Gold nanoparticle assemblies through hydrogen-bonded supramolecular mediators

Cationic recognition by tert-butylcalix[4]arene-functionalized nanoprobes

A nanoparticle-based strategy has been demonstrated using structurally-tailored tert-butylcalixarenes immobilized on gold nanoparticles to tune the guest access to the calixarene cone cavity for cationic recognition. This strategy exploits the interparticle charge-induced aggregation upon selective capture of metal cations into the nanoparticle-immobilized tert-butylcalixarenes, which produces calorimetric changes for the detection. A possible pathway for the binding of M(n+) into the t-BCA structure and the interparticle interaction is proposed for the formation of an electric double layer inducing the interparticle association responsible for the red-shifted surface plasmon resonance band of the nanoparticles. The value of this class of calorimetric nanoprobes will be in the area of designing advanced host-guest probes using a variety of calixarene ligands for ionic recognition in a simplistic detection format.

Thin film assemblies of molecularly-linked metal nanoparticles and multifunctional properties

The use of metal nanoparticles as building blocks toward thin film assembly creates intriguing opportunities for exploring multifunctional properties. Such an exploration requires the ability to engineer the size, shape, composition, and especially interparticle properties in nanoparticle assemblies for harnessing the collective properties of the nanoscale building blocks. This article highlights some of the important findings of our investigations of thin film assemblies of molecularly linked nanoparticles for exploiting their multifunctional and collective properties in molecular recognition and chemical sensing. The thermally activated processing approach presents a viable pathway for nanoengineering metal, alloy, and core-shell nanoparticles as building blocks. The molecular mediator-templating approach offers an effective strategy to thin film assemblies of the nanoscale building blocks that impart multifunctional properties. In such thin film assemblies, the interparticle interactions and structures dictate the correlation between the nanostructural parameters and the optical and electrical properties. By highlighting selected examples involving ligand-framework binding of ionic species at the film/liquid interface and electrical responses to molecular sorption at the film/gas interface, the multifunctional properties of the thin film assemblies are further discussed in terms of interparticle covalent, hydrogen bonding, ionic, or van der Waals interactions in a framework-type architecture for the creation of molecular recognition and chemical sensing sites that can be tuned chemically or electrochemically. Implications of these insights to expanding the exploration of nanoparticle thin film assemblies for a wide range of technological applications are also discussed.