Prediction of the Mass Sensitivity of Phage-Coated Magnetoelastic Biosensors for the Detection of Single Pathogenic Bact
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Prediction of the Mass Sensitivity of Phage-Coated Magnetoelastic Biosensors for the Detection of Single Pathogenic Bacteria Shin Horikawa1, Suiqiong Li1, Yating Chai1, Valerly A. Petrenko2, and Bryan A. Chin1 1 Materials Research and Education Center, Auburn University, AL 36849, U.S.A. 2 Department of Pathobiology, Auburn University, AL 36849, U.S.A.
ABSTRACT Freestanding, strip-shaped magnetoelastic (ME) biosensors are a class of wireless, massbased biosensors that are being developed for the real-time detection of pathogenic bacteria for food safety and bio-security. The mass sensitivity of these biosensors operating in longitudinalvibration modes is known to be largely dependent on the position of masses attached to the sensor surfaces. Hence, considering this dependence is crucial to the detection of lowconcentration target pathogens, including single pathogenic bacteria, because their local attachment may cause varying sensor responses. In a worst case scenario, the resultant sensor responses (i.e., mass-induced resonance frequency changes of the sensor) may be too small to be detected despite the attachment of the target pathogenic masses. To address the issue, phagecoated ME biosensors (magnetostrictive strips (4 mm × 0.8 mm × 30 ȝm) coated with a phage probe specifically binding streptavidin protein) with localized masses (streptavidin-coated polystyrene beads) were fabricated, and mass-position-dependence of the sensor’s sensitivity under the fundamental-mode vibration was experimentally measured. In addition, threedimensional finite element (FE) modal analysis was performed using the CalculiX software to simulate the phenomena. The experimental and theoretical results show close agreement: (1) the mass sensitivity was low when the mass was positioned in the middle of the sensor’s longest dimension and (2) a much higher mass sensitivity was, by contrast, obtained for the equivalent masses placed at both ends of the strip-shaped sensor. Furthermore, FE models were constructed for differently sized, phage-coated ME biosensors (100 – 500 ȝm in length with different widths and thicknesses) loaded with a single bacterial mass (2 ȝm × 0.4 ȝm × 0.4 ȝm, 1.05 g/cm3) at varying longitudinal positions. The mass sensitivity was found to be approximated by a massposition-dependent Boltzmann function whose amplitude is inversely proportional to the length squared, width, and thickness of the sensor.
INTRODUCTION A key component of a biosensor is a signal transducer that converts physical, chemical, or biological interactions into measureable signals. Magnetostrictive materials that change their shape in response to an externally applied magnetic field have recently attracted attention for their potential use as sensor platforms in the surveillance of food safety. For millimeter-long, strip-shaped magnetostrictive materials with high magnetostriction coefficients, displacements along the longest dimension may reach tens of nanometers. Hence, by alternating the externally applied magnetic field at the right frequencies
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