Transition Metal-Mediated DNA Adsorption on Polydopamine Nanoparticles

Three musketeers of PDA-based MRI contrasting and therapy

Polydopamine (PDA) stands as a versatile material explored in cancer nanomedicine for its unique properties, offering opportunities for multifunctional drug delivery platforms. This study explores the potential of utilizing a one-pot synthesis to concurrently integrate Fe, Gd and Mn ions into porous PDA-based theranostic drug delivery platforms called Ferritis, Gadolinis and Manganis, respectively. Our investigation spans the morphology, magnetic properties, photothermal characteristics and cytotoxicity profiles of those potent nanoformulations. The obtained structures showcase a spherical morphology, robust magnetic response and promising photothermal behaviour. All of the presented nanoparticles (NPs) display pronounced paramagnetism, revealing contrasting potential for MRI imaging. Relaxivity values, a key determinant of contrast efficacy, demonstrated competitive or superior performance compared to established, used contrasting agents. These nanoformulations also exhibited robust photothermal properties under near infra-red irradiation, showcasing their possible application for photothermal therapy of cancer. Our findings provide insights into the potential of metal-doped PDA NPs for cancer theranostics.

Isopropanol-promoted DNA extraction by polydopamine functionalized magnetic particles based on metal coordination

High-quality DNA is an important guarantee to start downstream experiments in many biological and medical research areas. Magnetic particle-based DNA extraction methods from blood mainly depend on electrostatic adsorption in a low-pH environment. However, the strong acidic environment can influence the DNA stability. Herein, a polydopamine-functionalized magnetic particle (PDA@Fe3O4)-based protocol was developed for DNA extraction from whole blood samples. In the protocol, Mg2+ and Ca2+ were utilized to bridge the adsorption of DNA by PDA@Fe3O4 via the metal-mediated coordination. Isopropanol was found to efficiently promote DNA adsorption by triggering the change of the conformation of DNA from B-form to more compact A-form. In 50 % isopropanol solution, the DNA adsorption efficiency was nearly 100 % in the presence of 0.5 mM Ca2+ or 1.5 mM Mg2+. The role of metal ions and isopropanol in DNA adsorption was explored. The protocol averts the strong acidic environment and PCR inhibitors, such as high concentrations of salt or polyethylene glycol. It demonstrates superiority in DNA yield (59.13 ± 3.63 ng μL-1) over the commercial kit (27.33 ± 4.98 ng μL-1) and phenol-chloroform methods (37.90 ± 0.47 ng μL-1). In addition, to simplify the operastion, an automated nucleic acid extraction device was designed and fabricated to extract whole genomic DNA from blood. The feasibility of the device was verified by extracting DNA from cattle and pig blood samples. The extracted DNA was successfully applied to discriminate the beef authenticity by a duplex PCR system. The results demonstrate that the DNA extraction protocol and the automated device have great potential in blood samples.

Sunflower Pollen-Derived Microspheres Selectively Absorb DNA for microRNA Detection

Herein, we report the finding that a naturally sunflower pollen-derived microspheres (HSECs) with hierarchical structures can selectively absorb polyC and polyA with high efficiency and affinity. HSECs exhibit the capability to selectively absorb polyC and polyA ssDNA under neutral and acidic conditions. It has been observed that the presence of metal cations, specifically Ca2+, enhances the absorption efficiency of HSECs. Mechanically, this absorption phenomenon can be attributed to both electrostatic interactions and cation-π interactions. Such an appealing property enables the functionalization of HSECs for broad potential biomedical applications, such as microRNA detection.

Mg2+-promoted high-efficiency DNA conjugation on polydopamine surfaces for aptamer-based ochratoxin A detection

BACKGROUND

Surface immobilization of DNA is the foundation of a broad range of applications in biosensing and specific DNA extraction. Polydopamine (PDA) coatings can serve as intermediate layers to immobilize amino- or thiol-labelled molecules, including DNA, onto various materials through Michael addition and/or Schiff base reactions. However, the conjugation efficiency is limited by electrostatic repulsion between negatively charged DNA and PDA. Recently, it has been reported that polyvalent metal ions (such as Mg2+ and Ca2+) can mediate the adsorption of DNA on PDA surfaces. Inspired by this, in this work we aimed to exploit polyvalent metal ions to facilitate the conjugation of DNA on PDA.

RESULTS

Mg2+ was used to promote the conjugation of amino-terminated DNA complementary to ochratoxin A (OTA) aptamer (cDNA-NH2) on PDA-coated magnetic nanoparticles (Fe3O4@PDA). After the reaction, the unlinked cDNA-NH2 adsorbed on Fe3O4@PDA mediated by Mg2+ was removed with EDTA. In the presence of 20 mM Mg2+, the amount of covalently linked cDNA-NH2 increased approximately 11-fold compared to that in the absence of Mg2+. The resulting Fe3O4@PDA@cDNA conjugates exhibited superior hybridization capacity towards OTA aptamers, minimal nonspecific adsorption, and excellent chemical stability. The conjugates combined with fluorophore-labelled aptamers were employed for OTA detection, achieving a limit of detection (LOD) of 2.77 ng mL-1. To demonstrate versatility, this conjugation method was extended to Ca2+-promoted conjugation of cDNA-NH2 on Fe3O4@PDA nanoparticles and Mg2+-promoted conjugation of cDNA-NH2 on PDA-coated 96-well plates.

SIGNIFICANCE

The conjugation efficiency of DNA on PDA was significantly improved with the assistance of polyvalent metal ions (Mg2+ and Ca2+), providing a facile and efficient method for DNA immobilization. Due to the substrate-independent adhesion property of PDA, this method demonstrates versatility in DNA surface modification and holds great potential for applications in target extraction, biosensing, and other fields.

Mg2+- or Ca2+-regulated aptamer adsorption on polydopamine-coated magnetic nanoparticles for fluorescence detection of ochratoxin A

It has been observed that polyvalent metal ions can mediate the adsorption of DNA on polydopamine (PDA) surfaces. Exploiting this, we used two divalent metal ions (Mg2+ or Ca2+) to promote the adsorption of fluorescence-labelled ochratoxin A (OTA) aptamers on PDA-coated magnetic nanoparticles (Fe3O4@PDA). Based on the different adsorption affinities of free aptamers and OTA-bound aptamers, a facile assay method was established for OTA detection. The aptamers adsorbed on Fe3O4@PDA were removed via simple magnetic separation, and the remaining aptamers in the supernatant exhibited a positive correlation with the OTA concentration. The concentrations of Mg2+ and Ca2+ were finely tuned to attain the optimal adsorption affinity and sensitivity for OTA detection. In addition, other factors, including the Fe3O4@PDA dosage, pH, mixing order, and incubation time, were studied. Finally, under optimized conditions, a detection limit (3σ/s) of 1.26 ng/mL was achieved for OTA. Real samples of spiked red wine were analysed with this aptamer-based method. This is the first report of regulating aptamer adsorption on the PDA surface with polyvalent metal ions for OTA detection. By changing the aptamers, the method can be easily extended to other target analytes.

Flexible Conductive Decellularized Fish Skin Matrix as a Functional Scaffold for Myocardial Infarction Repair

Engineering cardiac patches are proven to be effective in myocardial infarction (MI) repair, but it is still a tricky problem in tissue engineering to construct a scaffold with good biocompatibility, suitable mechanical properties, and solid structure. Herein, decellularized fish skin matrix is utilized with good biocompatibility to prepare a flexible conductive cardiac patch through polymerization of polydopamine (PDA) and polypyrrole (PPy). Compared with single modification, the double modification strategy facilitated the efficiency of pyrrole polymerization, so that the patch conductivity is improved. According to the results of experiments in vivo and in vitro, the scaffold can promote the maturation and functionalization of cardiomyocytes (CMs). It can also reduce the inflammatory response, increase local microcirculation, and reconstruct the conductive microenvironment in infarcted myocardia, thus improving the cardiac function of MI rats. In addition, the excellent flexibility of the scaffold, which enables it to be implanted in vivo through "folding-delivering-re-stretehing" pathway, provides the possibility of microoperation under endoscope, which avoids the secondary damage to myocardium by traditional thoracotomy for implantation surgery.

Fibrous MXene Aerogels with Tunable Pore Structures for High-Efficiency Desalination of Contaminated Seawater

The seawater desalination based on solar-driven interfacial evaporation has emerged as a promising technique to alleviate the global crisis on freshwater shortage. However, achieving high desalination performance on actual, oil-contaminated seawater remains a critical challenge, because the transport channels and evaporation interfaces of the current solar evaporators are easily blocked by the oil slicks, resulting in undermined evaporation rate and conversion efficiency. Herein, we propose a facile strategy for fabricating a modularized solar evaporator based on flexible MXene aerogels with arbitrarily tunable, highly ordered cellular/lamellar pore structures for high-efficiency oil interception and desalination. The core design is the creation of 1D fibrous MXenes with sufficiently large aspect ratios, whose superior flexibility and plentiful link forms lay the basis for controllable 3D assembly into more complicated pore structures. The cellular pore structure is responsible for effective contaminants rejection due to the multi-sieving effect achieved by the omnipresent, isotropic wall apertures together with underwater superhydrophobicity, while the lamellar pore structure is favorable for rapid evaporation due to the presence of continuous, large-area evaporation channels. The modularized solar evaporator delivers the best evaporation rate (1.48 kg m-2 h-1) and conversion efficiency (92.08%) among all MXene-based desalination materials on oil-contaminated seawater.

Metal-Organic Frameworks Nanocarriers for Functional Nucleic Acid Delivery in Biomedical Applications

Metal-organic frameworks (MOFs), a distinctive funtionalmaterials which is constructed by various metal ions and organic molecules, have gradually attracted researchers' attention from they were founded. In the last decade, MOFs emerge as a biomedical material with potential applications due to their unique properties. However, the MOFs performed as nanocarriers for functional nucleic acid delivery in biomedical applications rarely summarized. In this review, we introduce recent developments of MOFs for nucleic acid delivery in various biologically relevant applications, with special emphasis on cancer therapy (including siRNA, ASO, DNAzyme, miRNA and CpG oligodeoxynucleotides), bioimaging, biosensors and separation of biomolecules. We expect the accomplishment of this review could benefit certain researchers in biomedical field to develop novel sophisticated nanocarriers for functional nucleic acid delivery based on the promising material of MOFs.

Adsorption of Linear and Spherical DNA Oligonucleotides onto Microplastics

Microplastic pollution of water and food chains can endanger human health. It has been reported that environmental DNA can be carried by microplastics and spread into the ecosystem. To better comprehend the interactions between microplastics and DNA, we herein investigated the adsorption of DNA oligonucleotides on a few important microplastics. The microplastics were prepared using common plastic objects made of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), composite of PS/PVC, and polyethylene terephthalate (PET). The effect of environmentally abundant metal ions such as Na⁺, Mg²⁺, and Ca²⁺ on the adsorption was also studied. Among the microplastics, PET and PS had the highest efficiency for the adsorption of linear DNA, likely due to the interactions provided by their aromatic rings. The study of DNA desorption from PET revealed the important role of hydrogen bonding and metal-mediated adsorption, while van der Waals force and hydrophobic interactions were also involved in the adsorption mechanism. The adsorption of spherical DNA (SNA) made of a high density of DNA coated on gold nanoparticles (AuNPs) was also studied, where the adsorption affinity order was found to be PET > PS/PVC > PS. Moreover, a tighter DNA adsorption was achieved in the presence of Ca²⁺ and Mg²⁺ compared to Na⁺.

Engineering CXCL12 Biomimetic Decoy-Integrated Versatile Immunosuppressive Nanoparticle for Ischemic Stroke Therapy with Management of Overactivated Brain Immune Microenvironment

Following ischemic stroke, brain-resident activated microglia and peripherally infiltrated inflammatory cells create a complicated and overactivated brain immune microenvironment, which causes neuron death and dramatically hinders neurological functional recovery. Herein, an engineering CXCL12 biomimetic decoy-integrated versatile immunosuppressive nanoparticle (VIN) for management of the overactivated brain immune microenvironment is reported. The shell of VIN (membrane of CXCR4 overexpressed mesenchymal stem cells), can not only improve the homing of nanoparticles to the cerebral ischemic lesions, but also efficiently adsorb and neutralize CXCL12 to cut off infiltration of peripheral-neutrophils and mononuclear macrophages. The loaded A151 (cGAS inhibitor, telomerase repeat sequences) can inhibit cGAS-STING pathway in microglia, leading to microglia polarization toward an anti-inflammatory M2-like phenotype. Interestingly, A151 can be efficiently loaded onto the polydopamine nanospheres (PDA, the core of VIN) through the bridge of Zn²⁺ . In the inflammatory site, PDA is oxidized by reactive oxygen species (ROS), with the disappearance of Zn²⁺ complexation effect, and then A151 realizes a controlled release. In a model of rat ischemic stroke, VIN integrates inflammation tropism, peripherally inflammatory cells filtrate, brain-resident activated microglia polarization, as well as, ROS scavenging, exerting outstanding therapeutic effects on ameliorating the mortality, reducing the infarct volume, and protecting neurogenic functions of neurons.

DNAzyme-Functionalized Nanomaterials: Recent Preparation, Current Applications, and Future Challenges

DNAzyme-nanomaterial bioconjugates are a popular hybrid and have received major attention for diverse biomedical applications, such as bioimaging, biosensor development, cancer therapy, and drug delivery. Therefore, significant efforts are made to develop different strategies for the preparation of inorganic and organic nanoparticles (NPs) with specific morphologies and properties. DNAzymes functionalized with metal-organic frameworks (MOFs), gold nanoparticles (AuNPs), graphene oxide (GO), and molybdenum disulfide (MoS₂ ) are introduced and summarized in detail in this review. Moreover, the focus is on representative examples of applications of DNAzyme-nanomaterials over recent years, especially in bioimaging, biosensing, phototherapy, and stimulation response delivery in living systems, with their several advantages and drawbacks. Finally, the perspective regarding the future directions of research addressing these challenges is also discussed and highlighted.

Ratiometric Fluorescence Imaging of Intracellular MicroRNA with NIR-Assisted Signal Amplification by a Ru-SiO2@Polydopamine Nanoplatform

Accurate and sensitive fluorescence imaging of intracellular miRNA is essential for understanding the mechanism underlying some physiological and pathological events, as well as the prevention and diagnosis of diseases. Herein, a highly sensitive ratiometric fluorescent nanoprobe for intracellular miRNA imaging was fabricated by integrating a Ru-SiO₂@polydopamine (Ru-SiO₂@PDA) nanoplatform with a near-infrared light (NIR)-assisted DNA strand displacement signal amplification strategy. The Ru-SiO₂@PDA spheres have excellent biosafety, high photothermal effect, and unique photophysical properties that can both emit a stable red fluorescence and well quench the fluorophores getting closer to them. So, when the fuel DNA and carboxyfluorescein (FAM)-labeled signal DNA are co-assembled on their outer surfaces, the FAM's green fluorescence is quenched, and a low ratiometric signal is obtained. However, in the presence of miRNA, the target displaces the signal DNA from the capture DNA, releasing the signal DNA far away from the Ru-SiO₂@PDA. Then, the green fluorescence recovers and leads to an enhanced I_green/I_red value. Under NIR light irradiation, the Ru-SiO₂@PDA increases the local temperature around the probe and triggers the release of fuel DNA, which thus recycles the target miRNA and effectively amplifies the ratiometric signal. Using A549 cells as a model, the nanoprobe realizes the highly sensitive ratiometric fluorescence imaging of miRNA let-7a, as well as its in vivo up- and down-regulation expressions. It provides a facile tool for highly sensitive and accurate intracellular miRNA detection through one-step incubation and may pave a new avenue for single-cell analysis.

Metal-Doped Polydopamine Nanoparticles for Highly Robust and Efficient DNA Adsorption and Sensing

Controlling DNA adsorption on nanomaterials is crucial for a wide range of applications in analytical and biomedical sciences. Polydopamine (PDA) is a versatile material that can be coated on nearly any surface, and thus adsorbing DNA onto PDA can be a general method for indirect DNA functionalization of surfaces. Polyvalent metal ions were reported to promote DNA adsorption on PDA nanoparticles (NPs), but previous works added the metal ions after the formation of PDA. Herein, we compared the effect of polyvalent metal ions added during the synthesis of PDA NPs (called metal-doped) with the effect of polyvalent metal ions added after the synthesis (metal-adsorbed). A series of metal ions including Ca²⁺, Zn²⁺, Ni²⁺, Fe³⁺, and Gd³⁺ were tested, and Zn²⁺ was studied in detail due to its excellent ability for promoting DNA adsorption. With 100 μM Zn²⁺, metal-doped NPs were ∼30% more efficient than metal-adsorbed NPs for DNA adsorption in buffer attributable to a higher metal loading on the surface of the metal-doped NPs. Metal leaching was negligible from the metal-doped NPs, and they showed a remarkably higher robustness than the metal-adsorbed NPs, resulting in a 20-fold higher DNA extraction efficiency from serum. Based on the desorption studies, a higher adsorption affinity for the metal-doped NPs was confirmed. Finally, the Zn²⁺-doped PDA NPs were used for sensitive DNA detection with a limit of detection of 0.45 nM, and the sensor was highly resistant to nonspecific protein and phosphate displacement.

A new strategy for the development of efficient impedimetric tobramycin aptasensors with metallo-covalent organic frameworks (MCOFs)

Two bimetallic CoNi-based metallo-covalent organic frameworks (MCOFs) were prepared and explored as the sensitive platforms of impedimetric aptasensors for efficient detection of tobramycin (TOB). The two CoNi-MCOFs were constructed using metallophthalocyanine tetra-amine (MPc-TA, M = Co²⁺ or Ni²⁺) and 4,4'-(1,10-phen-anthroline-2,9-diyl) dibenzaldehyde (PTD) as building units and further coordinating to the secondary metal ions (Ni²⁺ or Co²⁺) by phenanthroline. Interestingly, the immobilization ability of CoPc-TA-PTD(Ni) to TOB-targeted aptamer is higher than that of NiPc-TA-PTD(Co) due to its stronger binding interactions to aptamer. As a result, the CoPc-TA-PTD(Ni)-based aptasensor shows the superior TOB detection ability, giving a low detection limit of 0.07 fg mL^-1 and satisfied sensing performances, such as high selectivity, good reproducibility, and excellent stability. Also, the aptasensor shows the acceptable applicability for detecting TOB in milk or chicken egg. This MCOFs-based sensing strategy could be extensively applied to detect other analytes by anchoring the corresponding probes.

Phenolic-enabled nanotechnology: versatile particle engineering for biomedicine

Phenolics are ubiquitous in nature and have gained immense research attention because of their unique physiochemical properties and widespread industrial use. In recent decades, their accessibility, versatile reactivity, and relative biocompatibility have catalysed research in phenolic-enabled nanotechnology (PEN) particularly for biomedical applications which have been a major benefactor of this emergence, as largely demonstrated by polydopamine and polyphenols. Therefore, it is imperative to overveiw the fundamental mechanisms and synthetic strategies of PEN for state-of-the-art biomedical applications and provide a timely and comprehensive summary. In this review, we will focus on the principles and strategies involved in PEN and summarize the use of the PEN synthetic toolkit for particle engineering and the bottom-up synthesis of nanohybrid materials. Specifically, we will discuss the attractive forces between phenolics and complementary structural motifs in confined particle systems to synthesize high-quality products with controllable size, shape, composition, as well as surface chemistry and function. Additionally, phenolic's numerous applications in biosensing, bioimaging, and disease treatment will be highlighted. This review aims to provide guidelines for new scientists in the field and serve as an up-to-date compilation of what has been achieved in this area, while offering expert perspectives on PEN's use in translational research.

Spherical Nucleic Acid Mediated Functionalization of Polydopamine-Coated Nanoparticles for Selective DNA Extraction and Detection

Magnetic nanoparticles have been widely used for the separation of biomolecules for biological applications due to the mild and efficient separation process. In previous studies, core-shell magnetic nanoparticles (NPs) were designed for DNA extraction without much sequence specificity. In this work, to achieve highly selective DNA extraction, we designed a core-shell magnetic structure by coating polydopamine (PDA) on Fe₃O₄ NPs. Without divalent metal ions, PDA does not adsorb DNA at neutral pH. The Fe₃O₄@PDA NPs were then functionalized with spherical nucleic acids (SNA) to provide a high density of probe DNA. Fe₃O₄@PDA@SNA was also compared with when a linear SH-DNA was covalently attached to the NPs surface, showing a higher density of the probe SNA than SH-DNA can be loaded on the NPs in a remarkably shorter time. Nonspecific DNA extraction was thoroughly inhibited by both probes. DNA extraction by the Fe₃O₄@PDA@SNA was more effective as well as 5-fold faster than by the Fe₃O₄@PDA@SH-DNA, probably due to the favorable standing conformation of DNA strands in SNA. Moreover, extraction by Fe₃O₄@PDA@SNA showed high robustness in fetal bovine serum, and the same design can be used for selective detection of DNA. Finally, the method was also demonstrated on silica NPs and WS₂ nanosheets for coating with PDA and SNA. Altogether, our findings revealed an interesting and general surface modification strategy using PDA@SNA conjugates for sequence-specific DNA extraction.

Preservation of DNA for data storage

The preservation of DNA has attracted significant interest of scientists in diverse research fields from ancient biological remains to the information field. In light of the different DNA safekeeping requirements (e.g., storage time, storage conditions) in these disparate fields, scientists have proposed distinct methods to maintain the DNA integrity. Specifically, DNA data storage is an emerging research, which means that the binary digital information is converted to the sequences of nucleotides leading to dense and durable data storage in the form of synthesized DNA. The intact preservation of DNA plays a significant role because it is closely related to data integrity. This review discusses DNA preservation methods, aiming to confirm an appropriate one for synthetic oligonucleotides in DNA data storage. First, we analyze the impact factors of the DNA long-term storage, including the intrinsic stability of DNA, environmental factors, and storage methods. Then, the benefits and disadvantages of diverse conservation approaches (e.g., encapsulation-free, chemical encapsulation) are discussed. Finally, we provide advice for storing non-genetic information in DNA in vitro. We expect these preservation suggestions to promote further research that may extend the DNA storage time.

The bibliography includes 99 references.

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.

Cooperative Metal Ion-Mediated Adsorption of Spherical Nucleic Acids with a Large Hysteresis

Spherical nucleic acids (SNA) refer to nanoparticles attached with a high density of oligonuleotides. Linear and spherical nucleic acids have many differences such as hybridization affinity, melting transition, and cellular uptake. In this work, these two types of DNA of the same sequence were compared for adsorption on polydopamine (PDA) nanoparticles and graphene oxide (GO). We focused on the effect of metal ions including Na⁺, Ca²⁺, and Zn²⁺ since metal ions are indispensible for DNA adsorption on PDA and GO. Gold nanoparticles (AuNPs) of various sizes were used to prepare the SNAs. For both PDA and GO, a normal binding curve of one metal ion was obtained for adsorbing the linear DNA, while the spherical DNAs larger than 5 nm showed a sigmoidal binding curve requiring multiple metal ions. Urea and EDTA were used to probe DNA adsorption affinity, where the spherical DNA showed stronger adsorption in general. In the presence of 300 mM Na⁺, 4 M urea or 4 mM EDTA failed to desorb the 13 nm spherical DNA. The spherical DNA showed a very large hysteresis of metal-dependent adsorption. This study demonstrates another unique property of SNA compared to linear DNA, revealing interesting orientation and packing of DNA on AuNPs, which has deepened our understanding of DNA interface chemistry.

Promoting DNA Adsorption by Acids and Polyvalent Cations: Beyond Charge Screening

Adsorbing DNA oligonucleotides onto nanoparticles is the first step in developing DNA-based biosensors, drug delivery systems, and smart materials. Since DNA is a polyanion, it is repelled by negatively charged nanoparticles, which constitute the majority of commonly used nanomaterials. Adding salt such as NaCl to screen charge repulsion is a standard method of promoting DNA adsorption. However, Na⁺ does not supply additional attractive forces. In addition, adding a high concentration of NaCl can cause the aggregation of nanomaterials. In this feature article, we mainly summarize the methods developed in our laboratory to promote DNA adsorption by lowering the pH and by adding polyvalent metal ions, especially transition-metal ions. Various materials including noble metals (gold, silver, and platinum), 2D materials (graphene oxide, MoS₂, WS₂, and MXene), polydopamine, and several metal oxides are discussed. In general, low pH can protonate DNA bases and nanoparticle surfaces, reducing charge repulsion and even leading to attraction, although DNA folding at low pH can sometimes be detrimental to adsorption. Polyvalent metal ions can bridge additional interactions to achieve otherwise impossible adsorption. On the basis of the current understanding, a few future research directions are proposed to further improve DNA adsorption.