Electrochemical Magnetic Bead-Based Immunosensor for Rapid and Quantitative Detection of Probiotic Lactobacillus rhamnosus in Dairy Products

Rapid and quantitative detection of probiotic Lactobacillus rhamnosus at the strain level is important for quality control of probiotic products. In this study, an electrochemical magnetic bead-based immunosensor (EMBI) was developed for the specific quantification of probiotic L. rhamnosus strain GG (LGG) in dairy products. Magnetic beads coupled with a specific antibody against the pilus subunit SpaA of LGG (Ab-SpaA) were prepared to selectively capture LGG from the background, which were then detected using horseradish peroxidase-labeled Ab-SpaA. The resultant sandwich-type immunocomplexes were separated by magnetic force and detected by measuring current signals using a magnetic glassy carbon electrode (MGCE) and the hydroquinone (HQ)/H2O2 system. Under optimal experimental conditions, the developed EMBI showed a linear relationship between the peak current and the logarithmic value of LGG concentration ranging from 2.56 × 103 to 2.56 × 107 CFU mL−1 with a detection limit of 22 CFU mL−1. EMBI detection is LGG specific, and no cross-reaction was observed for tested strains of other lactic acid bacterial species. The EMBI was successfully applied for LGG determination in commercial milk, yogurt, milk beverage products, and spiked dairy samples, with a recovery rate in the range of 91.74–108.67%. The entire detection process could be completed within 3 h. The proposed biosensor shows low-cost, rapid response, and high sensitivity and specificity and could be a promising technique for quality detection and functional evaluation of probiotic products containing LGG.