composition and structure of materials is a viable strategy to improve electrochemical deionization (EDI) performances, which yet faces enormous challenges. Herein, an eco-friendly biomimetic mineralization synthetic strategy is developed to synthesize the flower-like cobalt selenide/reduced graphene oxide (Bio-CoSe2 /rGO) composites and used as advanced sodium ion adsorption electrodes. Benefiting from the slow and controllable reaction kinetics provided by the biomimetic mineralization process, the flower-like CoSe2 is uniformly constructed in the rGO, which is endowed with robust architecture, substantial adsorption sites and rapid charge/ion transport. The Bio-CoSe2 /rGO electrode yields the maximum salt adsorption capacity and salt adsorption rate of 56.3 mg g-1 and 5.6 mg g-1 min-1 respectively, and 92.5% capacity retention after 60 cycles. These results overmatch the pristine CoSe2 and irregular granular CoSe2 /rGO synthesized by a hydrothermal method, proving the structural superiority of the Bio-CoSe2 /rGO composites. Furthermore, the in-depth adsorption kinetics study indicates the chemisorption nature of sodium ion adsorption. The structures of the Bio-CoSe2 /rGO composites after long term EDI cycles are intensively studied to unveil the mechanism behind such superior EDI performances. This study offers one effective method for constructing advanced EDI electrodes, and enriches the application of the biomimetic mineralization synthetic strategy.

Support Platform of Functionalized Sustainable Cellulose Self-Entanglement Monolithic Adsorbents for Efficient Adsorption of Cadmium(II) Ions.

Serious water contamination induced by massive discharge of cadmium(II) ions is becoming an emergent environmental issue due to high toxicity and bioaccumulation; thus, it is extremely urgent to develop functional materials for effectively treating with Cd2+ from wastewater. Benefiting from abundant binding sites, simple preparation process, and adjustable structure, UiO-66-type metal-organic frameworks (MOFs) had emerged as promising candidates in heavy metal adsorption. Herein, monolithic UiO-66-(COOH)2-functionalized cellulose fiber (UCLF) adsorbents were simply fabricated by incorporating MOFs into cellulose membranes through physical blending and self-entanglement. A two-dimensional structure was facilely constructed by cellulose fibers from sustainable biomass agricultural waste, providing a support platform for the integration of eco-friendly UiO-66-(COOH)2 synthesized with lower temperature and toxicity solvent. Structure characterization and bath experiments were performed to determine operational conditions for the maximization of adsorption capacity, thereby bringing out an excellent adsorption capacity of 96.10 mg/g. UCLF adsorbent holding 10 wt % loadings of UiO-66-(COOH)2 (UCLF-2) exhibited higher adsorption capacity toward Cd2+ as compared to other related adsorbents. Based on kinetics, isotherms, and thermodynamics, the adsorption behavior was spontaneous, exothermic, as well as monolayer chemisorption. Coordination and electrostatic attraction were perhaps mechanisms involved in the adsorption process, deeply unveiled by the effects of adsorbate solution pH and X-ray photoelectron spectroscopy. Moreover, UCLF-2 adsorbent with good mechanical strength offered a structural guarantee for the successful implementation of practical applications. This study manifested the feasibility of UCLF adsorbents used for Cd2+ adsorption and unveiled a novel strategy to shape MOF materials for wastewater decontamination.

Amorphous Fe-Containing Phosphotungstates Featuring Efficient Peroxidase-like Activity at Neutral pH: Toward Portable Swabs for Pesticide Detection with Tandem Catalytic Amplification.

Peroxidase-mimetic materials are intensively applied to establish multienzyme systems because of their attractive merits. However, almost all of the nanozymes explored exhibit catalytic capacity only under acidic conditions. The pH mismatch between peroxidase mimics in acidic environments and bioenzymes under neutral conditions significantly restricts the development of enzyme-nanozyme catalytic systems especially for biochemical sensing. To solve this problem, here amorphous Fe-containing phosphotungstates (Fe-PTs) featuring high peroxidase activity at neutral pH were explored to fabricate portable multienzyme biosensors for pesticide detection. The strong attraction of negatively charged Fe-PTs to positively charged substrates as well as the accelerated regeneration of Fe2+ by the Fe/W bimetallic redox couples was demonstrated to play important roles in endowing the material with peroxidase-like activity in physiological environments. Consequently, integrating the developed Fe-PTs with acetylcholinesterase and choline oxidase led to an enzyme-nanozyme tandem platform with good catalytic efficiency at neutral pH for organophosphorus pesticide response. Furthermore, they were immobilized onto common medical swabs to fabricate portable sensors for paraoxon detection conveniently based on smartphone sensing, showing excellent sensitivity, good anti-interference capacity, and low detection limit (0.28 ng/mL). Our contribution expands the horizon of acquiring peroxidase activity at neutral pH, and it will also open avenues to construct portable and effective biosensors for pesticides and other analytes.

MnOx In Situ Growth-Induced Luminescence and Oxidase-Like Feature Bimodulation of CePO4:Tb Nanorods: Toward Ascorbic Acid-Related Bioanalysis in a "One-Stone-Two-Birds" Manner.

Nanozyme-based multimode detection is a useful means to improve the accuracy and stability of analytical methods. However, both multifunctional nanozymes and related multimodal sensing strategies are still very scarce. Besides, they require complex processes to fabricate and operate. To fill this gap, here we propose a spontaneous interfacial in situ growth strategy to prepare a new bifunctional material (CePO4:Tb@MnOx) featuring good oxidase-like activity and green photoluminescence for the dual-mode colorimetric/luminescence determination of ascorbic acid (AA)-related biomarkers specifically. CePO4:Tb@MnOx was gained through the controllable redox reaction between KMnO4 and CePO4:Tb nanorods. It was interestingly found that MnOx in situ growth not only significantly enhanced the enzyme-like activity but also could reversibly regulate the luminescence of CePO4:Tb via a dual quenching mechanism. More interestingly, CePO4:Tb@MnOx exhibited a distinctive response toward AA against other reducing species. A double-coordination regulation mechanism was further verified to clarify the catalytic activity and luminescence switching behaviors in CePO4:Tb@MnOx. Based on these findings, a dual-mode colorimetric/luminescence approach was established for AA sensing in a "one-stone-two-birds" manner, providing excellent selectivity, sensitivity, and practicability. Furthermore, the determination of AA-related biomarkers, including acid phosphatase activity and organophosphorus residue, was also validated by the sensing principle. Our work not only deepens the understanding of the coordinated regulation of the luminescence and enzyme-like features in lanthanide-based materials but also offers a novel way to design and develop multifunctional nanozymes for advanced bioanalytical applications.

Oxygen Vacancy-Induced Metal-Support Interactions in AuPd/ZrO2 Catalysts for Boosting 5-Hydroxymethylfurfural Oxidation.

The construction of strong metal-support interactions in oxide-supported noble metal nanocatalysts has been considered an emerging and efficient way in improving catalytic performance in biomass-upgrading reactions. Herein, a citric acid (CA)-assisted synthesized ZrO2 layer with improved oxygen vacancy (Ov) concentrations on a natural clay mineral of halloysite nanotubes (HNTs) was designed. Moreover, AuxPdy/ZrO2@HNTs-zCA catalysts were prepared by loading AuPd bimetal and employed for aerobic oxidation of the lignocellulosic biomass-derived 5-hydroxymethylfurfural (HMF) platform to the bioplastic monomer 2,5-furandicarboxylic acid (FDCA) with water as the solvent. The results of catalytic experiments revealed that the Au3Pd1/ZrO2@HNTs-1.0CA catalyst exhibited excellent catalytic activity at 0.5 MPa O2, with a satisfactory FDCA yield of 99.5% and outstanding FDCA formation rate of 1057.9 mmol·g-1·h-1. The improved Ov concentration in the ZrO2 support enhanced the adsorption and activation ability of the catalyst for O2, and a higher Lewis acid concentration provided a stronger adsorption ability of the catalyst for reaction substrates. Besides, the synergistic effect of AuPd bimetallic nanoparticles steered the tandem oxidation of aldehyde and alcohol groups in HMF and accelerated the rate-determining step. More importantly, the relationship between the Ov concentration and catalytic performance also demonstrated that the enhanced catalytic activity for HMF oxidation was mainly attributed to the active interface of AuPd-ZrOx. This work offers fresh insights into rationally designing oxygen vacancy-driven strong interactions between the oxide support and noble nanoparticles for the catalytic upgrade of biomass platform chemicals.

Fine mapping of genes controlling pigment accumulation in oilseed rape (Brassica napus L.).

Purple/red appearance is one of the common phenotypic variations in leaves, stems, and siliques of oilseed rape (Brassica napus L.) but very rare in flowers. In this study, the causal genes for the purple/red traits in stems and flowers in two accessions of oilseed rape (DH_PR and DH_GC001, respectively) derived from the wide hybridization were fine mapped, and candidate genes were determined by methods combined with bulked segregant analysis (BSA) and RNA-seq analysis. Both traits of purple stem and red flowers were mapped to the locus as AtPAP2 homologous genes (BnaPAP2.C6a and BnaPAP2.A7b, respectively) belonging to the R2R3-MYB family. Sequence comparisons of full-length allelic genes revealed several InDels and SNPs in intron 1 as well as exons, and completely different promoter region of BnaPAP2.C6a and a 211 bp insertion was identified in the promoter region of BnaPAP2.A7b of DH_GC001. Our results not only contribute to a better understanding of anthocyanin inheritance in B. napus, but also provide a useful toolbox for future breeding of cultivars with purple/red traits through the combination of different functional alleles and homologs. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01365-5.

Modulating photothermal properties by integration of fined Fe-Co in confined carbon layer of SiO2 nanosphere for pollutant degradation and solar water evaporation.

Environmental governance by photothermal materials especially for the separation of organic pollutants and regeneration of freshwater afford growing attention owing to their special solar-to-heat properties. Here, we construct a special functional nanosphere composed of an internal silica core coated by a thin carbon layer encapsulated plasmonic bimetallic FeCo2O4 spinel (SiO2@CoFe/C) by a facile self-assembled approach and tuned calcination. Through combining the advantage of bimetallic Fe-Co and carbon layer, this obtained nanosphere affords improved multiple environmental governing functions including peroxymonosulfate (PMS) activation to degrade pollutants and photothermal interfacial solar water evaporation. Impressively, fined bimetal (FeCo) species (20 nm) acted as main catalytic substance were distributed on the N-doping carbon thin layer, which favors electron transfer and reactive accessibility of active metals. The increasing treatment temperature of catalysts caused the optimization of the surface active metal species and tuning catalytic properties in the AOPs. Besides, the incorporation of Co in the SiO2@CoFe/C-700 could enable the improved PMS activation efficiency compared to SiO2@Fe/C-700 and the mixed SiO2@Co/C-700 and SiO2@Fe/C-700, hinting a synergetic promotion effect. The bimetal coupled catalyst SiO2@CoFe/C-700 affords enhanced photothermal properties compared to SiO2@Co/C-700. Furthermore, photothermal catalytic PMS activation using optimal SiO2@CoFe/C-700 was further explored in addressing stubborn pollutants including oxytetracycline, sulfamethoxazole, 2, 4-dichlorophenol, and phenol. The free radical quenching control suggests that both the sulfate radical, hydroxyl radical, superoxide radical, and singlet oxygen species are involved in the degradation, while the hydroxyl radical and singlet oxygen play a dominant role. Furthermore, the implementation of a solar-driven interfacial water evaporation model using SiO2@CoFe/C-700 was further studied to obtain freshwater regeneration (1.26 kg m-2 h-1, 76.81% efficiency), indicating the comprehensive ability of the constructed nanocomposites for treating complicated environmental pollution including organics removal and freshwater regeneration.

Nucleoside Analogs: A Review of Its Source and Separation Processes.

Nucleoside analogs play a crucial role in the production of high-value antitumor and antimicrobial drugs. Currently, nucleoside analogs are mainly obtained through nucleic acid degradation, chemical synthesis, and biotransformation. However, these methods face several challenges, such as low concentration of the main product, the presence of complex matrices, and the generation of numerous by-products that significantly limit the development of new drugs and their pharmacological studies. Therefore, this work aims to summarize the universal separation methods of nucleoside analogs, including crystallization, high-performance liquid chromatography (HPLC), column chromatography, solvent extraction, and adsorption. The review also explores the application of molecular imprinting techniques (MITs) in enhancing the identification of the separation process. It compares existing studies reported on adsorbents of molecularly imprinted polymers (MIPs) for the separation of nucleoside analogs. The development of new methods for selective separation and purification of nucleosides is vital to improving the efficiency and quality of nucleoside production. It enables us to obtain nucleoside products that are essential for the development of antitumor and antiviral drugs. Additionally, these methods possess immense potential in the prevention and control of serious diseases, offering significant economic, social, and scientific benefits to the fields of environment, biomedical research, and clinical therapeutics.

Facile Synthesis of Asymmetric aza-Boron Dipyrromethene Analogues Bearing Quinoxaline Moiety.

An asymmetric aza-BODIPY analogue bearing quinoxaline moiety was synthesized via a titanium tetrachloride-mediated Schiff-base-forming reaction of 6,7-dimethyl-1,4-dihydroquinoxaline-2,3-dione and benzo[d]thiazol-2-amine. This novel aza-BODIPY analogue forms a complementary hydrogen-bonded dimer due to the quinoxaline moiety in the crystal structure. It also shows intense absorption and fluorescence, with fluorescence quantum yields close to unity. The electrochemical measurements and the DFT calculations revealed the presence of the low-lying HOMO, which benefits their potential applications as an electron-transporting material.

Near-Infrared Photoacoustic Probe for Reversible Imaging of the ClO-/GSH Redox Cycle In Vivo.

Homeostasis of the cellular redox status plays an indispensable role in diverse physiological and pathological processes. Hypochlorite anion (ClO-) and glutathione (GSH) represent an important redox couple to reflect the redox status in living cells. The current cellular redox probes that detect either ClO- or GSH alone are not accurate enough to monitor the real redox status. In this work, a reversible photoacoustic (PA) probe, DiOH-BDP, has been synthesized and applied for PA imaging to monitor the ClO-/GSH couple redox state in an acute liver injury (ALI) model. The near-infrared PA probe DiOH-BDP features significant changes in absorption between 648 and 795 nm during the selective oxidation by ClO- and the reductive recovery of GSH, which exhibits excellent selectivity and sensitivity toward ClO- and GSH with the limits of detection of 77.7 nM and 7.2 µM, respectively. Additionally, using PA770 as a detection signal allows for the in situ monitoring of the ClO-/GSH couple, which realizes mapping of the localized redox status of the ALI by the virtue of a PA imaging system. Therefore, the probe provides a potentially technical tool to understand redox imbalance-related pathological formation processes.

Synthesis, Characterization, and Electrochemistry of Copper Dibenzoporphyrin(2.1.2.1) Complexes.

Three copper dibenzoporphyrin(2.1.2.1) complexes having two dipyrromethene units connected through o-phenylen bridges and 4-MePh, Ph, or F5Ph substituents at the meso positions of the dipyrrins were synthesized and characterized according to their spectral, electrochemical, and structural properties. As indicated by the single-crystal X-ray structures, all three derivatives have highly bent molecular structures, with angles between each planar dipyrrin unit ranging from 89° to 85°, indicative of a nonaromatic molecule. The insertion of copper(II) into dibenzoporphyrins(2.1.2.1) induced a change in the macrocyclic cavity shape from rectangular in the case of the free-base precursors to approximately square for the metalated copper derivatives. Solution electron paramagnetic resonance (EPR) spectra at 100 K showed hyperfine coupling of the Cu(II) central metal ion and the N nucleus in the highly bent molecular structures. Electrochemical measurements in CH2Cl2 or N,N-dimethylformamide (DMF) containing 0.1 M tetrabutylammonium perchlorate (TBAP) were consistent with ring-centered electron transfers and, in the case of reduction, were assigned to electron additions involving two equivalent π centers on the bent nonaromatic molecule. The potential separation between the two reversible one-electron reductions ranged from 230 to 400 mV in DMF, indicating a moderate-to-strong interaction between the equivalent redox-active dipyrrin units of the dibenzoporphyrins(2.1.2.1). The experimentally measured highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps ranged from 2.14 to 2.04 eV and were smaller than those seen for the planar copper tetraarylporphyrins(1.1.1.1), (Ar)4PCu.

Composite Hydrogel Microspheres Encapsulating Hollow Mesoporous Imprinted Nanoparticles for Selective Capture and Separation of 2'-Deoxyadenosine.

Hollow mesoporous silica nanoparticles have been widely applied as a carrier material in the molecular imprinting process because of their excellent properties, with high specific surface area and well-defined active centers. However, these kinds of materials face the inevitable problem that they have low mass transfer efficiency and cannot be conveniently recycled. In order to solve this problem, this work has developed a composite hydrogel microsphere (MMHSG) encapsulated with hollow mesoporous imprinted nanoparticles for the selective extraction of 2'-deoxyadenosine (dA). Subsequently, the hollow mesoporous imprinted polymers using dA as template molecule and synthesized 5-(2-carbomethoxyvinyl)-2'-deoxyuridine (AcrU) as functional monomer were encapsulated in hydrogel. MMHSG displayed good performance in specifically recognizing and quickly separating dA, whereas no imprinting effect was observed among 2'-deoxyguanosine (dG), deoxycytidine (dC), or 5'-monophosphate disodium salt (AMP). Moreover, the adsorption of dA by MMHSG followed chemisorption and could reach adsorption equilibrium within 60 min; the saturation adsorption capacity was 20.22 µmol·g-1. The introduction of AcrU could improve selectivity through base complementary pairing to greatly increase the imprinting factor to 3.79. Therefore, this was a successful attempt to combine a hydrogel with hollow mesoporous silica nanoparticles and molecularly imprinted material.

Dynamic Synthetic Biointerfaces: From Reversible Chemical Interactions to Tunable Biological Effects.

Dynamic synthetic biointerface is a new concept of biomaterials with smart surface properties capable of controlled display of bioactive ligands, dynamic modulation of cell-biomaterial interactions, and subsequently clever manipulation of fundamental cell behaviors like adhesion, migration, proliferation, differentiation, apoptosis, and so on. As mimics of the extracellular matrix (ECM), such molecularly dynamic biointerfaces have attracted increasing attention because of their tunable biological effects with great significance in in situ cell biology, tissue engineering, drug targeting, and cell isolation for cancer theranostics. Approaches to control bioligand presentation on materials mainly rely on surface functionalization with dynamic or reversible chemical linkers to which the ligands are tethered. Photoelectric-transformable or photocleavable chemistry, host-guest supramolecular chemistry, and multiple noncovalent interactions were initially employed for fabrication of dynamic synthetic biointerfaces. However, the external stimuli required in these systems, including electrochemical potential, electrochemical reaction, and near-infrared or UV light, are mostly invasive to living cells; and few of them are able to respond to the stimuli occurring in natural biological processes. In addition, most of current systems focused only on the control of cell adhesion, other cell behaviors like migration, differentiation and apoptosis have rarely been explored. Therefore, the development of novel synthetic biointerfaces that permit access to noninvasive control of diverse cell behaviors still represents a key challenge in biomaterials science. Our group pioneers the use of reversible covalent bonds, metal coordinative interactions, and the molecular affinity of molecularly imprinted synthetic receptors as the dynamic driving forces for the fabrication of smart biointerfaces. Several typical biological stimuli, such as glycemic volatility, body temperature fluctuations, regional disparity of pH values, and specific biomolecules, were tactfully involved in our systems. In this Account, we highlight the strategies we have used on the exploitation of dynamic synthetic biointerfaces based on the above three types of reversible chemical interactions. While our attention has been focused on biologically stimuli-responsive or other noninvasive ligand presentation, the versatility of dynamic synthetic biointerfaces in control of cell adhesion, directing cell differentiation, and targeting cell apoptosis has also been successfully demonstrated. In addition, a paradigm shift of dynamic synthetic biointerfaces from macroscopic to microscopic scale (e.g., nanobiointerfaces) was conceptually demonstrated in our research. The potential applications of these developed dynamic systems, including fundamental cell biology, surface engineering of biomaterials, scaffold-free tissue engineering, cell-based cancer diagnosis, and drug targeting cancer therapy, were also introduced, respectively. Although the development of dynamic synthetic biointerfaces is still in its infancy, we strongly believe that further efforts in this field will play a continuously and increasingly significant role in bridging the gap between chemistry and biology.

Smartphone-assisted off─on photometric determination of phosphate ion based on target-promoted peroxidase-mimetic activity of porous CexZr1-xO2 (x≥0.5) nanocomposites.

Given the level of phosphate ion (Pi) is a significant indicator of eutrophication in environmental waters, it becomes quite important to develop efficient methods for its monitoring. In this research, we developed a smartphone-assisted off─on photometric approach for Pi analysis based on the analyte-promoted peroxidase-mimicking catalytic activity of porous CexZr1-xO2 (x ≥ 0.5) nanocomposites. The Ce4+/Ce3+ redox pair in CexZr1-xO2 endowed it with certain activity to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) color reaction with the participation of H2O2, and both the existing Zr4+ and Ce4+ species enabled the nanozyme to specifically recognize Pi. It was observed that the bonded Pi could greatly promote the peroxidase-like activity of the CexZr1-xO2 nanocomposite towards positively charged TMB. According to the new finding, high-performance sensing of Pi with wide detection range, high sensitivity and good selectivity was realized, giving a detection limit down to 0.09 µM. Further, a 3D-printed smartphone-based signal reading system was designed and coupled with the sensing method, enabling the rapid, convenient, in-field and instrument-free analysis of Pi for environmental monitoring.

Enzyme-triggered in situ formation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity.

Given that alkaline phosphatase (ALP) is an important biomarker for many diseases, monitoring of its activity turns to be of great significance for related disease diagnosis and treatment. Herein, we report a new colorimetric assay based on the enzyme-triggered in situ formation of Ag nanoparticles (NPs) with high oxidase-mimicking activity for ALP activity detection. ALP first hydrolyzes the ascorbic acid phosphate (AAP) substrate to produce ascorbic acid (AA); the produced AA with strong reducing capacity then transforms Ag+ into Ag NPs; compared with the Ag+ precursor, the in situ formed Ag NPs have much higher oxidase-like activity to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) color reaction mediated by dissolved O2 at neutral pH. On the basis of this principle, amplified colorimetric detection of ALP activity with a linear scope of 0.15-5 U L-1 and a limit of detection down to 0.037 U L-1 was realized. In addition, our assay exhibited specific response toward ALP against other biological enzymes and species. Accurate and reliable determination of ALP activity in human plasma was also demonstrated by our assay, suggesting its great potential as a facile and efficient tool for monitoring of ALP activity in clinical practice.

Colorimetric determination of As(III) based on 3-mercaptopropionic acid assisted active site and interlayer channel dual-masking of Fe-Co-layered double hydroxides with oxidase-like activity.

A colorimetric method is described for the determination of As(III). It is based on the use of 3-mercaptopropionic acid (3-MPA) assisted active site and interlayer channel dual-masking of oxidase-like Fe-Co-layered double hydroxides (Fe-Co-LDH). The Fe-Co-LDH acts as an oxidase-mimicking nanozyme with high activity. It catalyzes the oxidation of colorless 3,3'5,5'-tetramethylbenzidine (TMB) to form a blue product (oxTMB) with an absorption maximum at 652 nm. It is found that As(III) firmly anchors onto the Fe* sites of the 3-MPA-modified Fe-Co-LDH via forming a stable Fe─As(III)─3-MPA─As(III)─Fe structure. This results in masking the active sites and interlayer channels of the Fe-Co-LDH nanozyme. As a result, the presence of As(III) as well as 3-MPA specifically inhibit the LDH-catalyzed chromogenic reaction. Based on the above principle, a colorimetric assay was designed for the determination of As(III). It provided linear response in the 0.10~8.33 µM As(III) concentration range and a detection limit as low as 35 nM. The assay was applied to the quantitation of As(III), even in the presence of potential interferents including As(V), Hg(II) and Pb(II), in environmental and drinking water samples. Graphical abstractSchematic illustration of the As(III) sensing mechanism based on 3-mercaptopropionic acid (3-MPA) assisted active site and interlayer channel dual-masking of Fe-Co-layered double hydroxides (Fe-Co-LDH) with oxidase-like activity. 3-MPA with sulfhydryl and carboxyl groups can assist As(III) to firmly anchor onto the Fe* sites inside the interlayer channels of the Fe-Co-LDH via forming a Fe─As(III)─3-MPA─As(III)─Fe structure, thus selectively resulting in a significant suppression of the chromogenic reaction.

Colorimetric evaluation of the hydroxyl radical scavenging ability of antioxidants using carbon-confined CoOx as a highly active peroxidase mimic.

The authors present a colorimetric method for the evaluation of the hydroxyl radical scavenging capability of antioxidants by exploiting carbon-confined mixed cobalt oxide nanoparticles (denoted as C-confined CoOx NPs) as a novel peroxidase mimic. The nanozyme can be prepared from the metal-organic framework ZIF-67 by calcination at a moderate temperature. It exhibits peroxidase-mimicking activity and catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue product in the presence of H2O2 via generation of hydroxyl radicals. However, in the presence of an antioxidant, the color reaction is suppressed due to scavenging of hydroxyl radicals by the antioxidant. Based on this principle, the hydroxy radical scavenging ability of glutathione (GSH), cysteine (Cys), tannic acid (TA) and tea polyphenols (TP) was assessed. It was found that these antioxidants can scavenge hydroxyl radicals in the following decreasing order: TA>Cys>GSH>TP. The assay was also used to quantify the antioxidative power of common fruit extracts. Graphical abstract Schematic presentation for evaluating the hydroxyl radical scavenging ability of different antioxidants using carbon-confined mixed cobalt oxide nanoparticles (denoted as C-confined CoOx NPs) as a highly active peroxidase mimic. With excellent activity, the C-confined CoOx NPs together with the visible peroxidase reaction can be employed as a powerful tool to rapidly screen appropriate antioxidants from natural samples and measure their activity for guiding their usage in related products.

Molecularly imprinted polymers as receptor mimics for selective cell recognition.

Molecularly imprinted polymers (MIPs) have now earned the reputation as "artificial receptors" or "plastic antibodies". As the mimics of natural receptors, MIPs are reminiscent of some basic functions of natural receptors in living systems, e.g., the ability to interact with or recognize cells. The latest decade has witnessed a great advance in MIPs from simple molecular extraction to efficient cell recognition, implying that MIP-based synthetic receptors are approaching to be perfectly functioning replicates of their natural counterparts. With the most emerging development in molecular imprinting, MIP-mediated cell recognition has now shown great promise in cell biology research, theranostics and regenerative medicine. This tutorial review provides a panoramic view of current MIPs for both microorganism and mammalian cell recognition. The most representative developments of MIP-mediated cell recognition, from initial imprinting strategies to eventual bio-related applications, are highlighted.

Dynamically PEGylated and Borate-Coordination-Polymer-Coated Polydopamine Nanoparticles for Synergetic Tumor-Targeted, Chemo-Photothermal Combination Therapy.

Multifunctional nanomaterials with efficient tumor-targeting and high antitumor activity are highly anticipated in the field of cancer therapy. In this work, a synergetic tumor-targeted, chemo-photothermal combined therapeutic nanoplatform based on a dynamically PEGylated, borate-coordination-polymer-coated polydopamine nanoparticle (PDA@CP-PEG) is developed. PEGylation on the multifunctional nanoparticles is dynamically achieved via the reversible covalent interaction between the surface phenylboronic acid (PBA) group and a catechol-containing poly(ethylene glycol) (PEG) molecule. Due to the acid-labile PBA/catechol complex and the weak-acid-stable PBA/sialic acid (SA) complex, the nanoparticles can exhibit a synergetic targeting property for the SA-overexpressed tumor cells, i.e., the PEG-caused "passive targeting" and PBA-triggered "active targeting" under the weakly acidic tumor microenvironment. In addition, the photothermal effect of the polydopamine core and the doxorubicin-loading capacity of the porous coordination polymer layer endow the nanoparticles with the potential for chemo-photothermal combination therapy. As expected, the in vitro and in vivo studies both verify that the multifunctional nanoparticles possess relatively lower systematic toxicity, efficient tumor targeting ability, and excellent chemo-photothermal activity for tumor inhibition. It is believed that these multifunctional nanoparticles with synergetic tumor targeting property and combined therapeutic strategies would provide an insight into the design of a high-efficiency antitumor nanoplatform for potential clinical applications.