Stay-on-target: a sensortile based micropositioning system

When analyzing biological samples, measurement probe placement is of critical importance, as biological signals are typically characterized by small amplitudes, and thus a close proximity to the source of the aforementioned signal is necessary to maximize the signal to noise ratio. In this work, we present the Stay-on-Target (SoT): a low-cost, micrometrically precise, fully motorized, semi-automatic positioning system developed for manipulation of a needle-shape magnetoresistive probe within a sample of biological tissue. The proposed system is composed of three units – the user interface (with real-time microscopy video feed), the control module and the micropositioning module. This last module is supported by the ST Sensortile wireless sensing module, providing accelerometer, gyroscope and magnetometer data, as well as environmental parameters (temperature, humidity and pressure). Two algorithms were developed, taking advantage of the accelerometer and magnetometer data to automatically determine needle angle with a precision below 2º and a precision of 90 μm in what concerns sample surface detection. Finally, a needle penetration is demonstrated on an agarose sample, with a magnetoresistive based sensing probe used for in-vitro neuroscience experiments.