Drug-resistant bacterial infections are among the most severe physiological challenges facing human health. Therefore, the detection and inactivation of pathogenic bacteria remains a crucial therapeutic goal in modern society. In this study, we design multifunctional nanocomposites aimed at bacterial binding, fluorescence labeling, and synergistic antibacterial treatment. These nanocomposites are prepared by introducing cationic polymers with quaternary ammonium compounds onto silica nanoparticles using surface-initiated atom transfer radical polymerization, followed by incorporation of copper-doped carbon dots and modification of boronic acid. The cationic polymer units and boronic acid end groups enhance the bacterial binding capacity and synergistic bactericidal effects in cooperation with the carbon dots. Due to the stable fluorescent properties of carbon dots, the nanocomposites can generate fluorescence signals around bacteria, enabling bacterial fluorescence imaging. Overall, this study demonstrates a multifunctional nanocomposite-assisted strategy for bacterial labeling, imaging, and deactivation, providing a novel approach for bacterial detection and synergistic treatment.