In this study, the optical properties of systems composed of biotin-functionalized gold nanoislands on the surface of silica xerogel monoliths (SiO2) were investigated, aiming to develop an inorganic and inert solid platform for biosensors based on Localized Surface Plasmon Resonance (LSPR) due to their high sensitivity to changes in the nearby chemical environment. The silica xerogels were synthesized through a two-step catalytic sol-gel process, where a solution of deionized water, ethanol, and tetraethyl orthosilicate was mixed under cold magnetic stirring, with a molar ratio of 8.5:3.5:1, and solutions of hydrochloric acid and ammonium hydroxide were used as catalysts for hydrolysis and condensation, respectively, in polypropylene molds. Later, the gels were aged in molds and converted to xerogels by drying at 600 C degrees in an oven. To create the gold nanoislands, a thin film of 20 nm Au was deposited on one of the top surfaces of the xerogels by sputtering, and then the Au@SiO2 xerogels were subjected to heat treatment in an electric furnace. A color change of the samples from blue to pink was observed, characteristic of gold nanoparticles. Then, the AuNP@SiO2 xerogel systems were functionalized in two consecutive steps with cysteamine (CA) and N-hydroxysuccinimide-biotin (NHSB) for the detection of avidin in an aqueous solution. The biotin-avidin pair is a well-known system for testing biosensors, due to its high specificity and very low sensitivity. The functionalization process was monitored by UV-Vis optical absorbance for each step. Aqueous solutions with concentrations of avidin (10(-6) M, 10(-7) M, 10(-8) M, 10(-9) M and 10(-10) M) were used to test detection and sensitivity. An average shift of 52 nm was observed in the absorbance spectrum of all tested concentrations, indicating that this system is a promising structure for plasmonic biosensor applications.