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

An immune-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 degreesC 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 x 10(4) and 2.2 x 10(6) colony forming units (CFU) ml(-1). The whole detection process could be completed within 2 h. (C) 2001 Elsevier Science B.V. All rights reserved.