Introduction: This study introduces a previously unreported sulfonated Naphthalimide derivative (NAP) designed as a multifunctional molecular scaffold for integrated fluorescence sensing and antimicrobial applications. Following functionalization with 3-(methylthio)propylamine, the compound was successfully immobilized onto silver nanoparticles (AgNPs) via thiomethyl anchoring, yielding a stable and highly functional nanohybrid system. The photophysical characteristics and selective metal ion sensing behavior of the resulting NAP-AgNPs were systematically evaluated. Importantly, this work constitutes the first example of sulfonate-bearing naphthalimide-functionalized AgNPs that simultaneously act as nanoparticle stabilizers, fluorescent sensing elements, and antimicrobial agents, thereby establishing a new multifunctional strategy for naphthalimide-silver nanomaterials. Methods: NAP was synthesized via the reaction of 4-sulfo-1,8-naphthalic anhydride with 3- (methylthio)propylamine and subsequently immobilized onto AgNPs through its thiomethyl groups. Structural and morphological characterizations were performed using NMR, FTIR, SEM, XRD, and DLS techniques. Photophysical properties were investigated by UV-Vis and fluorescence spectroscopy. Interaction studies with Cd2+, Mn2+, Cu2+, Co2+, Ni2+, Zn2+, Fe2+, Fe3+, Pb2+, Hg2+, and Ag+ ions were carried out. Antimicrobial activity was assessed against Gram- positive and Gram-negative bacteria. Results: NAP exhibited strong fluorescence emission at 520 nm, while NAP-AgNPs showed surface plasmon resonance with complete fluorescence quenching. Selective optical responses to Fe2+, Fe3+, Hg2+, and Ag+ were observed in both UV-Vis and fluorescence spectra, indicating promising sensing ability. Additionally, NAP-AgNPs displayed significant antimicrobial activity. Discussion: The study demonstrates that sulfonated NAP derivatives can serve as sensitive and selective probes for specific metal ions. The incorporation into AgNPs provided unique plasmonic properties, which may enhance sensing applications and enable dual-functional materials with antimicrobial capability. Conclusion: This work highlights the potential of NAP and NAP-AgNPs as photofunctional materials for selective metal ion sensing and as effective antimicrobial agents, suggesting future applications in environmental monitoring and biomedical fields.