A novel dual-activatable fluorescence/MRI bimodal platform is designed for tumor cell imaging by using a redoxable manganese dioxide (MnO2) nanosheet-aptamer nanoprobe. The redoxable MnO2 nanosheet acts as a DNA nanocarrier, fluorescence quencher, and intracellular glutathione (GSH)-activated MRI contrast agent. In the absence of target cells, neither fluorescence signaling nor MRI contrast of the nanoprobe is activated. In the presence of target cells, the binding of aptamers to their targets weakens the adsorption of aptamers on the MnO2 nanosheets, causing partial fluorescence recovery, illuminating the target cells, and also facilitating the endocytosis of nanoprobes into target cells. After endocytosis, the reduction of MnO2 nanosheets by GSH further activates the fluorescence signals and generates large amounts of Mn(2+) ions suitable for MRI. This platform should facilitate the development of various dual-activatable fluorescence/MRI bimodalities for use in cells or in vivo.

ConspectusDNA performs a vital function as a carrier of genetic code, but in the field of nanotechnology, DNA molecules can catalyze chemical reactions in the cell, that is, DNAzymes, or bind with target-specific ligands, that is, aptamers. These functional DNAs with different modifications have been developed for sensing, imaging, and therapeutic systems. Thus, functional DNAs hold great promise for future applications in nanotechnology and bioanalysis. However, these functional DNAs face challenges, especially in the field of biomedicine. For example, functional DNAs typically require the use of cationic transfection reagents to realize cellular uptake. Such reagents enter the cells, increasing the difficulty of performing bioassays in vivo and potentially damaging the cell’s nucleus. To address this obstacle, nanomaterials, such as metallic, carbon, silica, or magnetic materials, have been utilized as DNA carriers or assistants. In this Account, we describe selected examples of functional DNA-containing nanomaterials and their applications from our recent research and those of others. As models, we have chosen to highlight DNA/nanomaterial complexes consisting of gold nanoparticles, graphene oxides, and aptamer–micelles, and we illustrate the potential of such complexes in biosensing, imaging, and medical diagnostics.Under proper conditions, multiple ligand–receptor interactions, decreased steric hindrance, and increased surface roughness can be achieved from a high density of DNA that is bound to the surface of nanomaterials, resulting in a higher affinity for complementary DNA and other targets. In addition, this high density of DNA causes a high local salt concentration and negative charge density, which can prevent DNA degradation. For example, DNAzymes assembled on gold nanoparticles can effectively catalyze chemical reactions even in living cells. And it has been confirmed that DNA–nanomaterial complexes can enter cells more easily than free single-stranded DNA.Nanomaterials can be designed and synthesized in needed sizes and shapes, and they possess unique chemical and physical properties, which make them useful as DNA carriers or assistants, excellent signal reporters, transducers, and amplifiers. When nanomaterials are combined with functional DNAs to create novel assay platforms, highly sensitive biosensing and high-resolution imaging result. For example, gold nanoparticles and graphene oxides can quench fluorescence efficiently to achieve low background and effectively increase the signal-to-background ratio. Meanwhile, gold nanoparticles themselves can be colorimetric reporters because of their different optical absorptions between monodispersion and aggregation.DNA self-assembled nanomaterials contain several properties of both DNA and nanomaterials. Compared with DNA–nanomaterial complexes, DNA self-assembled nanomaterials more closely resemble living beings, and therefore they have lower cytotoxicity at high concentrations. Functional DNA self-assemblies also have high density of DNA for multiva...

We report the design of a self-assembled aptamer-micelle nanostructure that achieves selective and strong binding of otherwise low-affinity aptamers at physiological conditions. Specific recognition ability is directly built into the nanostructures. The attachment of a lipid tail onto the end of nucleic acid aptamers provides these unique nanostructures with an internalization pathway. Other merits include: extremely low off rate once bound with target cells, rapid recognition ability with enhanced sensitivity, low critical micelle concentration values, and dual-drug delivery pathways. To prove the potential detection/delivery application of this aptamer-micelle in biological living systems, we mimicked a tumor site in the blood stream by immobilizing tumor cells onto the surface of a flow channel device. Flushing the aptamer-micelles through the channel demonstrated their selective recognition ability under flow circulation in human whole-blood sample. The aptamermicelles show great dynamic specificity in flow channel systems that mimic drug delivery in the blood system. Therefore, our DNA aptamer-micelle assembly has shown high potential for cancer cell recognition and for in vivo drug delivery applications.DNA aptamers | drug delivery | micelles | molecular specificity M any interesting nanomaterials, either natural or artificial, have been designed to perform unique functions through the process of molecular self-assembly. In nature, the apoptosome (1) is one such example. Individual apaf-1 protein does not have a biological function; however, when forming a complex with cytochrome-c, several individual proteins self-assemble into a wheel structure called an apoptosome. Once formed, the apoptosome can then recruit and activate the otherwise inactive procaspase-9 that can then activate other caspases and trigger a cascade of events leading to apoptosis. Learning from nature, chemists have created various artificial nanostructures. Micelle is one of such examples. Polymeric micelles have been subjected to extensive studies in the field of drug delivery, functioning as drug solibilizers and carriers (2). More recently, a micelle constructed as a hybrid from hydrophilic oligonucleotide and hydrophobic polymer (3, 4) has drawn close attention. In aqueous solutions, this type of amphiphilic block copolymer can self-assemble into a three-dimensional spherical micelle structure or a nanorod-like micelle structure. This type of micelle has been shown to efficiently carry a variety of cargos to cells, including antisense oligonucleotides (5) and drug molecules (6). To perform efficient targeted delivery, folic acid, a type of cancer cell recognition molecule modified on a piece of short, complementary DNA, was clicked onto the micelles based on Watson-Crick base pairing (6).Aside from Watson-Crick base pairing, single-stranded oligonucleotides can recognize other target molecules based on noncovalent interactions, such as hydrophobic interaction and hydrogen bonding. This type of oligonucleotide ligand is known as an ...

The development of nanotechnology has been largely inspired by the biological world. The complex, but well-organized, living system hosts an array of molecular-sized machines responsible for information processing, structure building and, sometimes, movement. We present here a novel light-powered DNA mechanical device, which is reminiscent of cellular protein motors in nature, especially those of green plants. This walking device, which is based on pyrene- assisted photolysis of disulfide bonds, is capable of autonomous locomotion, with light control of initiation, termination and velocity. Based on DNA sequence design and such physical conditions as temperature and ionic strength, this photon-fueled DNA walker exhibits the type of operational freedom and mechanical speed that may rival protein motors in the future.

Aptamer–drug conjugates (ApDCs) are promising targeted drug delivery systems for reducing toxicity while increasing the efficacy of chemotherapy. However, current ApDC technologies suffer from problems caused by the complicated preparation and low controllability of drug–aptamer conjugation. To solve such problems, we have designed and synthesized a therapeutic module for solid phase synthesis, which is a phosphoramdite containing an anticancer drug moiety and a photocleavable linker. Using this module, we have realized automated and modular synthesis of ApDCs, and multiple drugs were efficiently incorporated into ApDCs at predesigned positions. The ApDCs not only recognize target cancer cells specifically, but also release drugs in a photocontrollable manner. We demonstrated the potential of automated and modular ApDC technology for applications in targeted cancer therapy.

Targeted chemotherapy and magnetic resonance imaging of cancer cells in vitro has been achieved using a smart multifunctional nanostructure (SMN) constructed from a porous hollow magnetite nanoparticle (PHMNP), a heterobifunctional PEG ligand, and an aptamer. The PHMNPs were prepared through a three-step reaction and loaded with the anticancer drug doxorubicin while being functionalized with PEG ligands. Targeting aptamers were then introduced by reaction with the PEG ligands. The pores of the PHMNPs are stable at physiological pH, but they are subject to acid etching. Specific binding and uptake of the SMN to the target cancer cells induced by aptamers was observed. In addition, multiple aptamers on the surface of one single SMN led to enhanced binding and uptake to target cancer cells due to the multivalent effect. Upon reaching the lysosomes of target cancer cells through receptor-mediated endocytosis, the relatively low lysosomal pH level resulted in corrosion of the PHMNP pores, facilitating the release of doxorubicin to kill the target cancer cells. In addition, the potential of using SMN for magnetic resonance imaging was also investigated.

Because of their facile preparation, small size (<100 nm), programmable design, and biocompatibility, lipid-based DNA micelles show enormous potential as a tool to monitor biological events and treat human diseases. However, their structural stability in biological matrices suffers from spatiotemporal variability, thus limiting their in vivo use. Herein, we have engineered stability-tunable DNA micelle flares using photocontrollable dissociation of intermolecular G-quadruplexes, which confers DNA micelle flares with robust structural stability against disruption by serum albumin. However, once exposed to light, the G-quadruplex formation is blocked by strand hybridization, resulting in the loss of stability in the presence of serum albumin and subsequent cellular uptake. This programmable regulation to stabilize lipid-based micelles in the presence of fatty-acid-binding serum albumin should further the development of biocompatible DNA micelles for in vivo applications.

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