Anisotropic gold nanoparticles often exhibit superior optical properties compared to spherical ones, in part due to intense electric field localization near sharp geometric features and a broadly tunable localized surface plasmon resonance. As a result, anisotropic nanoparticles are attractive building blocks for surface-enhanced Raman spectroscopy (SERS) substrates. To unlock the full potential of such substrates, one should be able to (1) generate a sufficient number of SERS hotspots with structures of controlled shape and size and (2) remove ligands so that analytes can easily access nanoparticle surface sites. Here, we develop a synthetic strategy for the shape- and size-controlled anisotropic growth of gold nanoparticles (concave rhombic dodecahedra and concave cubes, 70–135 nm characteristic length) from spherical seeds anchored on a structurally complex surface (common filter paper) and subsequently combine electrodynamics and electronic structure calculations with experiment to systematically characterize these substrates using SERS. Furthermore, we explore the generalizable functionality of these substrate-stabilized nanoparticles by using a continuous extraction method to partially remove surface ligands that were necessary for anisotropic growth, enabling the specific SERS detection of serotonin, a molecular neurotransmitter with a weak affinity for gold.

Thiol-Michael "click" reactions are essential synthetic tools in the preparation of various materials including polymers, dendrimers, and other macromolecules. Despite increasing efforts to apply thiol-Michael chemistry in a controlled fashion, the selectivity of base- or nucleophile-promoted thiol-Michael reactions in complex mixtures of multiple thiols and/or acceptors remains largely unknown. Herein, we report a thorough fundamental study of the selectivity of thiol-Michael reactions through a series of 270 ternary reactions using H NMR spectroscopy to quantify product selectivity. The varying influences of different catalysts/initiators are explored using ternary reactions between two Michael acceptors and a single thiol or between a single Michael acceptor and two thiols using three different catalysts/initiators (triethylamine, DBU, and dimethylphenylphosphine) in chloroform. The results from the ternary reactions provide a platform from which sequential quaternary, one-pot quaternary, and sequential senary thiol-Michael reactions were designed and their selectivities quantified. These results provide insights into the design of selective thiol-Michael reactions that can be used for the synthesis and functionalization of multicomponent polymers and further informs how catalyst/initiator choice influences the reactivity between a given thiol and Michael acceptor.

Bimetallic nanoparticles formed of poorly miscible alloys are attractive for applications in surface-enhanced Raman scattering (SERS), as they could allow the detection and study of analytes that do not bind well to typical plasmonic substrates, particularly important biomolecules such as serotonin. Despite their potential importance for SERS applications, the plasmonic and geometric properties of these alloys are not well characterized. Here, we present a method for calculating the thermodynamically minimized geometries of these nanoparticles as a function of their surface, bulk, and metallic phase interface energies. We show how the geometry varies as a function of composition, from core–shell, to Janus, to phase-separated, and discuss the importance of accurately modeling the metallic phase interface region to capture particle geometries. Finally, we use the calculated Janus geometries for the AuNi and AgNi systems to explore the suitability of these particles for use in SERS and identify the ideal compositions to maximize local field enhancement on the Ni-rich phase of the particle using the finite-difference time-domain method.

Thiol-Michael reactions have become the subject of increased interest due to their "click" nature, meaning they are broadly applicable, rapid, tolerant of many different reaction conditions, and high yielding. These reactions have proven to be useful in organic materials synthesis. To gain more knowledge of specific thiol-Michael reactions which yield highly selective products in a short amount of time, an investigation of ternary reactions between a single Michael acceptor and two thiols was conducted. All possible ternary combinations of six Michael acceptors and five thiols were attempted using three initiators in two solvents. The relative ratios of each product were compared using 1 H NMR spectroscopy. Results indicated a similar number of highly selective ternary combinations in both solvents. Analysis of the results of these combinations resulted in the development and optimization of quaternary reactions, involving two thiols and two Michael-acceptors, to yield only two selective products. A combination of these ternary and quaternary results might allow for the creation of large multi-functionalized pendant polymers, dendrimers, and other macromolecules with fewer intermediate steps and minimal purification. v