Evaluation of Antimicrobial, Antioxidant, and Cytotoxic Capabilities of Biosynthesized Silver Nanoparticles Assisted by the Hot Spring Originated Cyanobacterium <i>Desikacharya</i> sp. TPB‐4 Crude Extract and Its Fractionated Compound, Caffeic Acid

Cyanobacteria have evolved to produce polyphenolic compounds as adaptive strategies for surviving adverse environmental conditions, while these compounds exhibit diverse bioactivities, including antimicrobial, antioxidant, and anticancer properties, and facilitate the biogenic synthesis of nanoparticles. Despite these remarkable properties, the bioactive potential of hot spring-inhabiting cyanobacteria remains largely underexplored. To expand this information, silver nanoparticles (AgNPs) were fabricated using both the crude extract of the cyanobacterial strain Desikacharya sp. TPB-4 and its TLC-purified bioactive compound were identified as caffeic acid. Further UV-visible spectroscopy confirmed nanoparticle formation with characteristic surface plasmon resonance (SPR) peaks at 430 nm (CR-AgNPs) and 425 nm (CA-AgNPs). The more intense observed SPR peak for CA-AgNPs indicates their rapid synthesis because of the efficient reducing and stabilizing behavior of caffeic acid. Functional groups involved in capping and stabilization were identified by FTIR, while FE-SEM and TEM revealed spherical nanoparticles under 100 nm. XRD confirmed their face-centered cubic crystalline nature. Antioxidant assays showed enhanced radical scavenging, with CA-AgNPs exhibiting superior activity. Cytotoxicity studies using MIA PaCa-2 (cancerous) and MCF-10A (normal) cells revealed dose-dependent anticancer activity with reduced toxicity toward normal cells. This study highlights the significance of Desikacharya sp. TPB-4 and its nanoparticles in oxidative stress mitigation and therapeutic potential.