Magnetic Ni/Fe layered double hydroxide nanosheets as enhancer for DNA hairpin sensitive detection of miRNA

Controllable Synthesis of Hemoglobin-Metal Phosphate Organic-Inorganic Hybrid Nanoflowers and Their Applications in Biocatalysis

In recent years, organic-inorganic hybrid nanoflower technology has become an effective method for enzyme immobilization. Here, seven hierarchical flower-like hemoglobin-phosphate organic-inorganic hybrid nanomaterials (Hb-M3(PO4)2·nH2O HNFs) were synthesized through an improved universal one-pot wet-chemical method, with Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ as inorganic components. In this synthesis process, the metal cations are successively involved in the coordination reaction with Hb and the metathesis reaction to generate phosphate precipitation. The coordination ability of metal cations and the generation rate of phosphate precipitations were evaluated, then the progress of the two chemical reactions was controlled synchronously by adjusting the phosphate buffer (PB) concentration, and finally a flower-like structure conducive to substrate diffusion and transport was obtained. Due to the conformational transformation of hemoglobin and the abundant Cu2+/Fe3+ active sites, the hemoglobin-Cu3(PO4)2·3H2O nanoflowers have extremely high catalytic activity, which is ∼14 times that of Hb. Importantly, this method is suitable for the monometallic-ionic, polymetallic-ionic and polyvalent metal-ion nanoflowers, which broadens the chemical composition and structural diversity of nanoflowers.

Surface modification of two-dimensional layered double hydroxide nanoparticles with biopolymers for biomedical applications

Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested.

Application of CoMn/CoFe layered double hydroxide based on metal-organic frameworks template to activate peroxymonosulfate for 2,4-dichlorophenol degradation

Metal-organic frameworks (MOFs) have unique properties and stable structures, which have been widely used as templates/precursors to prepare well developed pore structure and high specific surface area materials. In this article, an innovative and facile method of crystal reorganization was designed by using MOFs as sacrificial templates to prepare a layered double hydroxide (LDH) nano-layer sheet structure through a pseudomorphic conversion process under alkaline conditions. The obtained CoMn-LDH and CoFe-LDH catalysts broke the ligand of MOFs and reorganized the structure on the basis of retaining a high specific surface area and a large number of pores, which had higher specific surface area and well developed pore structure compared with LDH catalysts prepared by traditional methods, and thus provide more active sites to activate peroxymonosulfate (PMS). Due to the unique framework structure of MOFs, the MOF-derived CoMn-LDH and CoFe-LDH catalysts could provide more active sites to activate PMS, and achieve a 2,4-dichlorophenol degradation of 99.3% and 99.2% within 20 minutes, respectively. In addition the two LDH catalysts displayed excellent degradation performance for bisphenol A, ciprofloxacin and 2,4-dichlorophenoxyacetic acid (2,4-D). X-ray photoelectron spectroscopy indicated that the valence state transformation of metal elements participated in PMS activation. Electron paramagnetic resonance manifested that sulfate radical (SO₄^•-) and singlet oxygen (¹O₂) were the main species for degrading pollutants. In addition, after the three-cycle experiment, the CoMn-LDH and CoFe-LDH catalysts also showed long-term stability with a slight activity decrease in the third cycle. The phytotoxicity assessment determined by the germination of mung beans proved that PMS activation by MOF-derived LDH catalysts can basically eliminate the phytotoxicity of a 2,4-D solution. This research not only developed high-activity LDH catalysts for PMS activation, but also expanded the environmental applications of MOF derivants.

Multiply-amplified strategy for the ultrasensitive detection of kanamycin via aptamer-triggered three-dimensional G-quadruplex/Ni-Fe layered double oxide frame networks

In this work, a multiply-amplified peroxidase-like colorimetric strategy was proposed for the high-specific recognition and ultrasensitive detection of kanamycin (Kana). Based on two Kana-aptamer triggered sequential reactions, G-quadruplex (G4) and DNA (hairpins) modified Ni-Fe layered double oxides (LDOs) could be obtained simultaneously. Later, a three-dimensional G4/LDO frame networks, as a novel DNAzyme, with enhanced peroxidase-like catalytic activity was assembled through electrostatic interaction. This DNAzyme catalyzed 3,3',5,5'-tetramethylbenzidine oxidation for the colorimetric detection of Kana. The enhancement principle was discussed and the charge transfer process during the catalytic reaction was investigated. Under the optimal experiment conditions, the proposed method exhibited high sensitivity, where the linear range is from 10 fM to 10 nM (r² = 0.992), and the limit of detection is 3 fM (S/N = 3). The practicability of this assay was demonstrated by successfully application of residual Kana detection in genuine milk and urine samples.

Ni/Fe layered double hydroxide nanosheet/G-quadruplex as a new complex DNAzyme with highly enhanced peroxidase-mimic activity

A novel and low-cost DNAzyme, Ni/Fe layered double hydroxide (LDH) nanosheet/G-quadruplex (without hemin) with enhanced peroxidase-mimic activity was designed. The catalytic mechanism was investigated. The detection of Cu(II) in actual serum samples could be realized sensitively via this efficient DNAzyme-based method.

Amino-based magneto-polymeric-modified mixed iron hydroxides for magnetic solid phase extraction of phenol residues in environmental samples

Mixed iron hydroxides (MIHs) modified with different amino-based polymeric materials, including aminopropyltriethoxysilane, polydopamine, diaminobenzoic acid, polyaniline, and polyphenylenediamine, were comparatively investigated as sorbents for the extraction of phenol compounds. Polyphenylenediamine-modified mixed iron hydroxides (MIH@PPDA) showed high adsorption capability for most target analytes. Its ferromagnetic behavior, with a magnetization of 17.38 emu g^-1, was sufficient for subsequent use in magnetic solid-phase extraction (MSPE). The functional groups, morphology, and magnetic properties of this magnetic nanomaterial were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, X-ray diffraction, and CHN analysis. High-performance liquid chromatography with a photodiode array detector was used to quantify phenol compounds. The experimental parameters affecting the efficiency of the entire MSPE process were optimized. Good linearity in the range of 0.5-1000 µg L^-1 was obtained (depended on the compound). The detection and quantitation limits varied from 0.01 to 0.3 µg L^-1 and 0.03 to 0.9 µg L^-1, respectively. The enrichment factors for all phenol compounds were in the range of 80-285. The precision in terms of intra- and inter-day relative standard deviations were below 5.8% and 6.2%, respectively. The developed MSPE method was applied to analyze phenol compounds in diverse samples, including soil, drinking water, and fruit. Relative recoveries of 76.7-130.1% were obtained. The MIH@PPDA magneto-polymeric sorbent exhibits good stability and is reliable for a variety of phenol compounds.

A review on optical sensors based on layered double hydroxides nanoplatforms

In recent years, significant efforts have been devoted towards the fabrication and application of layered double hydroxides (LDHs) due to their tremendous features such as excellent biocompatibility with negligible toxicity, large surface area, high conductivity, excellent solubility, and ion exchange properties. Most impressive, LDHs offer a favorable environment to attach several substances such as quantum dots, fluorescein dyes, proteins, and enzymes, which leads to strengthening the catalytic properties or increasing the sensing selectivity and sensitivity of the resulted hybrids. With the extensive ongoing research on the application of nanomaterials, many studies have led to remarkable achievements in exploring LDHs as sensing nanoplatforms. In optical sensors, for instance, many sensing strategies were tailored based on the enzyme-mimicking properties of LDHs, including colorimetric and chemiluminescence procedures. Meanwhile, others were designed based on intercalating some fluorogenic substrates on the LDHs, whereby the sensing signal can be acquired by quenching or enhancing their fluorescence after the addition of analytes. In this review, we aim to summarize the recent advances in optical sensors that use layered double hydroxides as sensing platforms for the determination of various analytes. By outlining some representative examples, we accentuate the change of spectral absorbance, chemiluminescence, and photoluminescence phenomena triggered by the interaction of LDH or functionalized-LDH with the indicators and analytes in the system. And finally, current limitations and possible future orientation in designing further LDHs-based optical sensors are presented. It is hoped that this review will be helpful in assisting the establishment of more improved sensors based on LDHs features. Optical sensors based on layered double hydroxides (LDHs) nanoplatforms were reviewed. The sensing system and detection approaches were rationally reviewed. Possible future orientations were highlighted.

Iron-Based Nanozymes in Disease Diagnosis and Treatment

Iron-based nanozymes are currently one of the few clinical inorganic nanoparticles for disease diagnosis and treatment. Overcoming the shortcomings of natural enzymes, such as easy inactivation and low yield, combined with their special nanometer properties and magnetic functions, iron-based nanozymes have broad prospects in biomedicine. This minireview summarizes their preparation, biological activity, catalytic mechanism, and applications in diagnosis and treatment of diseases. Finally, challenges to their future development and the trends of iron-based nanozymes are discussed. The purpose of this minireview is to better understand and reasonably speculate on the rational design of iron-based nanozymes as an increasingly important new paradigm for diagnostics.

Recent advances in the application of layered double hydroxides in analytical chemistry: A review

In recent years, layered double hydroxides (LDHs) have garnered a lot of attention in analytical chemistry, due to their advantages such as relatively simple synthesis, low cost, possession of large specific surface area and high catalytic activity, and biocompatibility. The most common applications of LDH in analytical chemistry such as sorbents in sample extraction, electrode materials in electrochemical sensing and color indicators in colorimetric detection have been well reported. Generally, the LDHs are prepared as composites with nanomaterials, or constructed with specific three-dimensional structures, befitting the applications desired for them. However, the applications of LDHs (as extraction sorbents, color indicators and in electrochemical sensing) are usually limited in these scenarios. To help address these challenges, future trends and developmental prospects of LDHs materials in analytical chemistry are discussed in this article. Besides, the strategies associated with the design of LDHs, including the structural aspects, for potential analytical applications are presented and reviewed.

A triple-amplification strategy based on the formation of peroxidase-like two-dimensional DNA/Fe3O4 networks initiated by the hybridization chain reaction for highly sensitive detection of microRNA

Peroxidase-like two-dimensional DNA/Fe₃O₄ networks were constructed by the hybridization chain reaction and applied to detect microRNA down to the aM level.

Functional nanomaterials with unique enzyme-like characteristics for sensing applications

We highlight the recent developments in functional nanomaterials with unique enzyme-like characteristics for sensing applications.