Adsorption of Oligo-DNA on Magnesium Aluminum-Layered Double-Hydroxide Nanoparticle Surfaces: Mechanistic Implication in Gene Delivery

Synthesis of Water-Soluble Planar Cobalt(II), Nickel(II), and Copper(II) Hydroxo Clusters Using a (1,4,7-Triazacyclononane)cobalt(III) Complex as a Hydrolysis-Terminating Group

We report on a group of planar cobalt(II), nickel(II), and copper(II) hydroxo clusters that have a definite composition and are water-soluble: [{Co(tacn)(OH)₂}₆Co₇(OH)₁₂](NO₃)₂(CF₃SO₃)₆·10H₂O (1), [{Co(tacn)(OH)₂}₆Ni₇(OH)₁₂](NO₃)₂(CF₃SO₃)₆·10H₂O (2a), [{Co(tacn)(OH)₂}₆Ni₇(OH)₁₂](BNPP)₈·6CH₃NO₂·8H₂O [2b; BNPP = bis(p-nitrophenyl)phosphate], [{Co(tacn)(OH)₂}₁₂Ni₁₆(OH)₂₆(OH₂)₂](SO₄)₄(CF₃SO₃)₁₀·30H₂O (3a), [{Co(tacn)(OH)₂}₁₂Ni₁₆(OH)₂₆(OH₂)₂](SO₄)₈(CF₃SO₃)₂·44H₂O (3b), [{Co(tacn)(OH)₂}₂Co₂(OH)₂(OH₂)₄](SO₄)(CF₃SO₃)₂·4H₂O (4), [{Co(tacn)(OH)₂}₂Ni₂(OH)₂(OH₂)₄](SO₄)(CF₃SO₃)₂·4H₂O (5), and [{Co(tacn)(OH)₂}₄Cu₄(OH)₆](ClO₄)₆·5H₂O (6), where tacn is 1,4,7-triazacyclononane. The peripheral of each metal hydroxo cluster plane is chemically protected by the coordination of {Co^III(tacn)(OH)₂}⁺ groups to prevent further hydrolysis. These clusters were synthesized by the reaction of an equimolar amount of [Co(tacn)(OH₂)₃]³⁺ and cobalt, nickel, or copper salt at pH values in the range of 6.0-12.0. The structure of the cation in compounds 1, 2a or 2b, 4, and 5 is relevant to the surface structure of the cobalt phosphate and nickel borate oxygen-evolution catalysts; in particular, the Co₇(OH)₁₂ core in 1. Moreover, the arrangement of M₇(OH)₁₂ in 1 and 2a or 2b and Cu₄(OH)₆ in 6 represents the solid-state structures of the (111) face of the cubic CoO or NiO and the (002) plane of Cu(OH)₂, respectively. Extended X-ray absorption fine structure spectra of an aqueous solution of 1, 2a, 4, and 5 exhibit well-resolved peaks at the first and second coordination spheres due to the M-O and M···M distances, respectively; the solution-state bond distances were estimated, and they agreed well with the bond distances in the solid-state structures.

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.

Biofunctional Layered Double Hydroxide Nanohybrids for Cancer Therapy

Layered double hydroxides (LDHs) with two-dimensional nanostructure are inorganic materials that have attractive advantages such as biocompatibility, facile preparation, and high drug loading capacity for therapeutic bioapplications. Since the intercalation chemistry of DNA molecules into the LDH materials were reported, various LDH nanohybrids have been developed for biomedical drug delivery system. For these reasons, LDHs hybridized with numerous therapeutic agents have a significant role in cancer imaging and therapy with targeting functions. In this review, we summarized the recent advances in the preparation of LDH nanohybrids for cancer therapeutic strategies including gene therapy, chemotherapy, immunotherapy, and combination therapy.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

Oligonucleotide-Functionalized Enzymes Chemisorbing on Magnetic Layered Double Hydroxides: A Multimodal Catalytic Platform with Boosted Activity for Ultrasensitive Glucose Detection

A reasonable design of multifarious chemo- and biocatalytic functions within individual nano/microunits is urgently desired for high-performance cascade reactions but has heretofore remained elusive. Herein, glucose oxidase was functionalized with oligonucleotides and steadily chemisorbed on magnetic layered double hydroxides (mLDHs) to construct a multimodal catalytic platform for realizing divergent reactions with heterogeneous and biocatalytic steps. The flowerlike mLDHs served both as an enzyme support and a peroxidase mimic cooperating with enzymes for tandem catalysis. Oligo-DNA connected the enzymes to mLDHs like a bridge, and a stepwise ligand-exchange-assisted coordination mechanism was proposed to explain the robust interaction between DNA and mLDHs. More importantly, DNA significantly improved the bioactivity of the whole system. The acceleration mechanism was attributed to the diffusion tunnels for the substrate/product and enhanced substrates binding on mLDHs. The multimodal catalytic platform was applied for colorimetric and electrochemical sensing of glucose with a low limit of detection and high selectivity. The practical analysis capability of the ultrasensitive sensor was evaluated by detecting glucose in human serum and sweat, showing reliable results, satisfactory recovery, and excellent stability. The strategy of combining mLDHs and enzymes for cascade catalysis provides a universal approach to prepare chemo-enzyme hybrids with high performance, which holds great promise for applications in biosensors and industrial catalysis.

Polyvalent Metal Ion Promoted Adsorption of DNA Oligonucleotides by Montmorillonite

Montmorillonite (MMT) is a two-dimensional (2D) clay material. Its abundance on the early earth has attracted studies for its role in prebiotic reactions, and adsorption of DNA to MMT is potentially important for understanding the origin of life. Although several possible models of DNA adsorption on MMT have been established, a consensus on the adsorption mechanism has yet to be formed, thereby a fundamental adsorption study is performed here. Adding up to 300 mM NaCl failed to promote DNA adsorption on MMT, Al₂O₃, or SiO₂ nanoparticles. For polyvalent metals, DNA adsorption was achieved following the order Ce³⁺ > Cu²⁺ > Ni²⁺ > Zn²⁺. Among them, Ce³⁺ and Cu²⁺ inverted the surface charge of MMT to positive. In addition, using washing experiments, Cu²⁺- and Ce³⁺-mediated adsorption mainly depended on the DNA phosphate backbone, while Ni²⁺ and Zn²⁺ interacted with the backbone phosphate groups and adenine bases of DNA. Overall, these polyvalent metal ions promoted DNA adsorption via a cation bridge model. This research provides new insights into the surface interactions of MMT and DNA, which is conducive to future work on the interaction between clays and biopolymers.

Advanced drug delivery applications of layered double hydroxide

Layered double hydroxides (LDHs), also known as anionic clays or hydrotalcite-like compounds, are a class of nanomaterials that attained great attention as a carrier for drug delivery applications. The lamellar structure of this compound exhibits a high surface-to-volume ratio which enables the intercalation of therapeutic agents and releases them at the target site, thereby reducing the adverse effect. Moreover, the intercalated drug can be released in a sustained manner, and hence the frequency of drug administration can be decreased. The co-precipitation, ion exchange, manual grinding, and sol-gel methods are the most employed for their synthesis. The unique properties like the ease of synthesis, low cost, high biocompatibility, and low toxicity render them suitable for biomedical applications. This review presents the advances in the structure, properties, method of preparation, types, functionalization, and drug delivery applications of LDH. Also, this review provides various new conceptual insights that can form the basis for new research questions related to the drug delivery applications of LDH.

Layered Double Hydroxide as a Potent Non-viral Vector for Nucleic Acid Delivery Using Gene-Activated Scaffolds for Tissue Regeneration Applications

Nonviral vectors offer a safe alternative to viral vectors for gene therapy applications, albeit typically exhibiting lower transfection efficiencies. As a result, there remains a significant need for the development of a nonviral delivery system with low cytotoxicity and high transfection efficacy as a tool for safe and transient gene delivery. This study assesses MgAl-NO₃ layered double hydroxide (LDH) as a nonviral vector to deliver nucleic acids (pDNA, miRNA and siRNA) to mesenchymal stromal cells (MSCs) in 2D culture and using a 3D tissue engineering scaffold approach. Nanoparticles were formulated by complexing LDH with pDNA, microRNA (miRNA) mimics and inhibitors, and siRNA at varying mass ratios of LDH:nucleic acid. In 2D monolayer, pDNA delivery demonstrated significant cytotoxicity issues, and low cellular transfection was deemed to be a result of the poor physicochemical properties of the LDH–pDNA nanoparticles. However, the lower mass ratios required to successfully complex with miRNA and siRNA cargo allowed for efficient delivery to MSCs. Furthermore, incorporation of LDH–miRNA nanoparticles into collagen-nanohydroxyapatite scaffolds resulted in successful overexpression of miRNA in MSCs, demonstrating the development of an efficacious miRNA delivery platform for gene therapy applications in regenerative medicine.

ZnAl nano layered double hydroxides for dual functional CRISPR/Cas9 delivery and enhanced green fluorescence protein biosensor

Evaluation of the effect of different parameters for designing a non-viral vector in gene delivery systems has great importance. In this manner, 2D crystals, precisely layered double hydroxides, have attracted the attention of scientists due to their significant adjustability and low-toxicity and low-cost preparation procedure. In this work, the relationship between different physicochemical properties of LDH, including pH, size, zeta potential, and synthesis procedure, was investigated and optimized for CRISPR/Cas9 delivery and reverse fluorescence response to the EGFP. In this manner, ZnAl LDH and ZnAl HMTA LDH were synthesized and characterized and applied in the HEK-293 cell line to deliver CRISPR/Cas9. The results were optimized by different characterizations as well as Gel Electrophoresis and showed acceptable binding ability with the DNA that could be considered as a promising and also new gold-standard for the delivery of CRISPR/Cas9. Also, the relationship of the presence of tertiary amines (in this case, hexamethylenetetramine (HMTA) as the templates) in the structure of the ZnAl LDH, as well as the gene delivery application, was evaluated. The results showed more than 79% of relative cell viability in most of the weight ratios of LDH to CRISPR/Cas9; fully quenching the fluorescence intensity of the EGFP/LDH in the presence of 15 µg mL-1 of the protoporphyrins along with the detection limit of below 2.1 µg mL-1, the transfection efficiency of around 33% of the GFP positive cell for ZnAl LDH and more than 38% for the ZnAl LDH in the presence of its tertiary amine template.

CoAl-layered double hydroxide nanosheet-based fluorescence assay for fast DNA detection

In the study, CoAl-layered double hydroxide (CoAl-LDH) was prepared as a fluorescence quenching agent to detect DNA molecules. Because of its simple preparation for a large scale, excellent surface effect, good biocompatibility and high fluorescence quenching capability, the effective, rapid, and sensitive DNA detection was realized. The fluorescence quenching efficiency of LDH to 5(6)-carboxyfluorescein attached to single stranded DNA (FAM-ssDNA) was as high as 88%, and after FAM-ssDNA hybridized with the complementary DNA oligonucleotide, that to FAM-dsDNA was about 33%. The quenching mechanisms of LDH for ssDNA and dsDNA were discussed. Phosphate exposed of ssDNA played an important role in quenching effect. Compared to dsDNA, more exposed phosphate groups in ssDNA resulted in the stronger electrostatic interaction between ssDNA and LDH, and thus the higher quenching efficiency. Under optimal conditions, the linear equation was y = 38.26 + 3.37x in a linear relationship of 1-50 nM, and the correlation coefficient R² corresponded to 0.999, and the limit of detection was calculated to be 0.79 nM (3σ). Cytotoxicity studies have shown that LDH has good biocompatibility. The study provides an effective, sensitive and safe approach for DNA detection and gives an insight for the design of LDH-based biosensing materials.

Layered Double Hydroxides: A Toolbox for Chemistry and Biology

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO2 conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects.

Charge-Dependent Regulation in DNA Adsorption on 2D Clay Minerals

DNA purification is essential for the detection of human clinical specimens. A non-destructive, controllable, and low reagent consuming DNA extraction method is described. Negatively charged DNA is absorbed onto a negatively charged montmorillonite to achieve non-destructive DNA extraction based on cation bridge construction and electric double layer formation. Different valence cation modified montmorillonite forms were used to validate the charge-dependent nature of DNA adsorption on montmorillonite. Electric double layer thickness thinning/thickening with the high/lower valence cations exists, and the minerals tended to be sedimentation-stable due to the Van der Waals attraction/electrostatic repulsion. Li-modified montmorillonite with the lowest charge states showed the best DNA adsorption efficiency of 8–10 ng/μg. Charge-dependent regulating research provides a new perspective for controllable DNA extraction and a deep analysis of interface engineering mechanisms.

A fluorometric displacement assay for adenosine triphosphate using layered cobalt(II) double hydroxide nanosheets

A turn-on fluorometric method is described for the determination of adenosine-5'-triphosphate (ATP). It is based on the displacement of a dye-labeled oligonucleotide from a cobalt(II) based layered double hydroxide (LDH). Due to the electrostatic and ligand exchange interaction, the FAM-labeled DNA is readily adsorbed on the LDH. This leads to complete and fast quenching of the green fluorescence of the label. However, on addition of ATP, the DNA is detached from the LDH because of the stronger affinity of ATP for LDH. This results in the restoration of the green fluorescence. The effect was used to design a sensitive assay that has a linear response in the 0.5-100 μM ATP concentration range and a 0.23 μM lower detection limit. It was applied to the determination of ATP in spiked serum samples. Graphical abstract Schematic presentation of a fluorometric ATP assay based on the displacement of a dye-labeled oligonucleotide from a layered double hydroxide (LDH).

Optimization of Formulations Consisting of Layered Double Hydroxide Nanoparticles and Small Interfering RNA for Efficient Knockdown of the Target Gene

Layered double hydroxide (LDH) nanoparticles (NPs) are safe and effective vectors for small interfering RNA (siRNA) delivery. However, it is unclear whether there are optimal parameters for the efficient delivery of functional siRNA using LDH NPs. In this research, we comprehensively examined the effect of parameters, such as the mixing method and LDH/siRNA mass ratio on siRNA silencing capability. We first noted that the best way for loading gene segments (25 bp dsDNA and siRNA) is to add gene molecules to 100 nm LDH and then diluting in Dulbecco's modified Eagle's medium. Very interestingly, the optimal LDH/gene mass ratio is around 20:1 in terms of cellular uptake amount of gene segments, whereas this ratio is shifted to around 5:1 in terms of target gene silencing efficacy, which has been reasonably explained. The optimization for LDH NP-based gene delivery system may provide the guidance for more efficient in vitro and in vivo siRNA delivery using the optimal parameters.

Enhancing the Therapeutic Delivery of Oligonucleotides by Chemical Modification and Nanoparticle Encapsulation

Oligonucleotide (ON) drugs, including small interfering RNA (siRNA), microRNA (miRNA) and antisense oligonucleotides, are promising therapeutic agents. However, their low membrane permeability and sensitivity to nucleases present challenges to in vivo delivery. Chemical modifications of the ON offer a potential solution to improve the stability and efficacy of ON drugs. Combined with nanoparticle encapsulation, delivery at the site of action and gene silencing activity of chemically modified ON drugs can be further enhanced. In the present review, several types of ON drugs, selection of chemical modification, and nanoparticle-based delivery systems to deliver these ON drugs are discussed.