Development of a simple paper-based colorimetric diagnostic platform for sensitive detection of Salmonella typhimurium

Salmonella has long been recognised as the most common and primary cause of food poisoning in many countries. Its detection is still primarily based on conventional microbiological culture methods, which are considered as time-consuming and labour-intensive. Accordingly, the development of a rapid, simple, and reliable detection method to detect Salmonella is crucial to maintain public health safety and security. We report herein the development of a simple and rapid paper-based platform to detect S. typhimurium. Salmonella polyclonal antibody was utilised to capture the target cells, and a direct sandwich enzyme-linked immunosorbent assays (ELISA) format was then developed using an immunoglobulin G (IgG) conjugated with alkaline phosphatase (ALP) as the enzyme label. Nitro blue tetrazolium-(5-bromo-4-chloro-3-indolyl phosphate) was used as enzyme mediator system, which produced a bluish-purple colour on the surface of the paper platform. The developed colour signal was then analysed using a scanner for quantitative analysis. This method was highly sensitive with a limit of detection of 6 CFU mL^-1 without requiring expensive or advanced equipment. Bare eyes observation can be used for qualitative analysis, thus showing the ability of this method to be used for on-site detection and in resources-limited environment.