An optical biosensor using immunomagnetic separation, urease catalysis and pH indication for rapid and sensitive detection of Listeria monocytogenes

摘要

Highlights•The detection limit of this biosensor was 102CFU/ml forListeria monocytogenes.•The pH indication with bromcresol purple was used to determine the amount ofListeria.•Urease catalysis was used to amplify the detection signal.•The mean recovery ofListeriain the spiked lettuce samples was 98.2%.AbstractEarly screening of pathogenic bacteria in foods plays an important role in foodborne disease prevention and control. In this study, we developed an optical biosensor for rapid and sensitive detection ofListeria monocytogenescombining immunomagnetic separation, urease catalysis and pH indication. The magnetic nanobeads (MNBs) conjugated with monoclonal antibodies (MAbs) by streptavidin-biotin binding were used for specifically and efficiently separating theListeriacells from background to form magnetically labeled bacteria. Then, the gold nanoparticles (AuNPs) modified with urease and polyclonal antibodies (PAbs) by electrostatic adsorption were used to react with the magnetically labeled bacteria to form the MNB-MAb-Listeria-PAb-AuNP-urease complexes. The urease in the complexes could catalyze the hydrolysis of the urea into ammonium carbonate, which could lead to an increase in the pH value of the urea solution. Bromcresol purple was compared with phenol red and bromothymol blue and selected as the best pH indicator to monitor the color change, which could be measured at the characteristic wavelength of 588nm for bacteria quantification. This proposed biosensor was able to detectListeria monocytogenesas low as 1.0×102CFU/mL, and had the mean recovery of 95.1% forListeriain the spiked lettuce samples. This optical biosensor has showed its potential to provide a simple, low-cost and sensitive detection method for prevention and control of foodborne diseases.