Neural Probes with Integrated Temperature Sensors for Monitoring Retina and Brain Implantation and Stimulation

Gold (Au) resistive temperature sensors were integrated on flexible polyimide-based neural probes to monitor temperature changes during neural probe implantation and stimulation. Temperature changes were measured as neural probes were implanted to infer the positions of the neural probes, and as the retina or the deep brain region was stimulated electrically. The temperature sensor consisted of a serpentine Au resistor and surrounded by four Au electrodes with 200 and $400~\mu \text{m}$ diameter (dia.). The Au temperature sensors had temperature coefficient of 0.32%, and they were biocompatible and small in size. In vivo measurements of temperature changes during implantation and stimulation were carried out in the retina and deep brain region in rats. The desired implantation position was reached when temperature measured by the sensor increased to the calibrated level and became stable. There was no temperature increase when low level stimulation current of 8 and $13~\mu \text{A}$ each for the two 200- and 400- $\mu \text{m}$ -dia. electrodes, respectively, were applied. When higher level stimulation current of 100 and $200~\mu \text{A}$ each were applied to the two 200- and 400- $\mu \text{m}$ -dia. electrodes, respectively, maximum temperature increases of 1.2 °C in retina and 1 °C in deep brain region were found.