▎ 摘　　要

NOVELTY - A nano-biocomposite sensor comprises graphene oxide-chitosan (GO-CS) composite surface, where the composite surface is functionalized with silver nanoparticles. USE - Nano-biocomposite sensor for detecting heavy metal ion from contaminated water, where heavy metal ion is lead, cadmium, chromium, cobalt, mercury, lithium, or nickel (all claimed). ADVANTAGE - The nano-biocomposite sensor has improved sensing properties, enlarged active surface area, high electroconductivity, good water permeability, excellent film-forming ability, high affinity, and improved catalytic activity, and is highly sensitive towards heavy metals, achieves superior response with detection limit of 0.15 ppb and linear detection range of 0.2-40 ppb, and is effective to quantify heavy metal ions in water with high sensitivity and selectivity, cost-effective, easy-to-handle, and portable for on-site measurements. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for: 1. A method for making nano-biocomposite sensor, which involves: (i) obtaining individual mixtures of graphene oxide and chitosan by dissolving 75 mg graphene oxide in 5 ml methanol and dissolving 20 mg chitosan in 2 ml organic solvent, where the organic solvent is a mixture of ethyl cellulose, 2-(2-butoxyethoxy)ethyl acetate, and terpineol; (ii) ultrasonicating mixtures separately for half an hour to obtain homogeneous suspension; (iii) mixing both solutions of graphene oxide and chitosan followed by ultrasonication for 15 minutes to obtain uniform paste; (iv) depositing obtained paste on indium-tin oxide-coated glass substrate/slides by drop-casting to obtain GO-CS film; (v) dipping prepared film in 20 mM stalk solution of silver nitrate for half an hour to obtain functionalized GO-CS-silver film and washing with distilled water to remove unabsorbed silver; and (vi) drying functionalized film under an infrared lamp, and storing under dust-free conditions; and 2. A method of detecting heavy metal ion from contaminated water, which involves contacting the contaminated water with nano-biocomposite sensor.