Blocking Agent Optimization for Nonspecific Binding on Phage Based Magnetoelastic Biosensors

Magnetoelastic biosensors have been studied for the past few years for use in detecting bacteria for food safety. These magnetoelastic biosensors are composed of a bio-molecular recognition element and transducer platform (magnetoelastic resonator). Phages (bio-molecular recognition element) have been developed to provide very specific binding with Salmonella typhimurium bacteria. However, there is some binding (non-specific binding) of bacteria to the gold areas not covered with phage on both the measurement and control sensors. In those areas, a blocking agent is necessary to reduce the non-specific binding. The purpose of this study is to compare three of the often used blocking agents, BSA, milk and casein in different concentrations to determine the agent and the optimum concentration for blocking. To accomplish this, a set of measurement and control sensors were prepared using identical procedures except the control sensors were not immobilized with phage. The measurement and control sensors were then coated with a blocking agent of concentrations ranging from 0.1 to 5 mg/mL. SEM observations show that coating the magnetoelastic biosensors with BSA at a concentration of 1mg/mL yields the largest amount of specific binding of bacteria cells while also maintaining the largest ratio of specific to non-specific binding. This binding characteristic is a result of the physical and electrical structure of the blocking proteins. To verify that the blocking solutions made good contact with the sensor's surface, contact angle measurements were used to evaluate the wettability of the surface. Changes in the resonant frequency of the biosensors were found to agree with the results from SEM observations.