Abstract. Cerium oxide nanoparticles (nanoceria) have recently emerged as a nanozyme with oxidase activity. In this work we present a few important interfacial properties of nanoceria. First, the surface charge of nanoceria can be controlled not only by adjusting pH but also by adsorption of simple inorganic anions. Adsorption of phosphate and citrate gives negatively charged surface over a broad pH range. Second, nanoceria adsorbs DNA via the DNA phosphate backbone in a sequence-independent manner; DNA adsorption inhibits its oxidase activity. Other anionic polymers display much weaker inhibition effects. Adsorption of simple inorganic phosphate does not have the inhibition effect. Third, nanoceria is a quencher for many fluorophores. These discoveries provide an important understanding for further use of nanoceria in biosensor development, materials science and nanotechnology.Keywords: cerium oxide, nanozymes, adsorption, surface charge, oxidaseEnzymes usually refer to protein-based biocatalysts with high activity and substrate specificity; they play crucial roles in life and are the central molecules in biochemistry, biotechnology and analytical

Developing chemical probes to distinguish each lanthanide ion is a long-standing challenge. Aside from its analytical applications, solving this problem will also enhance our knowledge in metal ligand design. Using in vitro selection, we previously reported four RNA-cleaving DNAzymes, each with a different activity trend cross the lanthanide series. We herein performed another eight in vitro selection experiments using each and every lanthanide from La 3+ to Tb 3+ but excluding the radioactive Pm 3+ . A new DNAzyme named Gd2b was identified and characterized. By labeling this DNAzyme with a fluorophore/quencher pair to create a catalytic beacon, a detection limit of 14 nM Gd 3+ was achieved. With the same beacon design, all the five lanthanide-specific DNAzymes were used together to form a sensor array. Each lanthanide ion produces a unique response pattern with these five sensors, allowing a pattern-recognition-based linear discriminant analysis (LDA) algorithm to be applied, where separation was achieved between lanthanides and nonlanthanides, light and heavy lanthanides, and for the most part, each lanthanide. These lanthanidespecific DNA molecules are useful for understanding lanthanide coordination chemistry, designing hybrid materials, and developing related analytical probes.

Using sensitized Tb 3+ luminescence spectroscopy as a tool, binding of 14 lanthanides to a lanthanide-dependent DNAzyme is studied, where the binding affinity is symmetric cross the series and the tightest binding occurs with Nd 3+ and Ho 3+ . This trend does not correlate with DNAzyme activity, suggesting that metal binding may not be the rate-limiting step of the DNAzyme catalysis.Lanthanides refer to the elements in the periodic table from La to Lu. Beyond their critical roles in modern technologies, lanthanides also emerge as important probes for biology and medicine. 1,2 In particular, they have been extensively used to study the structure and function of nucleic acids. These applications take advantage of a few of their unique properties. First, lanthanides and their complexes can efficiently cleave nucleic acids, 3 and thus are used as RNA structural probes 4 and DNA cleaving agents. 5 In addition, a number of in vitro selection experiments were carried out using lanthanides as metal cofactors to obtain DNA-based catalysts (so called DNAzymes 6-12 ) for RNA or DNA cleavage. 13,14 Second, a few lanthanides (especially Tb 3+ ) are luminescent and DNA can act as an antenna to increase their light absorption and thus emission intensity. This is useful for probing metal binding sites, 15 and for developing biosensors. 16 Third, lanthanides are hard Lewis acids and some have a similar size as Ca 2+ . Lanthanides can compete with other metal ions in enzymes and act as enzyme inhibitors. For example, both the 17E DNAzyme and the hammerhead ribozyme are inhibited by lanthanides. 15,17 On the other hand, the Leadzyme and a DNA-based ligase are accelerated by lanthanides. [18][19][20] All these examples suggest strong interactions between lanthanides and nucleic acids. Finally, nucleotides and lanthanides can form coordination complexes with useful luminescence and DNA binding properties. [21][22][23][24] Given these progresses, few studies explored the binding of the whole lanthanide series with DNA or correlated metal binding with enzyme activity. Such studies are important for revealing the coordination chemistry of lanthanides, and for DNA bioinorganic chemistry in general. 25,26 We recently performed an in vitro selection experiment using Ce 4+ as the intended metal cofactor. The selected DNAzyme (named Ce13d) was found to have similar activity with all trivalent lanthanides. 14 Therefore, Ce13d must bind all the lanthanides and this DNAzyme might provide a good scaffold for studying lanthanide binding. Herein, we employed Tb 3+ luminescence as a tool to study lanthanide binding to DNAzymes and its relation to catalytic activity. The secondary structure of the Ce13d DNAzyme complex is shown in Figure 1A. It consists of a substrate strand named Sub-rA with a single RNA linkage (rA, ribo-adenosine), and an enzyme strand named Ce13d. In the presence of a trivalent lanthanide, the substrate is cleaved into two fragments at the position pointed by the arrowhead. Lanthanides alone can catalyze the reaction and no div...

Abstract.Many homogeneous assays are complicated by the adsorption of probe molecules by the surface of reaction vessels, which are often made of polypropylene or polystyrene-based plastics. To solve this problem, many protein and surfactant-based blocking agents are used. However, these blockers may interfere with intended assays by sequestering transition metal ions, inducing protein denaturing, generating air bubbles or making pores in membranes. Coating surfaces with polyethylene glycol (PEG) through covalent linkages have been proven to be an effective method to minimize protein adsorption.However, this method is more difficult to apply on plastic surfaces and is quite expensive. While unmodified PEG is often considered as a non-adsorbing polymer, in this Technical Note, we report that PEG at very low ppm can still effectively block plastic surfaces. This method works for DNA, protein and liposome-based assays as long as the molecular weight of PEG is larger than 2000. PEG works due to multivalent hydrophobic interaction from its repeating methylene units. This Technical Note will not only facilitate biosensor development, but also enhance our understanding of the interaction between various molecules and plastic surfaces.3

Metallo-β-lactamases (MBLs) degrade a broad spectrum of antibiotics including the latest carbapenems. So far, limited success has been achieved in developing its inhibitors using small organic molecules. VIM-2 is one of the most studied and important MBLs. In this work, we screened 10 nanomaterials, covering a diverse range of surface properties including charge, hydrophobicity, and specific chemical bonding. Among these, graphene oxide and carbon nanotubes are the most potent inhibitors, while most other materials do not show much inhibition effect. The inhibition is noncompetitive and is attributed to the hydrophobic interaction with the enzyme. Adsorption of VIM-2 was further probed using protein displacement assays where it cannot displace or be displaced by bovine serum albumin (BSA). This information is useful for rational design inhibitors for MBLs and more specific inhibition might be achieved by further surface modifications on these nanocarbons.