Ag₂S-Film-Formation Mechanism in a Silver/Carbon Comb-Structured Biochemical Corrosion-Monitoring Sensor for Detecting H₂S Released from Escherichia coli

Herein, we report a biochemical corrosion-monitoring (BCM) sensor for detecting live E.coli . To analyze the current generation mechanism in the H 2 S response of the Ag/C sensor, we investigated the Ag 2 S film deposited on the Ag electrode surface after the H 2 S response. XPS surface analysis confirmed that the film deposited on the Ag electrode surface had a single composition of Ag 2 S. The Ag 2 S film thickness of 23 nm estimated by XPS depth analysis and the Ag 2 S deposition range of 0–12 μm estimated from cathodic reduction stripping experiments significantly agreed with the Ag 2 S film thickness and deposition calculated from the electrical quantity of the sensor. Therefore, it was concluded that all the reaction charges of the sulfurization reaction of the Ag/C sensor were converted into galvanic current ( I gal ), and the I gal generation of the Ag/C sensor in the E.coli solution was due to the sulfurization reaction of the Ag electrode. The Ag 2 S film can be removed by constant current electrolysis or by dissolution using a sulfuric acid solution containing thiourea. The I gal change in the E.coli solution of each sensor from which the Ag 2 S film was once removed was the same as that of an unused sensor.