Polymer-nanoparticle composites find relevance in various fields ranging from optoelectronics to the biomedical sciences. Various efforts have been made to devise fabrication strategies that are simple, robust,and reproducible. Herein, we demonstrate a universal strategy to fabricate plasmon-active polymer-nanoparticle composites, exemplified by the incorporation of gold nanoparticles (AuNPs) into a triethylene glycol dimethacrylate (TEGDMA) polymer scaffold. The TEGDMA scaffold was synthesized on a planar glass support substrate via surface-initiated atomic transfer radical polymerization, followed by the immersion of the TEGDMA-coated glass substrate in a solution of AuNPs prepared via conventional wet-chemical synthesis. This led to the strong attachment of AuNPs to the TEGDMA nanolobes, which was confirmed by the UV absorption peak at 527 nm, due to localized surface plasmon resonance of AuNPs. More importantly, the nanolobe architecture facilitates nanoparticle trapping while allowing molecular access to the nanoparticle surface. This enabled us to further functionalize the incorporated AuNPs with thrombin binding aptamer and utilize the biofunctionalized polymer-nanoparticle composite as a thrombin sensor. The synergistic combination of metallic nanoparticles acting as a sensing module with a nonfouling polymer matrix acting both as a nonrigid scaffold and to screen biomolecules allowed the detection of thrombin with good sensitivity down to 0.01 ng/mL with a linear range over three orders of magnitude. Our work paves the way for the fabrication of reliable biomolecular sensors based on the polymer brush-nanoparticle architecture.