Laser-Synthesized Plasmono-Fluorescent Si-Au and SiC-Au Nanocomposites for Colorimetric Sensing

Sensing represents one of the most rapidly developing areas of modern life sciences, spreading from the detection of pathogenic microorganisms in living systems, food, and beverages to hazardous substances in liquid and gaseous environments. However, the development of efficient and low-cost multimodal sensors with easy-to-read functionality is still very challenging. In this paper, stable aqueous colloidal suspensions (ζ-potential was between −30 and −40 mV) of ultrasmall (~7 nm) plasmonic Si-Au and SiC-Au nanocomposites were formed. Two variants of pulsed laser ablation in liquids (PLAL)—direct ablation and laser co-fragmentation—were used for this purpose. The co-fragmentation approach led to a considerable decrease in hydrodynamic diameter (~78 nm) and bandgap widening to approximately 1.6 eV. All plasmonic nanocomposites exhibited efficient multi-band blue emission peaking at ~430 nm upon Xe lamp excitation. Co-fragmentation route considerably (~1 order of magnitude) increased the PL efficiency of the nanocomposites in comparison with the laser-ablated ones, accompanied by a negligible amount of dangling bonds. These silicon-based nanostructures significantly affected the optical response of rhodamine 6G, depending on the synthesis route. In particular, directly ablated nanoparticles revealed a stronger influence on the optical response of dye molecules. The observed findings suggest using such types of semiconductor-plasmonic nanocomposites for multimodal plasmonic and colorimetric sensing integrated with luminescent detection capability.