Phycocyanin, a blue fluorescent pigment-protein complex derived from blue-green algae (Spirulina platensis), exhibits excellent bio reductant and stabilizing properties. In this study, an eco-friendly and cost-effective approach was developed to synthesize silver nanoparticles (AgNPs) using purified phycocyanin extract. The formation of nanoparticles was indicated by a color change from blue to brown and confirmed through UV–Visible spectroscopic analysis, showing a characteristic peak around 420 nm. The biosynthesized AgNPs demonstrated bright red fluorescence under UV light, enabling their use as a natural fluorescent bio-ink for anti-counterfeiting applications. The method avoids chemical reducing agents, promotes sustainability, and opens a new dimension for phycocyanin-based nanomaterials in security printing and bio-imaging.