Early 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 of Listeria monocytogenes combining 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 the Listeria cells 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 588 nm for bacteria quantification. This proposed biosensor was able to detect Listeria monocytogenes as low as 1.0 × 10² CFU/mL, and had the mean recovery of 95.1% for Listeria in 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.

食品中病原细菌的早期筛查在食源性疾病的预防和控制中起着重要的作用。在这项研究中，我们开发了一种光学生物传感器，可结合免疫磁分离，脲酶催化和pH指示快速灵敏地检测单核细胞增生李斯特菌。通过抗生蛋白链菌素-生物素结合与单克隆抗体（MAb）缀合的磁性纳米珠（MNB）用于特异性和有效地将利斯特氏菌细胞与背景分离，以形成磁性标记的细菌。然后，用尿素酶修饰的金纳米颗粒（AuNPs）和通过静电吸附的多克隆抗体（PAbs）与磁性标记细菌反应形成MNB-MAb-李斯特菌-PAb-AuNP-脲酶复合物。配合物中的尿素酶可以催化尿素水解成碳酸铵，这可能导致尿素溶液的pH值增加。将溴甲酚紫与酚红和溴百里酚蓝进行了比较，并被选为监测颜色变化的最佳pH指示剂，可以在588 nm的特征波长处进行测量以进行细菌定量。提出的这种生物传感器能够检测低至1.0×10 ²  CFU / mL的单核细胞增生李斯特菌，并且在生菜样品中李斯特菌的平均回收率为95.1％。这种光学生物传感器已经显示出其潜力，可以提供一种简单，低成本和灵敏的检测方法来预防和控制食源性疾病。