Bio-mimetic synthetic cell hydrogel magnetometer.

We present a bio-inspired hydrogel magnetometer where the cell potential (V ) between two hydrogels is used to measure an external magnetic field. Ferromagnetic particles located in the hydrogels move in response to the external field and change the V (sensitivity ~ 3.7 V T). As the field becomes larger than a critical field B (~38 mT), these particles puncture the hydrogel boundary shorting out the concentration gradient region and abruptly reducing the V (sensitivity ~ 23.5 V T). In this regime, the V behaves similar to the neuron firing. In subsequent measurement cycles, the particles remain in punctured holes and the sensor behaviour is neuron-like with lower sensitivity (~20 V T). V also changes as a function of pressure (8 mV kPa) and temperature (2 mV K). After 4 h, the ionic concentration gradient diminishes in the device, and similar to biological cell fatigue, V decreases and can be recharged with many different techniques.