Colorimetric and electrochemical detection of pathogens in water using silver ions as a unique probe

Abstract

The manuscript highlights the efficacy of silver ions to act as a unique probe for the detection of bacterial contamination in water samples. The bacterial cell membrane adherence property of the silver ions was employed to develop two different bacterial detection assays employing colorimetric and electrochemical techniques. In one of the schemes, silver ion was used directly as a detector of bacteria in a colorimetric assay format, and in the other scheme surface-functionalized antibodies were used as a primary capture for specific detection of Salmonella enterica serovar Typhi. The colorimetric detection is based on silver-induced inhibition of urease activity and silver ion utilization by bacteria for the rapid screening of enteric pathogens in water. The specific detection of bacteria uses an antibody-based electrochemical method that employs silver as an electrochemical probe. The ability of silver to act as an electrochemical probe was investigated by employing Anodic Stripping Voltammetry (ASV) for targeted detection of Salmonella Typhi. for further insights into the developed assays, inductively coupled plasma mass spectrometry (ICP-MS) and transmission electron microscopy (TEM) studies were performed. The sensitivity of the developed assay was found to be 100 cfu mL −1 for colorimetric and 10 cfu mL −1 for electrochemical assay respectively.

Colorimetric Systems for the Detection of Bacterial Contamination: Strategy and Applications

“…Currently, the color development stage of colorimetric systems has five potential routes for signal visualization to determine the bacteria contamination level. The first route is based on external pH change-induced pH indicator reactions [ 19 , 20 , 21 , 22 , 23 ]. In this route, visual signal readouts can yield a color change in pH indicators via external pH changes.…”

“…Its hydrolytic activity also increases the ionic strength of the solution and, thus, can serve as a signal amplifier. Urease has been widely used in colorimetric bacterial detection based on its catalytic activity [ 19 , 20 , 21 ]. In this route, the type of pH indicator is also important, which determines the sensitivity of the system.…”

“…Signal readout can be obtained via the color change in a pH indicator by adding a catalytic compound that causes external pH change. Urease and a pH indicator have been widely used for the colorimetric detection of bacteria [ 19 , 20 , 21 ]. Urease is one of the most used catalytic compounds for the detection of bacterial contamination in food and the environment.…”

“…Considering the catalytic reaction of urease, the competitive binding ability of urease and bacterial cells to metal ions has been employed for the detection of bacteria [ 20 , 21 , 87 ]. It is well-known that urease can bind to other metals such as Ag + , Hg 2+ , Cu 2+ , and Zn 2+ , and metal-bound urease loses its hydrolyzing activity.…”

“…Ag ions also bind to urease, inhibiting urease activity by blocking its active site through sulfhydryl linkages that mediate a color change reaction in the pH indicator. Based on the binding ability of Ag ions to two substances, a colorimetric assay for the detection of Salmonella was developed ( Figure 1 B) [ 21 ]. In the absence of bacteria, Ag ions bind to urease, and the inhibited enzyme does not digest urea into ammonia, resulting in no pH change and no color change in the phenol red indicator.…”