A study on a microfluidic platform for rapid food borne bacteria detection by consecutive magnetophoretic concentration and dielectrophoretic capturing

Abstract

Foodborne disease caused by consuming contaminated food is a major health concern worldwide. Foodborne disease has been a serious threat to public health. According to the world health organization, one in every six Americans suffers from foodborne disease in the United States, which is about 48 million annually. There are about 600 million people suffering from foodborne diseases, and 420,000 deaths worldwide. In the case of children who have a weak immune system, about one in three people die. For this reason, there is a growing demand for a system that can provide food safety information. In order to suppress and prevent foodborne disease, it is important to detect foodborne bacteria rapidly and accurately. In particular, food sample pretreatment is one of the most important processes for rapid detection of foodborne bacteria. In this study, a rapid bacteria detection system including food sample pretreatment is developed for on-site bacteria detection. In chapter 2, magnetophoresis based microfluidic device is proposed for rapid and efficient concentration of bacteria using a combination of a permanent magnet and commercial polyethylene tube. The channel length of the proposed device can be easily adjusted by simply adapting the different lengths of the tube and particles can be sufficiently concentrated even under high flow rate condition. In this study, bacteria (Bac) are conjugated with magnetic particles (MPs) and Staphylococcus aureus is utilized. The performance of the proposed device is evaluated by using two different types of food samples. Bacteria conjugated with magnetic particles (MPs-Bac) are spiked in milk sample and homogenized cabbage sample respectively. The concentration factor and the separation efficiency are higher than 100 times and 90%. In chapter 3, the dielectrophoresis based particle separation device is developed to separate MPs-Bac from MPs. In the concentrated sample, there are two different types of particles: 1) MPs-Bac, 2) MPs. Among them, MPs cause a signal error during bacteria detection. In order to improve the sensor accuracy, MPs-Bac are separated from the MPs by using positive dielectrophoretic force. The separation efficiency of the proposed separation device is evaluated using 1e1 CFU/ml - 1e4 CFU/ml and it is higher than 80% at all concentration conditions. In chapter 4, impedimetric based sensor is proposed for rapid detection of bacteria. The detection sensor is integrated with the bacteria concentration and separation device. After concentration, MPs-Bac flow to the sensor and are captured on the sensor electrode by positive dielectrophoretic force. Since bacteria admittance is higher than that of the solution, the current increases as bacteria are captured on the sensor. Therefore, bacteria in a food sample can be detected by measuring the current change. The proposed bacteria detection sensor is evaluated using 5 CFU/ml - 5e3 CFU/ml concentration samples and the signal is measured for 10 min. The signal variation is about 0.64 mV at 5 CFU/ml. In conclusion, the proposed microfluidic platform can rapidly and accurately detect the bacteria at low concentration (5 CFU/ml) sample within 45 min (homogenization of food sample (5 min) + Bac and MPs conjugation (30 min) + signal measurement (10 min)). It might be applicable for sample pretreatment or monitoring of bacteria level in various fields such as food, medicine, industry, and environment.