Bio-inspired polydopamine layer as a versatile functionalisation protocol for silicon-based photonic biosensors.

Photonic biosensors have made major advances in recent years, achieving very high sensitivity, and progressing towards point-of-care deployment. By using photonic resonances, sensors can be label-free, which is particularly attractive for a low-cost technological realisation. A key remaining issue is the biological interface and the efficient and reliable immobilisation of binder molecules such as antibodies; many protocols are currently in use that have led to widely varying sensor performance.

Ion shuttling between emulsion droplets by crown ether modified gold nanoparticles.

Selective unidirectional transport of barium ions between droplets in a water-in-chloroform emulsion is demonstrated. Gold nanoparticles (GNPs) modified with a thiolated crown ether act as barium ion complexing shuttles that carry the ions from one population of droplets () to another (). This process is driven by a steep barium ion concentration gradient between and droplets.

Entropy-Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles.

It is shown that plasmonic gold nanoparticles functionalised with a thiolated 18-crown-6 ligand shell agglomerate spontaneously from aqueous dispersion at elevated temperatures. This process takes place over a narrow temperature range, is accompanied by a colour change from red to purple-blue and is fully reversible. Moreover, the temperature at which it occurs can be adjusted by the degree of complexation of the crown ether moiety with appropriate cations.

Ion Transport across Biological Membranes by Carborane-Capped Gold Nanoparticles.

Carborane-capped gold nanoparticles (Au/carborane NPs, 2-3 nm) can act as artificial ion transporters across biological membranes. The particles themselves are large hydrophobic anions that have the ability to disperse in aqueous media and to partition over both sides of a phospholipid bilayer membrane. Their presence therefore causes a membrane potential that is determined by the relative concentrations of particles on each side of the membrane according to the Nernst equation.

Design of artificial membrane transporters from gold nanoparticles with controllable hydrophobicity.

Gold nanoparticles with variable hydrophobicity have been prepared in three different size regimes following established methods. The control of hydrophobicity was achieved by complexation of the 18-crown-6-CH-thiolate ligand shell with potassium ions. Potassium dependent phase transfer of these particles from dispersion in water to chloroform was demonstrated, and the equilibrium partitioning of the particles in water-chloroform liquid/liquid systems was quantified by optical spectroscopy.

Monitoring pattern formation in drying and wetting dispersions of gold nanoparticles by ESEM.

We report an investigation of the self-assembly of patterns from functionalized gold nanoparticles (GNPs) by monitoring the process in situ by environmental scanning electron microscopy (ESEM) during both evaporation and condensation of the dispersant. As this method limits the choice of dispersants to water, GNPs functionalized with hydrophilic thiol ligands, containing poly(ethylene)glycol (PEG) groups, were used on a variety of substrates including pre-patterned ones. Particular emphasis was given to early stage deposition of GNPs, as well as redispersion and lift-off upon condensation of water droplets.