Magneto-mechanical trapping systems for biological target detection

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We demonstrate a magnetic microsystem capable of detecting nucleic acids via the size difference between bare magnetic beads and bead compounds. The bead compounds are formed through linking nonmagnetic beads and magnetic beads by the target nucleic acids. The system comprises a tunnel magneto-resistive (TMR) sensor, a trapping well, and a bead-concentrator. The TMR sensor detects the stray field of magnetic beads inside the trapping well, while the sensor output depends on the number of beads. The size of the bead compounds is larger than that of bare magnetic beads, and fewer magnetic beads are required to fill the trapping well. The bead-concentrator, in turn, is capable of filling the trap in a controlled fashion and so to shorten the assay time. The bead-concentrator includes conducting loops surrounding the trapping well and a conducting line underneath. The central conducting line serves to attract magnetic beads in the trapping well and provides a magnetic field to magnetize them so to make them detectable by the TMR sensor. This system excels by its simplicity in that the DNA is incubated with magnetic and nonmagnetic beads, and the solution is then applied to the chip and analyzed in a single step. In current experiments, a signal-to-noise ratio of 40.3 dB was obtained for a solution containing 20.8 nM of DNA. The sensitivity and applicability of this method can be controlled by the size or concentration of the nonmagnetic bead, or by the dimension of the trapping well.

If biological targets are present, they link magnetic beads and fluorescent beads. This results in less magnetic beads to be on the surface of magnetic sensor, causing a smaller signal, thus biological targets are detected.

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The authors wish to thank Dr. Filipe Cardoso of INESC Microsistemas & Nanotechnologias (INESC MN) for his help with the TMR sensor fabrication. The authors wish to thank Mr. Xiang Yu of KAUST Microwave Lab for his help with the measurement setup.

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Correspondence to Fuquan Li.

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Li, F., Kodzius, R., Gooneratne, C.P. et al. Magneto-mechanical trapping systems for biological target detection. Microchim Acta 181, 1743–1748 (2014) doi:10.1007/s00604-014-1241-6

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  • Magnetic biosensor
  • Magnetic beads
  • Nucleic acid detection
  • Trapping well