Reversible Ligation of Programmed DNA-Gold Nanoparticle Assemblies.

We demonstrate a new method to reversibly cross-link DNA-nanoparticle dimers, trimers, and tetramers using light as an external stimulus. A DNA interstrand photo-cross-linking reaction is possible via ligation of a cyano-vinyl carbazole nucleoside with an opposite thymine when irradiated at 365 nm. This reaction results in nanoparticle assemblies that are not susceptible to DNA dehybridization conditions. The chemical bond between the two complementary DNA strands can be reversibly broken upon light irradiation at 312 nm. This is the first example of reversible ligation in DNA-nanoparticle assemblies using light and enables new developments in the field of programmed nanoparticle organization.

Cells on hierarchically-structured platforms hosting functionalized nanoparticles.

In this work, we report on a novel approach to develop hierarchically-structured cell culture platforms incorporating functionalized gold nanoparticles (AuNPs). In particular, the hierarchical substrates comprise primary pseudo-periodic arrays of silicon microcones combined with a secondary nanoscale pattern of homogeneously deposited AuNPs terminated with bio-functional moieties. AuNPs with various functionalities (i.e. oligopeptides, small molecules and oligomers) were successfully attached onto the microstructures. Experiments with PC12 cells on hierarchical substrates incorporating AuNPs carrying the RGD peptide showed an impressive growth and NGF-induced differentiation of the PC12 cells, compared to that on the NP-free, bare, micropatterned substrates. The exploitation of the developed methodology for the binding of AuNPs as carriers of specific bio-functional moieties onto micropatterned culture substrates for cell biology studies is envisaged.

Encapsulated enzymes with integrated fluorescence-control of enzymatic activity.

A fluorescence-based particle sensor for oxaloacetic acid is presented. In the presence of nicotinamide adenine dinucleotide as a cofactor, oxaloacetic acid is converted by malate dehydrogenase into l-malic acid. The progress of the reaction is monitored by sensing of proton consumption with an integrated pH sensor. The kinetics of this sensor are investigated on a single particle level. This work demonstrates the feasibility to detect analytes upon their enzymatic conversion into a product, which in turn can be sensed with a fluorophore responding to changes in the concentration of this product. Integration of enzymes and fluorophores into one carrier particle, as demonstrated here for the case of polyelectrolyte polymer capsules, allows the range of analytes that can be detected with fluorescence to be extended, as it enhances selectivity. This coupled system allows enzymatic activity, as well as the kinetics of malate dehydrogenase, to be monitored.

Gold nanoparticles and fluorescently-labelled DNA as a platform for biological sensing.

In the past decade gold nanoparticle-nucleic acid conjugates became progressively important for biomedical applications. Fluorophores attached to nucleic acid-gold nanoparticle conjugates have opened up a new era of biological sensing. The most promising advancement in this field was the invention of the so-called 'nano-flare' systems. These systems are capable of detecting specific endocellular targets such as mRNAs, microRNAs or small molecules in real time. In this minireview, we discuss the current progress in the field of DNA-nanoparticles as sensors, their properties, stability, cellular uptake and cytotoxicity.