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This paper reports on the development, characterization and in vivo validation of compact optical neural probes. These novel intracerebral devices comprise micro light-emitting diodes ( μLEDs) integrated along their slender probe shanks with up to 20  μLEDs per device. Blue light with a peak wavelength of 455 nm is emitted from circular apertures 100  μm in diameter. The μLEDs are structured on GaN-on-sapphire wafers and subsequently transferred onto silicon (Si) carrier wafers. The wafer-scale transfer process provides the opportunity to process the functional GaN layer stack from both sides and hence enables maximizing the efficiency of the μLEDs. Combined with standard MEMS fabrication processes for Si, linear μLED arrays with small inter- μLED distances are achieved on thin probe shanks with cross-sections measuring [Formula: see text]. Devices are interconnected using highly flexible polyimide cables in order to mechanically decouple them from the peripheral electronics during in vivo experiments. Assembled probes emit a peak optical radiant flux of 440  μW (emittance 56 mW mm -2 ) at 5 mA driving current. Thermal characterization of test probes reveals a temperature increase of 1.5 K measured using an integrated thermistor. Electrical functionality stress tests have been carried out to evaluate the device passivation against the physiological environment. It is estimated to endure at least 48 h during continuously pulsed μLED operation. A compact driving circuitry enables low-noise μLED operation in in vivo optogenetic experiments. The radiant flux necessary to elicit an acceptable neuronal response is determined between 1.36  μW and 17.5  μW. Probe validation successfully demonstrates the layer-specific stimulation in the cortex in multiple in vivo trials.

This article reports on the development, i.e., the design, fabrication, and validation of an implantable optical neural probes designed for in vivo experiments relying on optogenetics. The probes comprise an array of ten bare light-emitting diode (LED) chips emitting at a wavelength of 460 nm and integrated along a flexible polyimide-based substrate stiffened using a micromachined ladder-like silicon structure. The resulting mechanical stiffness of the slender, 250-μm-wide, 65-μm-thick, and 5- and 8-mm-long probe shank facilitates its implantation into neural tissue. The LEDs are encapsulated by a fluropolymer coating protecting the implant against the physiological conditions in the brain. The electrical interface to the external control unit is provided by 10-μm-thick, highly flexible polyimide cables making the probes suitable for both acute and chronic in vivo experiments. Optical and electrical properties of the probes are reported, as well as their in vivo validation in acute optogenetic studies in transgenic mice. The depth-dependent optical stimulation of both excitatory and inhibitory neurons is demonstrated by altering the brain activity in the cortex and the thalamus. Local network responses elicited by 20-ms-long light pulses of different optical power (20 μW and 1 mW), as well as local modulation of single unit neuronal activity to 1-s-long light pulses with low optical intensity (17 μW) are presented. The ability to modulate neural activity makes these devices suitable for a broad variety of optogenetic experiments.

We report on the concept, development, and geometrical, optical as well as electrical characterization of the first three-dimensional (3D) optrode. This new device allows to optically interact with neuronal cells and simultaneously record their response with a high spatial resolution. Our design is based on a single-shank optical stimulation component and a multi-shank recording probe stacked together in a delicate assembly process. The electrical connection of both components is ensured by using flexible polyimide (PI) ribbon cables. The highly accurate relative positioning and precise alignment of the optical and electrical components in 3D with an optical output power at 460 nm well above 5 mW/mm2 and an all-electrical interface makes this device a promising tool for optogenetic experiments in neuroscientific research.

Optical stimulation and inhibition of neural tissue is a promising neuroscientific method to control neural activity in so-called optogenetic experiments. This work illustrates the development of an implantable neural probe with an array of 10 integrated light emitting diode (μLED) chips emitting at a wavelength of 460 nm. The probe is suitable for experiments requiring a depth-controlled optical stimulation at multiple sites. The μLEDs are flip-chip-bonded to a polyimide cable stiffened by a micro-machined ladder-shaped silicon element for robust insertion into neural tissue. The optical operation of the 250-μm-wide, 65-μm-thick and up to 8-mm-long devices and their stability in an electrophysiologically relevant electrolyte is demonstrated. This tool paves the way for a large variety of optogenetic experiments in neuroscience. [ABSTRACT FROM AUTHOR]