Foodborne diseases are a growing public health problem. In recent years, many rapid detection methods have been reported, but most of them are still in lab research and not practical for use in the field. In this study, a portable and automatic biosensing instrument was designed and constructed for separation and detection of target pathogens in food samples using nanobead-based magnetic separation and quantum dots (QDs)-labeled fluorescence measurement. The instrument consisted of a laptop with LabVIEW software, a data acquisition card (DAQ), a fluorescent detector, micro-pumps, stepper motors, and 3D printed tube holders. First, a sample in a syringe was mixed with magnetic nanobead-antibody (MNB-Ab) conjugates and then injected to a low binding reaction tube. After incubation and magnetic separation, target bacterial cells were captured and collected and the solution was pumped out. Then the QD-antibody (QD-Ab) conjugates were pumped into the reaction tube to form the MNB-Ab-cell-Ab-QD complexes that were then collected by magnetic separation and resuspended in PBS buffer solution through air pressure control. Finally, the sample solution was pushed into the detection tube by an air pump and the fluorescence intensity was measured using a fluorescent detector. A virtual instrument (VI) was programmed using LabVIEW software to provide a platform for magnetic separation, fluorescent measurement, data processing, and control. The DAQ was used for data communication. The results showed that the separation efficiency of this instrument was 78.3 ± 3.4% and 60.7 ± 4.2% for E. coli O157:H7 in pure culture and ground beef samples, respectively. The limit of detection was 3.98 × 103 and 6.46 × 104 CFU/mL in pure culture and ground beef samples, respectively. Sample preparation and detection could be finished in 2 hours. The instrument was portable and automatic with great potential to serve as a more effective tool for in-field/on-line detection of foodborne pathogenic bacteria in food products
