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Measuring brain activity with magnetoresistive sensors integrated in micromachined probe needles

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Abstract

An alternative neuroscience tool for magnetic field detection is described in this work, providing both micrometer-scale spatial resolution and high sensitivity to detect the extremely small magnetic fields (nT range) induced by the ionic currents flowing within electrically active neurons. The system combines an array of magnetoresistive sensors incorporated on micro-machined Si probes capable of being inserted within the brain current sources. The Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. The probe shafts are formed by double-sided deep reactive ion etching on a double-side polished silicon wafer. The shafts typically have the dimensions 1.2 mm × 40 μm × 300 μm and end in chisel-shaped tips with an incorporated magnetoresistive sensor with dimensions of 30 μm × 2 μm. An accompanying interconnect flexible cable is glued and wirebonded enabling precise and flexible positioning of the probes in the neural tissue. Our analyses showed sharply defined probes and probe tips. The electrical and magnetic behavior of the sensors was verified, and a preliminary test with brain slices were performed.

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Acknowledgements

The work of J. Amaral was supported in part by FCT projects NANO/NMED-SD/0140/2007, PTDC/EEA-ELC/108555/2008 and PTDC/CTM-NAN/110793/2009 and by the FCT Ph.D. grant SFRH/BD/45488/2008. INESC-MN acknowledges FCT funding through the Associated Lab-Instituto de Nanotecnologias.

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Authors and Affiliations

  1. Institute for Nanosciences and Nanotechnologies, INESC-MN, Lisbon, Portugal

    José Amaral, Susana Cardoso & Paulo Freitas

  2. Instituto Superior Técnico, Universidade Técnica de Lisboa, Lisbon, Portugal

    José Amaral, Tiago Costa, Susana Cardoso & Paulo Freitas

  3. International Iberian Nanotechnology Laboratory, Braga, Portugal

    João Gaspar

  4. School of Health Sciences, Life and Health Sciences Research Institute, University of Minho, Braga, Portugal

    Vitor Pinto & Nuno Sousa

  5. ICVS/3B’s—PT Government Associate Laboratory, Braga/Guimarães, Portugal

    Vitor Pinto & Nuno Sousa

  6. INESC-ID, Lisbon, Portugal

    Tiago Costa

Authors
  1. José Amaral
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  2. João Gaspar
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  3. Vitor Pinto
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  4. Tiago Costa
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  5. Nuno Sousa
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  6. Susana Cardoso
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  7. Paulo Freitas
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Correspondence to José Amaral.

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Amaral, J., Gaspar, J., Pinto, V. et al. Measuring brain activity with magnetoresistive sensors integrated in micromachined probe needles. Appl. Phys. A 111, 407–412 (2013). https://doi.org/10.1007/s00339-013-7621-7

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  • DOI: https://doi.org/10.1007/s00339-013-7621-7

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