Metal coordinated materials are attractive for many applications including catalysis, sensing, and controlled release. Adenine and its derivatives have been widely used to generate many coordination complexes, polymers, and nanoparticles. However, few of these materials display fluorescence. Herein, we report fluorescent gold complexes and nanoclusters formed with adenosine, deoxyadenosine, AMP and ATP, where the former two produced micrometer-sized particles and the latter two produced molecular clusters. Only weak fluorescence was produced with adenine, while no emission was observed with uridine, cytidine or guanosine. We found that adding citrate and light exposure are two key factors to generate fluorescence and their mechanistic roles have been explored. In all the products, the ratio between gold and adenine was determined to be 1:1 using UV-vis spectroscopy. Mass spectrometry showed clusters containing 2, 4, and 6 gold atoms in the gas phase.The fluorescence peak is around 470 nm for the AMP and ATP complex and 480 nm for the (deoxy)adenosine complexes. This work has provided a systematic approach to obtain fluorescent metal coordinated polymers and materials with tunable sizes, which will find applications in analytical chemistry, drug delivery and imaging. The fundamental physical chemistry of these materials has been systematically explored.

Titanium nitride-carbon nanotube (TiN-CNT) core-shell nanocomposites were developed by a simplistic two step fabrication procedure and characterized by transmission electron microscopy, X-ray diffraction and thermogravimetric analysis. These materials were utilized as platinum nanoparticle electrocatalyst supports (Pt/TiN-CNT) for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), two important low temperature fuel cell processes. Improved ORR and MOR activities were demonstrated for Pt/TiN-CNTs compared with state of the art commercial Pt/C. Moreover, enhanced CO tolerance towards the MOR was demonstrated attributed to the interaction occurring between adsorbed CO molecules and the TiN-CNT supports. TiN-CNTs are thus presented as highly promising, novel electrocatalyst support materials with enhanced ORR and MOR performance attributed to their anisotropic morphology, enhanced electronic properties and conductivity, and distinct catalyst-support interactions.

Interfacing DNA with liposomes has produced a diverse range of programmable soft materials, devices, and drug delivery vehicles. By simply controlling liposomal composition, bilayer fluidity, lipid domain formation, and surface charge can be systematically varied. Recent development in DNA research has produced not only sophisticated nanostructures but also new functions including ligand binding and catalysis. For noncationic liposomes, a DNA is typically covalently linked to a hydrophobic or lipid moiety that can be inserted into lipid membranes. In this article, we discuss fundamental biointerfaces formed between DNA and noncationic liposomes. The methods to prepare such conjugates and the interactions at the membrane interfaces are also discussed. The effect of DNA lateral diffusion on fluid bilayer membranes and the effect of membrane on DNA assembly are emphasized. DNA hybridization can be programmed to promote fusion of lipid membranes. Representative applications of this conjugate for drug delivery, biosensor development, and directed assembly of materials are briefly described toward the end. Some future research directions are also proposed to further understand this biointerface.

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Phosphate-containing molecules exist in many forms in biology and the environment, and their interaction with metal oxides is an important aspect of their chemistry and biochemistry. In this work, phosphates with different degrees of polymerization (e.g., orthophosphate, pyrophosphate (PPi), sodium triphosphate (STPP), sodium trimetaphosphate (STMP), and polyphosphate with 25 phosphate units) and phosphates with one or two capping groups were studied. CeO nanoparticles (nanoceria) were used as a model metal oxide. DNA is also a polyphosphate, and a fluorescently labeled DNA oligonucleotide was mixed with nanoceria. These phosphate species were individually added to displace the adsorbed DNA. Longer phosphate chains were more efficient when each molecule was used at the same molar concentration, whereas PPi and STPP were most efficient at the same total phosphorus atom concentration. By capping the phosphate with organic groups, the affinity was significantly decreased. Isothermal titration calorimetry (ITC) was also performed to quantitatively measure thermodynamic parameters. Although STMP was very slow at displacing DNA, it was still adsorbed very strongly by nanoceria from ITC, indicating kinetic effects likely due to its ring structure. This observation allowed us to use the DNA as a probe to study the hydrolysis of STMP to form STPP. In summary, this study provides a systematic understanding of phosphate species interacting with metal oxides, and interestingly, it demonstrates an analytical application as well.

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Interfacing nanomaterials with DNA has resulted in the development of numerous biosensors, optimized for different targets and applications. Of all nanomaterials, graphene oxide (GO) has emerged as a prime sensing platform due to its high specific surface area, good aqueous stability, varied functional groups and desirable surface, and electrical and optical properties. This review starts with an introduction of GO and describes its physical and chemical properties. Then, the general strategies of interfacing DNA and GO to develop sensors are discussed. The trends in GO/DNA biosensor development are organized into classes based on the mode of DNA interaction with GO (physisorbed vs chemisorbed). Due to the intermediate DNA adsorption strength on GO, most of the sensors developed utilize physisorption of DNA to GO. Even within the realm of physisorbed probes, there are multiple sensing methods: direct adsorption, inhibited adsorption, competitive adsorption with the use of blocking agents, and tethered adsorption containing a strongly adsorbing block of DNA. Covalently linked DNA probes are also used to increase the biosensor stability. Each of these sensors has its advantages and disadvantages and the designs are discussed with representative examples in detail.

With multiple metal binding sites, nucleobases, nucleosides, and nucleotides form various coordination polymers (CPs) with metal ions. These self-assembled materials are very interesting for their simplicity to prepare, highly tunable structure and properties, and excellent biocompatibility.P olymerization is achieved under ambient conditions without the need of free radical initiators or UV light. Different nucleobases have different metal-binding preferences, but in general most of their coordinations ites prefer borderline or soft metals, while the phosphate groups in the nucleotides prefer hard Lewis acids. In this Focus Review,r ecent developments in this fielda re summarized startingf rom the synthesis and characterization of these CPs. Various metal ions includingg old, silver,l anthanides, zinc, copper, and iron are individually reviewed, and each metal brings its own property into the CP materials.While mostoft hese materials are non-crystalline nanoparticles, under certainc onditions crystalline metal-organic frameworks (MOFs) andh ydrogels can also be prepared. The applicationso fs uch CPs are then described including enzyme entrapment,d rug loading and delivery, biosensor development, catalysis, coating of nanoparticles, and luminescence. Finally,f uture research opportunities of this field are discussed.