Synthesis and Applications of Plasmonic Hydrogels

The drop-wise addition of sodium alginate to a solution of calcium ions results in the formation of spherical Ca-alginate hydrogel beads. Gold nanoparticles (NPs) or nanoclusters (NCs) of varied size become incorporated into the hydrogel beads by adding them to the sodium alginate solution prior to synthesis. The extent of NP/NC loading depends on the concentration used in the sodium alginate solution while the size of the beads depends on the drop size and water content. The synthesis of hydrogel beads with gold NPs of varied size, shape, and aggregation state leads to plasmonic hydrogels with controlled optical properties due to their different wavelengths of the localized surface plasmon resonance (LSPR) peak of the NPs in the beads. The plasmonic properties can be further tuned by changing the composition of metal NPs within the hydrogel beads. The chemistry and properties are very different compared to the behavior of the NPs in water solutions without incorporation into the hydrogel. Functionalization and cross-linking the hydrogel by linkages other than Ca also affects the properties and provides advantages in terms of chemistry, stability, and applications. The hybrid hydrogel-metal NP plasmonic materials have applications in optical sensing, electrochemical analysis, photochemistry, and catalysis.