Rapid detection of Salmonella typhimurium using immunomagnetic separation and immuno-optical sensing method

An immuno-optical absorption method with immunomagnetic separation was developed for rapid detection of Salmonella typhimurium. The magnetic microbeads coated with anti-Salmonella were used to separate Salmonella from sample solutions by the specific antibody–antigen interaction at room temperature for 30 min. Then the “sandwich” complexes (anti-Salmonella coated on to magnetic microbeads, Salmonella, anti-Salmonella labeled with alkaline phosphatase) were formed by binding the microbeads, which captured Salmonella from sample solution, with alkaline phosphatase-labeled anti-Salmonella at room temperature for 30 min. The “sandwich” complexes were separated from the solution by a magnetic field and incubated in p-nitrophenyl phosphate substrate at 37°C for 30 min to produce p-nitrophenol by the enzymatic hydrolysis. The cell number of Salmonella was detected by measuring absorbance of p-nitrophenol at 404 nm. A linear response was found between 2.2×104 and 2.2×106 colony forming units (CFU) ml−1. The whole detection process could be completed within 2 h.