Self-assembled monolayer (SAM) modification is a widely used method to improve the functionality and stability of bulk and nanoscale materials. For instance, the chemical compatibility and utility of solution-phase nanoparticles are often improved using covalently bound SAMs. Herein, solution-phase gold nanoparticles are modified with thioctic acid SAMs in the presence and absence of salt. Molecular packing density on the nanoparticle surfaces is estimated using X-ray photoelectron spectroscopy and increases by ~20% when molecular self-assembly occurs in the presence vs. the absence of salt. We hypothesize that as the ionic strength of the solution increases, pinhole and collapsed-site defects in the SAM are more easily accessible as the electrostatic interaction energy between adjacent molecules decreases thereby facilitating the subsequent assembly of additional thioctic acid molecules. Significantly, increased SAM packing densities increase the stability of functionalized gold nanoparticles by a factor of two relative to nanoparticles functionalized in the absence of salt. These results are expected to improve the reproducible functionalization of solution-phase nanomaterials for various applications.

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Increasing the citrate concentration during the seeded growth synthesis of gold nanoparticles yields materials with decreased aspect ratios and increased defect densities. The stability of these nanoparticles is attributed to variations in their overall Gibb's free energy.

Biosensors possess recognition elements that bind to target molecules which lead to detectable signals. Incorporation of noble metal nanomaterials into biosensors allows for rapid and simple biomolecule detection. Herein, recent developments in affinity nanosensors will be discussed. These sensors often include naturally occurring recognition elements such as antibodies and DNA. As samples become more complex, new recognition elements are sought. For instance, plastic antibodies provide alternative and more environmentally stable recognition elements than traditional antibodies. Molecular imprinted polymers, a class of plastic antibodies, promote biomolecule recognition and detection. The incorporation of noble metal nanomaterials into molecular imprinted polymer biosensors for real world applications will be explored. Further improvements in the design of artificial recognition agents are envisioned to facilitate new methods for complex biological and chemical analyses.

Local refractive index sensitivity modelling using the plasmonic properties of gold nanospheres assists in the elucidation of the nanoparticle-rattle formation as a function of sample age and storage conditions.