A "peptide-target-aptamer" electrochemical biosensor for norovirus detection using a black phosphorous nanosheet@Ti3C2-Mxene nanohybrid and magnetic covalent organic framework.

Norovirus (NoV) is a major foodborne pathogen responsible for acute gastroenteritis epidemics, and establishing a robust detection method for the timely identification and monitoring of NoV contamination is of great significance. In this study, a peptide-target-aptamer sandwich electrochemical biosensor for NoV was fabricated using Au@BP@Ti3C2-MXene and magnetic Au@ZnFe2O4@COF nanocomposites. The response currents of the electrochemical biosensor were proportional to the NoV concentrations ranging from 0.01-105 copies/mL with a detection limit (LOD) of 0.003 copies/mL (S/N = 3). To our best knowledge, this LOD was the lowest among published assays to date, due to the specific recognition of the affinity peptide and aptamer for NoV and the outstanding catalytic activity of nanomaterials. Furthermore, the biosensor showed excellent selectivity, anti-interference performance, and satisfactory stability. The NoV concentrations in simulative food matrixes were successfully detected using the constructed biosensor. Meanwhile, NoV in stool samples was also successfully quantified without complex pretreatment. The designed biosensor had the potential to detect NoV (even at a low level) in foods, clinical samples, and environmental samples, providing a new method for NoV detection in food safety and diagnosing foodborne pathogens.

Systematic Investigation of Tether Length and Phosphorus Configuration in Backbone Constrained Macrocyclic Nucleic Acids to Modulate Binding Kinetics for RNA.

We recently described a chemical strategy to pre-organize a trinucleotide subunit in a conformation suitable for Watson-Crick base pairing for modulating the binding kinetics of single-stranded oligonucleotides (ONs) using bis-phosphonate esters bridging hydrocarbon tethers to provide 11- and 15-membered macrocyclic analogues. In this manuscript, we describe the synthesis of all eight P-stereoisomers of macrocyclic 12-, 13-, 14-, and 16-membered hydrocarbon-bridged nucleotide trimers, their incorporation into ONs, and biophysical characterization of the modified ONs. The size of the macrocyclic tether and configuration at phosphorus had profound effects on hybridization kinetics. ONs containing 12- and 13-membered rings exhibited faster on-rates (up to 5-fold) and off-rates (up to 161-fold). In contrast, ONs using the larger ring size macrocycles generally exhibited smaller changes in binding kinetics relative to unmodified DNA. Interestingly, several of the analogues retained significant binding affinity for RNA based on their dissociation constants, despite being modestly destabilizing in the thermal denaturation experiments, highlighting the potential utility of measuring dissociation constants versus duplex thermal stability when evaluating novel nucleic acid analogues. Overall, our results provide additional insights into the ability of backbone-constrained macrocyclic nucleic acid analogues to modulate hybridization kinetics of modified ONs with RNA.

Magnetic Relaxation Switch Sensor Based on Magnetophoresis and "T-Hg(II)-T" Signal Amplification.

In this study, we designed a magnetic relaxation switch (MRS) sensor combined with magnetophoresis technology (MS-MRS), which helps solve the problems of traditional MRS sensors. The sensor is based on a new combined magnet and is composed of small magnetic blocks and iron sheets that can rapidly separate magnetic nanoparticles of different sizes within 5 min. The MS-MRS sensor consists of aptamer-functionalized magnetic nanoparticles (diameter: 200 nm) (MNP200-Apt), complementary DNA-functionalized magnetic nanoparticles (diameter: 20 nm) (MNP20-cDNA), and a combined magnet ("M2" magnet). The MNP200-Apt probe could be separated by an "M2" magnet but the MNP20-cDNA probe could not. To further improve the sensitivity of the sensor, we successfully constructed an MS-MRS-Hg sensor based on the "T-Hg(II)-T" specific recognition that aggregated MNP20-cDNA probes to amplify the relaxation signal. The detection working range of the MS-MRS sensor is 0.5-100 ng/mL and that of the MS-MRS-Hg sensor is 0.05-100 ng/mL. Their limit of detection (LOD) values are 0.15 and 0.01 ng/mL, respectively. The relative recoveries of the MS-MRS and MS-MRS-Hg sensors are 95.2-119.5% and 93.1-113.1%, respectively. These results indicate that the proposed sensors have a high accuracy level.

Oligonucleotides containing abasic threoninol-terpyridine residues as potential artificial ribonucleases.

Artificial ribonucleases, also known as synthetic ribozymes, were synthesized with an internal, stereochemically-pure, abasic threoninol backbone-residue to which the RNA transesterification catalyst copper (II) terpyridine was covalently linked. These oligonucleotide conjugates were constructed to determine if the stereochemistry of the abasic threoninol backbone residue influences the transesterification rate of complementary RNA oligonucleotides. Following synthesis, these compounds were reacted with complementary 28-mer and 159-mer RNA substrates and their relative transesterification efficiencies were determined. The transesterification kinetics were also compared with previously synthesized oligonucleotides that incorporated copper (II) terpyridine via a serinol-residue. It was determined that oligonucleotides that contained copper (II) terpyridine linked via a (2S,3S)-threoninol backbone were more efficient at RNA transesterification than their (2R,3R)-stereoisomer counterpart.

Effective silencing of miR-126 after ischemic stroke by means of intravenous α-tocopherol-conjugated heteroduplex oligonucleotide in mice.

Brain endothelial cells (BECs) are involved in the pathogenesis of ischemic stroke. Recently, several microRNAs (miRNAs) in BECs were reported to regulate the endothelial function in ischemic brain. Therefore, modulation of miRNAs in BECs by a therapeutic oligonucleotide to inhibit miRNA (antimiR) could be a useful strategy for treating ischemic stroke. However, few attempts have been made to achieve this strategy via systemic route due to lack of efficient delivery-method toward BECs. Here, we have developed a new technology for delivering an antimiR into BECs and silencing miRNAs in BECs, using a mouse ischemic stroke model. We designed a heteroduplex oligonucleotide, comprising an antimiR against miRNA-126 (miR-126) known as the endothelial-specific miRNA and its complementary RNA, conjugated to α-tocopherol as a delivery ligand (Toc-HDO targeting miR-126). Intravenous administration of Toc-HDO targeting miR-126 remarkably suppressed miR-126 expression in ischemic brain of the model mice. In addition, we showed that Toc-HDO targeting miR-126 was delivered into BECs more efficiently than the parent antimiR in ischemic brain, and that it was delivered more effectively in ischemic brain than non-ischemic brain of this model mice. Our study highlights the potential of this technology as a new clinical therapeutic option for ischemic stroke.

The interplay between a GC-rich oligonucleotide and copper ions on prion protein conformational and phase transitions.

The prion protein (PrP) misfolding to its infectious form is critical to the development of prion diseases, whereby various ligands are suggested to participate, such as copper and nucleic acids (NA). The PrP globular domain was shown to undergo NA-driven liquid-liquid phase separation (LLPS); this latter may precede pathological aggregation. Since Cu(II) is a physiological ligand of PrP, we argue whether it modulates phase separation altogether with nucleic acids. Using recombinant PrP, we investigate the effects of Cu(II) (at 6 M equivalents) and a previously described PrP-binding GC-rich DNA (equimolarly to protein) on PrP conformation, oligomerization, and phase transitions using a range of biophysical techniques. Raman spectroscopy data reveals the formation of the ternary complex. Microscopy suggests that phase separation is mainly driven by DNA, whereas Cu(II) has no influence. Our results show that DNA can be an adjuvant, leading to the structural conversion of PrP, even in the presence of an endogenous ligand, copper. These results provide new insights into the role of Cu(II) and NA on the phase separation, structural conversion, and aggregation of PrP, which are critical events leading to neurodegeneration.

Oligonucleotide-capped nanoporous anodic alumina biosensor as diagnostic tool for rapid and accurate detection of Candida auris in clinical samples.

Candida auris has arisen as an important multidrug-resistant fungus because of several nosocomial outbreaks and elevated rates of mortality. Accurate and rapid diagnosis of C. auris is highly desired; nevertheless, current methods often present severe limitations and produce misidentification. Herein a sensitive, selective, and time-competitive biosensor based on oligonucleotide-gated nanomaterials for effective detection of C. auris is presented. In the proposed design, a nanoporous anodic alumina scaffold is filled with the fluorescent indicator rhodamine B and the pores blocked with different oligonucleotides capable of specifically recognize C. auris genomic DNA. Gate opening modulation and cargo delivery is controlled by successful DNA recognition. C. auris is detected at a concentration as low as 6 CFU/mL allowing obtaining a diagnostic result in clinical samples in one hour with no prior DNA extraction or amplification steps.

Polystyrene Microparticles with Convergently Grown Mesoporous Silica Shells as a Promising Tool for Multiplexed Bioanalytical Assays.

Functional core/shell particles are highly sought after in analytical chemistry, especially in methods suitable for single-particle analysis such as flow cytometry because they allow for facile multiplexed detection of several analytes in a single run. Aiming to develop a powerful bead platform of which the core particle can be doped in a straightforward manner while the shell offers the highest possible sensitivity when functionalized with (bio)chemical binders, polystyrene particles were coated with different kinds of mesoporous silica shells in a convergent growth approach. Mesoporous shells allow us to obtain distinctly higher surface areas in comparison with conventional nonporous shells. While assessing the potential of narrow- as well as wide-pore silicas such as Mobil composition of matter no. 41 (MCM-41) and Santa Barbara amorphous material no. 15 (SBA-15), especially the synthesis of the latter shells that are much more suitable for biomolecule anchoring was optimized by altering the pH and both, the amount and type of the mediator salt. Our studies showed that the best performing material resulted from a synthesis using neutral conditions and MgSO4 as an ionic mediator. The analytical potential of the particles was investigated in flow cytometric DNA assays after their respective functionalization for individual and multiplexed detection of short oligonucleotide strands. These experiments revealed that a two-step modification of the silica surface with amino silane and succinic anhydride prior to coupling of an amino-terminated capture DNA (c-DNA) strand is superior to coupling carboxylic acid-terminated c-DNA to aminated core/shell particles, yielding limits of detection (LOD) down to 5 pM for a hybridization assay, using labeled complementary single-stranded target DNA (t-DNA) 15mers. The potential of the use of the particles in multiplexed analysis was shown with the aid of dye-doped core particles carrying a respective SBA-15 shell. Characteristic genomic sequences of human papillomaviruses (HPV) were chosen as the t-DNA analytes here, since their high relevance as carcinogens and the high number of different pathogens is a relevant model case. The title particles showed a promising performance and allowed us to unequivocally detect the different high- and low-risk HPV types in a single experimental run.

Hairpin-Bisulfite PCR.

Ligation of a hairpin oligonucleotide to genomic DNA prior to bisulfite conversion and PCR amplification physically links the two complementary DNA strands. This additional step in the conversion procedure overcomes the limitations of conventional bisulfite sequencing where information of the cytosine methylation status is only obtained from one of the two strands of an individual DNA molecule. Sequences derived from hairpin bisulfite PCR products reveal the dynamics of this epigenetic memory system on both strands of individual DNA molecules. The chapter describes a reliable step-by-step procedure to generate hairpin-linked DNA. It also provides a guide for efficient bisulfite conversion that is suitable for both conventional and hairpin bisulfite sequencing approaches.

Ester modification at the 3' end of anti-microRNA oligonucleotides increases potency of microRNA inhibition.

MicroRNAs (miRNAs) are short noncoding RNAs that play a fundamental role in gene regulation. Deregulation of miRNA expression has a strong correlation with disease and antisense oligonucleotides that bind and inhibit miRNAs associated with disease have therapeutic potential. Current research on the chemical modification of anti-miRNA oligonucleotides (anti-miRs) is focused on alterations of the phosphodiester-ribose backbone to improve nuclease resistance and binding affinity to miRNA strands. Here we describe a structure-guided approach for modification of the 3'-end of anti-miRs by screening for modifications compatible with a nucleotide-binding pocket present on human Argonaute2 (hAgo2). We computationally screened a library of 190 triazole-modified nucleoside analogs for complementarity to the t1A-binding pocket of hAgo2. Seventeen top scoring triazoles were then incorporated into the 3' end of anti-miR21 and potency was evaluated for each in a cell-based assay for anti-miR activity. Four triazole-modified anti-miRs showed higher potency than anti-miR21 bearing a 3' adenosine. In particular, a triazole-modified nucleoside bearing an ester substituent imparted a nine-fold and five-fold increase in activity for both anti-miR21 and anti-miR122 at 300 and 5 nM, respectively. The ester group was shown to be critical as a similar carboxylic acid and amide were inactive. Furthermore, anti-miR 3' end modification with triazole-modified nucleoside analogs improved resistance to snake venom phosphodiesterase, a 3'-exonuclease. Thus, the modifications described here are good candidates for improvement of anti-miR activity.

Terminal Mono- and Bis-Conjugates of Oligonucleotides with Closo-Dodecaborate: Synthesis and Physico-Chemical Properties.

Oligonucleotide conjugates with boron clusters have found applications in different fields of molecular biology, biotechnology, and biomedicine as potential agents for boron neutron capture therapy, siRNA components, and antisense agents. Particularly, the closo-dodecaborate anion represents a high-boron-containing residue with remarkable chemical stability and low toxicity, and is suitable for the engineering of different constructs for biomedicine and molecular biology. In the present work, we synthesized novel oligonucleotide conjugates of closo-dodecaborate attached to the 5'-, 3'-, or both terminal positions of DNA, RNA, 2'-O-Me RNA, and 2'-F-Py RNA oligomers. For their synthesis, we employed click reaction with the azido derivative of closo-dodecaborate. The key physicochemical characteristics of the conjugates have been investigated using high-performance liquid chromatography, gel electrophoresis, UV thermal melting, and circular dichroism spectroscopy. Incorporation of closo-dodecaborate residues at the 3'-end of all oligomers stabilized their complementary complexes, whereas analogous 5'-modification decreased duplex stability. Two boron clusters attached to the opposite ends of the oligomer only slightly influence the stability of complementary complexes of RNA oligonucleotide and its 2'-O-methyl and 2'-fluoro analogs. On the contrary, the same modification of DNA oligonucleotides significantly destabilized the DNA/DNA duplex but gave a strong stabilization of the duplex with an RNA target. According to circular dichroism spectroscopy results, two terminal closo-dodecaborate residues cause a prominent structural rearrangement of complementary complexes with a substantial shift from the B-form to the A-form of the double helix. The revealed changes of key characteristics of oligonucleotides caused by incorporation of terminal boron clusters, such as the increase of hydrophobicity, change of duplex stability, and prominent structural changes for DNA conjugates, should be taken into account for the development of antisense oligonucleotides, siRNAs, or aptamers bearing boron clusters. These features may also be used for engineering of developing NA constructs with pre-defined properties.

DNA Analogues Modified at the Nonlinking Positions of Phosphorus.

Chemically modified oligonucleotides are being developed as a new class of medicines for curing conditions that previously remained untreatable. Three primary classes of therapeutic oligonucleotides are single-stranded antisense oligonucleotides (ASOs), double stranded small interfering RNAs (siRNAs), and oligonucleotides that induce exon skipping. Recently, ASOs, siRNAs, and exon skipping oligonucleotides have been approved for patients with unmet medical needs, and many other candidates are being tested in late stage clinical trials. In coming years, therapeutic oligonucleotides may match the promise of small molecules and antibodies. Interestingly, in the 1980s when we developed chemical methods for synthesizing oligonucleotides, no one would have imagined that these highly charged macromolecules could become future medicines. Indeed, the anionic nature and poor metabolic stability of the natural phosphodiester backbone provided a major challenge for the use of oligonucleotides as therapeutic drugs. Thus, chemical modifications of oligonucleotides were essential in order to improve their pharmacokinetic properties. Keeping this view in mind, my laboratory has developed a series of novel oligonucleotides where one or both nonbridging oxygens in the phosphodiester backbone are replaced with an atom or molecule that introduces molecular properties that enhance biological activity. We followed two complementary approaches. One was the use of phosphoramidites that could act directly as synthons for the solid phase synthesis of oligonucleotide analogues. This approach sometimes was not feasible due to instability of various synthons toward the reagents used during synthesis of oligonucleotides. Therefore, using a complementary approach, we developed phosphoramidite synthons that can be incorporated into oligonucleotides with minimum changes in the solid phase DNA synthesis protocols but contain a handle for generating appropriate analogues postsynthetically.This Account summarizes our efforts toward preparing these types of analogues over the past three decades and discusses synthesis and properties of backbone modified oligonucleotides that originated from the Caruthers' laboratory. For example, by replacing one of the internucleotide oxygens with an acetate group, we obtained so-called phosphonoacetate oligonucleotides that were stable to nucleases and, when delivered as esters, entered into cells unaided. Alternatively oligonucleotides bearing borane phosphonate linkages were found to be RNase H active and compatible with the endogenous RNA induced silencing complex (RISC). Oligonucleotides containing an alkyne group directly linked to phosphorus in the backbone were prepared as well and used to attach molecules such as amino acids and peptides.

Phosphorus Dendrimers as Nanotools against Cancers.

This review concerns the use of dendrimers, especially of phosphorhydrazone dendrimers, against cancers. After the introduction, the review is organized in three main topics, depending on the role played by the phosphorus dendrimers against cancers: (i) as drugs by themselves; (ii) as carriers of drugs; and (iii) as indirect inducer of cancerous cell death. In the first part, two main types of phosphorus dendrimers are considered: those functionalized on the surface by diverse organic derivatives, including known drugs, and those functionalized by diverse metal complexes. The second part will display the role of dendrimers as carriers of anticancer "drugs", which can be either small molecules or anticancer siRNAs, or the combination of both. In the third part are gathered a few examples of phosphorhydrazone dendrimers that are not cytotoxic by themselves, but which under certain circumstances induce a cytotoxic effect on cancerous cells. These examples include a positive influence on the human immune system and the combination of bioimaging with photodynamic therapy properties.

Delivery of Oligonucleotides to the Liver with GalNAc: From Research to Registered Therapeutic Drug.

Targeted delivery of oligonucleotides to liver hepatocytes using N-acetylgalactosamine (GalNAc) conjugates that bind to the asialoglycoprotein receptor has become a breakthrough approach in the therapeutic oligonucleotide field. This technology has led to the approval of givosiran for the treatment of acute hepatic porphyria, and there are another seven conjugates in registrational review or phase 3 trials and at least another 21 conjugates at earlier stages of clinical development. This review highlights some of the recent chemical and preclinical advances in this space, leading to a large number of clinical candidates against a diverse range of targets in liver hepatocytes. The review focuses on the use of this delivery system for small interfering RNAs (siRNAs) and antisense molecules that cause downregulation of target mRNA and protein. A number of other approaches such as anti-microRNAs and small activating RNAs are starting to exploit the technology, broadening the potential of this approach for therapeutic oligonucleotide intervention.

Technical Considerations for Use of Oligonucleotide Solution API.

The most common approach for the manufacture of oligonucleotides includes isolation of the active pharmaceutical ingredient (API) via lyophilization to provide a solid product, which is then dissolved to provide an aqueous formulation. It is well known from the development and manufacture of large molecules ("biologics") that API production does not always require isolation of solid API before drug product formulation, and this article provides technical considerations for the analogous use of oligonucleotide API in solution. The primary factor considered is solution stability, and additional factors such as viscosity, concentration, end-to-end manufacturing, microbiological control, packaging, and storage are also discussed. The technical considerations discussed in this article will aid the careful evaluation of the relative advantages and disadvantages of solution versus powder API for a given oligonucleotide drug substance.

Tumor-Targeted Drug and CpG Delivery System for Phototherapy and Docetaxel-Enhanced Immunotherapy with Polarization toward M1-Type Macrophages on Triple Negative Breast Cancers.

Cancer immunotherapy has achieved promising clinical responses in recent years owing to the potential of controlling metastatic disease. However, there is a limited research to prove the superior therapeutic efficacy of immunotherapy on breast cancer compared with melanoma and non-small-cell lung cancer because of its limited expression of PD-L1, low infiltration of cytotoxic T lymphocytes (CTLs), and high level of myeloid-derived suppressor cells (MDSCs). Herein, a multifunctional nanoplatform (FA-CuS/DTX@PEI-PpIX-CpG nanocomposites, denoted as FA-CD@PP-CpG) for synergistic phototherapy (photodynamic therapy (PDT), photothermal therapy (PTT) included) and docetaxel (DTX)-enhanced immunotherapy is successfully developed. The nanocomposites exhibit excellent PDT efficacy and photothermal conversion capability under 650 and 808 nm irradiation, respectively. More significantly, FA-CD@PP-CpG with no obvious side effects can remarkably inhibit the tumor growth in vivo based on a 4T1-tumor-bearing mice modal. A low dosage of loaded DTX in FA-CD@PP-CpG can promote infiltration of CTLs to improve efficacy of anti-PD-L1 antibody (aPD-L1), suppress MDSCs, and effectively polarize MDSCs toward M1 phenotype to reduce tumor burden, further to enhance the antitumor efficacy. Taken together, FA-CD@PP-CpG nanocomposites offer an efficient synergistic therapeutic modality in docetaxel-enhanced immunotherapy for clinical application of breast cancer.

Duplex-forming Oligonucleotide of Triazole-linked RNA.

An oligonucleotide of triazole-linked RNA (TL RNA) was synthesized by performing consecutive copper-catalyzed azide-alkyne cycloaddition reactions for elongation. The reaction conditions that had been optimized for the synthesis of 3-mer TL RNA were found to be inappropriate for longer oligonucleotides, and the conditions were reoptimized for the solid-phase synthesis of an 11-mer TL RNA oligonucleotide. Duplex formation of the 11-mer TL RNA oligonucleotide was examined with the complementary oligonucleotide of natural RNA to reveal the effects of the 2'-OH groups on the duplex stability.

A three-dimensional (3D) printed biomimetic hierarchical scaffold with a covalent modular release system for osteogenesis.

Hydroxyapatite (HA) ceramics are well known for their biocompatibility, bioactivity, and osteoconductive nature. However, limited hierarchical structure and lack of ease in modularity hinder the widespread application of conventional HA ceramics. By using three-dimensional printing (3DP) techniques with multiple materials, including HA, complex biological and mechanical architecture of natural organisms can be achieved through biomimetics. In this study, we designed an osteoid, biomimetic, hierarchical, porous HA ceramic 3D printed scaffold (3DPs). Further incorporation of a covalent, modular, controlled release system (CMR), based on Watson-Crick's complementary oligonucleotides, and was added to carry a bone morphogenetic protein-2 (BMP2) peptide. The choice of a HA biomimetic scaffold housing BMP2 protein fragments was selected to successfully promote osteogenesis both in vitro and in vivo. Scanning electron microscopy, micro-computed tomography analysis and computer fluid dynamics simulations of the 3DPs showed a uniform biomimetic hierarchical structure and an effective interior permeability. Active molecules were found bound with high stability and modular to the scaffold surface via the CMR system. After 7 days of incubation under physiological conditions, approximately 90% of active factors remained bound. Compared to control groups, the 3DPs-CMR-BMP2 group significantly enhanced cell proliferation and adhesion. Moreover, the 3DPs-CMR-BMP2 group exhibited more extensive and sustained osteogenic effects through upregulated expression of osteogenic factors and enhanced calcium deposition, as compared to study and control groups. Furthermore, ectopic osteogenesis and a critical calvarial defect model confirmed that the 3DPs-CMR-BMP2 group significantly promoted in vivo bone healing versus control. Thus, our results showed that biomimetic hierarchical 3DPs with a CMR system successfully promote cell proliferation, adhesion, differentiation and osteogenesis, on a continuous cycle. The biomimetic hierarchical 3DPs with a CMR system offers a promising multi-functional, bone substitute material for treatment of patients with bone defects.

Phosphodiester photo-tethers for the (multi-)cyclic conformational caging of oligonucleotides.

The ability to address the function of oligonucleotides with light is highly desirable since they are often used experimentally in the regulation of biological processes that need to be controlled in time, space and activation level. Here we present an extension of our initial approach of using photo-tethers that force single strands of nucleic acids into a circle, thus making them unable to form a duplex with a complementary DNA- or RNA-strand. Due to the persistence length a single strand can form a circle of, for example, 30 nucleotides, but a duplex cannot. We show that these new photo-tethers can also be easily installed on the phosphodiester backbone. This simplifies the approach considerably and leads to temporarily inhibited oligonucleotides that can only form a duplex after linearization by photoactivation.

Mn2+-Assisted DNA Oligonucleotide Adsorption on Ti2C MXene Nanosheets.

As a new type of 2D nanomaterial, MXene (transition metal carbide/nitride) nanosheets are already widely used in catalysis, sensing, and energy research. DNA is a popular sensing molecule. Compared to other 2D materials such as graphene oxide, MoS2, and WS2, few fundamental studies were carried out on DNA adsorption by MXene. Due to its exfoliation and delamination process, the surface of MXene is abundant in -F, -OH, and -O- groups, rendering the surface negatively charged and repelling DNA. In previous studies, surface modification of MXene was performed to promote DNA adsorption. Herein, Mn2+ was discovered to promote DNA adsorption on unmodified Ti2C MXene. Different from Ca2+ and Mg2+, Mn2+ can inverse the ζ-potential of the Ti2C MXene to positive. DNA mainly uses its phosphate backbone for adsorption, while its bases contribute significantly less. In addition, delayed DNA desorption was observed through the addition of inorganic phosphate due to the formation of manganese phosphate to gradually extract Mn2+ from the DNA/MXene complex. Finally, DNA-induced DNA desorption from the Ti2C MXene can hardly distinguish the complementary DNA from a random DNA, which is very different from that for graphene oxide. This difference is likely due to the distinct surface chemistry between the MXene and graphene oxide.