Quantitative Determination ofEscherichia Coliin Water Sources in the Environment Using a Surface Acoustic Wave Impedance System Modified with a Syringe Filter

A wireless bio-sensing microfluidic chip based on resonating 'μ-divers'

A magneto-elastic resonant 'micro-diver' system (MER-μDS) is proposed and developed for rapid liquid-phase detection of pathogens in a wireless way. The magneto-elastic micro-resonator (i.e., the μ-diver) is placed in the micro-chamber of the MER-μDS that is connected to the inlet/outlet for flow of the liquid analyte and a closed-loop micro-channel. After specific attachment of the analyte onto the μ-diver, the μ-diver is conveyed by the flow into the detection segment of the channel, around which a metal micro-coil is wound for both excitation resonance of the μ-diver and reading of its resonance frequency signal. After the pre-functionalized μ-diver captures the analyte and, then, is driven into the detection channel segment, the added mass induced resonant frequency shift can be wirelessly sensed by the coil. The micro-system features rapid and repeatable liquid-phase bio-sensing and the wireless signal readout scheme is favorable to real-time pathogen detection in liquid food, e.g., milk or juice, for food safety applications. An equivalent circuit model is established for design of the magneto-elastic μ-diver. After a bar-shaped μ-diver with length-extensional bulk-resonance mode is optimally designed and micro-fabricated, the MER-μDS is formed by micro-machining/assembling techniques. By placing a biotin-immobilized μ-diver into the wireless micro-sensing system, avidin-attached magnetic beads are detected to calibrate the mass sensitivity as 0.061 Hz pg(-1), which well confirms the modeling result. By using the antibody-immobilized μ-diver, PBS solution with an E. coli concentration of 10(2)-10(8) CFU mL(-1) is detected, resulting in a corresponding wireless f0-shift sensing signal of about 300-2300 Hz and a limit of detection of 10(2) CFU mL(-1). Food safety application potential of the MER-μDS technique is proven by detection of E. coli added to orange and apple juices (E. coli concentration: 10(4)-10(8) CFU mL(-1)).