LED Optrode with Integrated Temperature Sensing for Optogenetics

Abstract

In optogenetic studies, the brain is exposed to high-power light sources and inadequate power density or exposure time can cause cell damage from overheating (typically temperature increasing of 2 ∘C). In order to overcome overheating issues in optogenetics, this paper presents a neural tool capable of assessing tissue temperature over time, combined with the capability of electrical recording and optical stimulation. A silicon-based 8 mm long probe was manufactured to reach deep neural structures. The final proof-of-concept device comprises a double-sided function: on one side, an optrode with LED-based stimulation and platinum (Pt) recording points; and, on the opposite side, a Pt-based thin-film thermoresistance (RTD) for temperature assessing in the photostimulation site surroundings. Pt thin-films for tissue interface were chosen due to its biocompatibility and thermal linearity. A single-shaft probe is demonstrated for integration in a 3D probe array. A 3D probe array will reduce the distance between the thermal sensor and the heating source. Results show good recording and optical features, with average impedance magnitude of 371 kΩ, at 1 kHz, and optical power of 1.2 mW·mm−2 (at 470 nm), respectively. The manufactured RTD showed resolution of 0.2 ∘C at 37 ∘C (normal body temperature). Overall, the results show a device capable of meeting the requirements of a neural interface for recording/stimulating of neural activity and monitoring temperature profile of the photostimulation site surroundings, which suggests a promising tool for neuroscience research filed.

A current-mode system to self-measure temperature on implantable optoelectronics

“…Prior to this work, some resistor and RTD-based temperature sensors are reported to monitor the temperature in brain, retina and myocardium [11–14]. Goncalves et al reported an optrode with an integrated temperature sensor based on RTD [14]. The implemented 3D probe has positioned RTD on the opposite side of the LED to reduce the distance between the heating source (LED) and the thermal sensor (RTD).…”

“…Table 3 compares the designed temperature sensors with resistor-based temperature sensors for in vivo application, whereas only one is integrated within the optrode with LEDs for optogenetics application [14]. Our achieved temperature range is based on the measured reverse current change versus temperature variation, which is dependent on the applied bias and mainly the LED type.…”

“…We, therefore, went further and explored the possibility of utilizing a temperature-sensitive device to monitor the LED surface temperature. Adding a resistance temperature detector (RTD) or thermistor would add to the required space on implantable devices [10–14]. As such, we explored the use of LED as their own temperature sensors by using the LED reverse current as a junction temperature-sensitive parameter (TSP).…”

Wireless and battery-free technologies for neuroengineering

“…202 ) and ReaCHR 203 , and halorhodopsin 204 ). In pulsed-mode operation, the maximum steady-state temperatures at the interface with the tissue are less than a few tenths of a degree Celsius 102 , which is well below the safety thresholds (2-5 °C) for irreversible tissue damage 205,206 , the 2 °C limit for neurostimulators 207 and the approximate 1 °C limit for thermal neuromodulation 208 . Such µ-ILEDs have electrical operating requirements that can be satisfied by a range of wireless power sources.…”

Editorial for the Special Issue on Neural Electrodes: Design and Applications

“…To provide enhanced control during optogenetic studies, Goncalves et al [16] describe a hybrid device combining optical stimulation and neural recording, which is capable of monitoring the heat generated during light exposure. A proof-of-concept device, with double-sided function: on one side, an optrode with LED-based stimulation and Pt recording sites on one side of the probe and with a Pt-based thin-film thermoresister for temperature measurement on the opposite side, was fabricated and characterized.…”