ZnO nanorod matrix based electrochemical immunosensors for sensitivity enhanced detection of Legionella pneumophila

An ultrasensitive electrochemical immunosensor based on a ZnO nanorod (NR) matrix electrode was developed for detecting Legionella pneumophila for the first time. The ZnO NR matrix electrode was grown on an underlying Au working electrode (dia. 1.6 mm) using a hydrothermal method at a low temperature. A sandwich enzyme-linked immunosorbent assay was performed using the fabricated immunosensor. A primary antibody (1-4 μg/mL) was immobilized onto the ZnO NR matrix electrode by electrostatic interaction and the peptidoglycan-associated lipoprotein of L. pneumophila, as a component of Legionella antigen (1-5000 pg/mL) was bound to the primary antibody. A secondary antibody (1-4 μg/mL) conjugated to horseradish peroxidase was then bound to the antigen. The fabricated immunosensor was evaluated in a 0.1 M acetate buffer (pH 5) containing 0.05 mM 3,3′,5,5′-tetramethylbenzidine and 1 mM H ₂O₂ by cyclic voltammetry. In the fabricated immunosensors based on 1 μg/mL and 2 μg/mL antibody concentrations, the current output logarithmically increased with the L. pneumophila antigen concentrations from 1 to 5000 pg/mL. The detection limit is ∼1 pg/mL (S/N = 4) with excellent selectivity.