Longevity analysis of biosensor for Salmonella typhimurium detection in food

Abstract: A biosensor essentially consists of two main components, a physical transducer and a biorecognition element. In this study, antibody-based magnetoelastic (ME) biosensor specific to Salmonella typhimurium has been developed by immobilizing biorecognition element onto the physical transducer. Rabbit polyclonal antibody, which was an immune system-related protein called immunoglobulins, was used as the biorecognition. A magnetostrictive platform was served as the transducer, since it offered wireless or remote detecting, which was a unique advantage over conventional sensor platforms. Amorphous magnetostrictive alloy was used as the sensor platform, which was mechanically polished using fine grit paper to reduce the thickness to 15 μm to decrease the initial mass, and magnetostrictive strips were made with the size of 5 mm×1 mm using an auto controlled, microdicing saw. Then the diced sensors were ultrasonically cleaned in methanol solution to remove grease and debris left by the dicing process. And antibody was immobilized on the magnetostrictive platform using Langmuir-Blodgett (LB) technique, in which seven monolayers containing antibody were transferred onto the magnetostrictive sensor surface using a LB film balance KSV 2200 LB. After antibody immobilization, the biosensors were divided into 3 sets and maintained in 3 constant temperature humidity chambers with temperature of 25, 45 and 65℃, respectively. Before testing, the biosensors were allowed to attain room temperature and then immersed in S. typhimurium solution with the concentration of 1×109 cfu/mL for 30 minutes to bind bacterial cells. Due to the magnetoelastic nature of the amorphous magnetostrictive alloy, the sensor exhibited a physical resonance when it underwent a time-varying magnetic field, and a shift in resonance frequency of the magnetostrictive sensor depended only on the mass change when testing environmental parameters were invariable. In this study, the environment was kept constant, and the changes in the resonance frequency of biosensors attributting to the binding of Salmonella typhimurium were recorded by HP network analyzer 8751A over the testing period, and the binding was also confirmed by scanning electron microscopy (SEM) micrographs. According to the shift in resonance frequency due to the binding of Salmonella typhimurium, the binding density bound on the biosensor was calculated. In order to confirm the binding, different regions of each sensor surface were examined and photographed using SEM, the number of cells bound to the sensor surface was directly counted from SEM images and statistically converted to an area density of bacteria attached to the sensor surface, and then compared with that calculated from the shift in resonance frequency. The longevity of the sensors at different temperatures was investigated according to the binding density of Salmonella typhimurium. Meanwhile, the activation energy was calculated using Arrhenius Equation. The results showed that at each temperature, the binding ability of antibody to S. typhimurium decreased gradually over the testing period, and the higher the temperature, the lower the longevity of the biosensor. The longevity of polyclonal antibody-based magnetostrictive sensor was about 30, 8 and 5 days at 25℃ (room temperature), 45 and 65℃, respectively. And its activation energy calculated by Arrhenius Equation was about 13.024 kJ/mol.