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

Titanium dioxide (TiO2) or titania shows great promise in detoxification and drug delivery. To reach its full potential, it is important to interface TiO2 with biomolecules to harness their molecular recognition function. To this end, DNA attachment is an important topic. Previous work has mainly focused on long double-stranded DNA or single nucleotides. For biosensor development and targeted drug delivery, it is more important to use single-stranded oligonucleotides. Herein, the interaction between fluorescently labeled oligonucleotides and TiO2 nanoparticles is reported. The point of zero charge (PZC) of TiO2 is around 6 in water or in acetate buffer, so they are positively charged at lower pH.However, if in phosphate or citrate buffer, the particles are negatively charged even at pH ~2, suggesting strong adsorption of buffer anions. DNA adsorption takes places mainly via the phosphate backbone although the bases might also have moderate contributions. Peptide nucleic acids (PNA) with an amide backbone cannot be adsorbed. DNA adsorption is strongly affected by inorganic anions, where phosphate and citrate can strongly inhibit DNA adsorption. DNA adsorption is also promoted by adding salt or lowering pH. DNA adsorption is accompanied with fluorescence quenching and doublestranded DNA showed reduced quenching, allowing detection of DNA using TiO2 nanoparticles.3

ABSTRACT:The property of DNA is strongly influenced by counter ions. Packing a dense layer of DNA onto a gold nanoparticle (AuNP) surface generates a diverse range of novel physical properties such as a sharp melting transition, protection of the DNA against nuclease and enhanced penetration of biological membranes. In this work, we show that the density of the DNA on AuNPs is a function of counter ion size, where smaller Li + allows ~30% more DNA packing compared to the larger Cs + . At the same time, the initial DNA adsorption kinetics are slower with Li + compared to that with Cs + , which is attributed to the easier dehydration of Cs + . This is also supported by Cs + being much more effective in aggregating citrate-capped AuNPs than Li + . This work suggests that detailed physicochemical information at the bio/nano interface can be obtained by using counter ions as probes.

No abstract

Graphene oxide adsorbs single-strand fluorescent probe DNA, and the adsorbed probe can be desorbed by adding the complementary target DNA. Using this method, many biosensor studies have been carried out. We recently proposed a two-step mechanism for this sensing reaction: non-specific probe displacement followed by hybridization in the solution. Only about one out of six added target DNA is hybridized with the adsorbed probe to generate signal, leading to relatively low sensitivity. In this work, we aim to test whether surface blocking agents can minimize non-specific target adsorption and increase hybridization efficiency. Over ten blocking agents (polymers, surfactants, and DNA) were screened based on their effect on probe DNA adsorption and target DNA induced probe desorption. DNA oligonucleotides show significant and controllable enhancement in sensor sensitivity. The effect of DNA length and sequence was systematically investigated. Under optimized conditions, the sensor sensitivity was enhanced by nearly 10-fold. Using the same blocking method, sensitivity enhancement of other targets was also achieved, including adenosine and Hg(2+) with DNA aptamer probes. This reported surface blocking strategy can generally improve graphene oxide and potentially other surface adsorption based biosensors for metal ions, small molecules, and DNA.