<![CDATA[Silver nanoparticles (AgNPs) have attracted considerable interest due to their antibacterial properties and potential for metal-ion sensing. This study aimed to develop sodium alginate/silver nanoparticle (SA/AgNPs) beads using Asplenium nidus leaf extract and evaluate their antibacterial activity and colourimetric response toward Hg2+ ions. AgNPs were biosynthesised using Asplenium nidus leaf extract and incorporated into a sodium alginate matrix to form SA/AgNPs nanocomposite beads. The formation of AgNPs was indicated by a colour change from clear yellow to brown and confirmed by UV–Vis absorption in the range of 420–450 nm. The resulting SA/AgNPs nanocomposite beads exhibited antibacterial activity against Escherichia coli, producing an inhibition zone of approximately 1 mm, whereas sodium alginate beads without AgNPs showed no inhibition zone. In addition, the SA/AgNPs nanocomposite beads exhibited a concentration-dependent visual response toward Hg2+ ions (10–80 ppm), with a distinct colour change from brown to white, while the beads exposed to demineralised water remained brown after 24 h. These findings demonstrate that Asplenium nidus leaf extract can facilitate the biosynthesis of AgNPs and that the resulting SA/AgNPs nanocomposite beads exhibit both antibacterial activity and a visible response toward Hg2+ ions. The combination of a plant-mediated synthesis approach and alginate-based bead fabrication provides a simple platform with potential for antibacterial applications and preliminary colourimetric detection of Hg2+ ions.]]>
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