This article presents the synthesis and physicochemical behavior of dual-responsive plasmonic nanoparticles with reversible optical properties based on protein-coated gold nanoparticles grafted with thermosensitive polymer brushes by means of surface-initiated atom transfer radical polymerization (SI-ATRP) that exhibit pH-dependent thermo-responsive behavior. Spherical gold NPs of two different sizes (15 nm and 60 nm) and with different stabilizing agents (citrate and cetyltrimethylammonium bromide (CTAB), respectively) were first capped with bovine serum albumin (BSA). The resulting BSA-capped NPs (Au@BSA NPs) exhibited not only extremely high colloidal stability under physiological conditions, but also a reversible U-shaped pH-responsive behavior, similar to pure BSA. The ϵ-amine of the L-lysine in the protein coating was then used to covalently bind an ATRP-initiator, allowing for the SI-ATRP of thermosensitive polymer brushes of oligo(ethylene glycol) methacrylates with an LCST of 42 °C in pure water and around 37 °C under physiological conditions. Such protein coated nanoparticles grafted with thermosensitive polymers exhibit a smart pH-dependent thermosensitive behavior.