Abstract:
Optical and electrochemical sensor for H2S sensing were developed using silver nanoparticles (AgNPs) immobilized onto polyelectrolyte membranes (PEMs) as substrate. Two approach for the deposition of the silver nanoparticles namely in-situ and ex-situ were compared for their sensing efficiency. The Poly(diallyldimethylchloride) (PDADMAC) and Poly(sodium styrenesulfonate) (PSS) were used to build PEMs via layer-by-layer assembly mechanism as polycation and polyanion respectively. In situ synthesis of silver nanoparticles was achieved by dipping the PEM coated substrate in silver nitrate (AgNO₃) solution followed by sodium borohydride (NaBH₄) as reducing agent. For ex situ technique, a monolayer of pre-synthesized silver nanoparticles was deposited as single top layer on the PEMs. The silver nanoparticles were synthesized by capping with a copolymer of styrene sulfonate and maleic acid at various concentrations. The successful synthesis of silver nanoparticles was confirmed using UV-Vis spectroscopy by monitoring the plasmon band peak at 400 nm which is characteristic of AgNPs. Screen printed electrodes were used for electrochemical sensing and were modified with the PEM following 2 different approach that were single electrode coating and double electrodes coating. The equivalent circuit was used to study the Nyquist plot of impedance results. Both types of composite membranes were exposed to hydrogen sulfide (H₂S) as analyte and compared by UV-Vis spectroscopy for optical sensing and LCR meter for impedance sensing. Ex situ synthesis technique had significant result for optical sensing, but in situ synthesis technique had better sensitivity for impedance sensing.
