Optogenetics is a relatively new technology to achieve cell-type specific neuromodulation with millisecond-scale temporal precision. Optogenetic tools are being developed to address neuroscience challenges, and to improve the knowledge about brain networks, with the ultimate aim of catalyzing new treatments for brain disorders and diseases. To reach this ambitious goal the implementation of mature and reliable engineered tools is required. The success of optogenetics relies on optical tools that can deliver light into the neural tissue. Objective/Approach: Here, the design and manufacturing approaches available to the scientific community are reviewed, and current challenges to accomplish appropriate scalable, multimodal and wireless optical devices are discussed. Significance: Overall, this review aims at presenting a helpful guidance to the engineering and design of optical microsystems for optogenetic applications.

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 ${}^{\circ }$ 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 k $\mathsf{\Omega }$ , at 1 kHz, and optical power of 1.2 mW·mm ${}^{-2}$ (at 470 nm), respectively. The manufactured RTD showed resolution of 0.2 ${}^{\circ }$ C at 37 ${}^{\circ }$ 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.

Implantable active dense CMOS neural probes unlock the possibility of spatiotemporally resolving the activity of hundreds of single neurons in multiple brain circuits to investigate brain dynamics. Mapping neural dynamics in brain circuits with anatomical structures spanning several millimeters, however, remains challenging. Here, a CMOS neural probe advancing lateral sampling for mapping intracortical neural dynamics (both LFPs and spikes) in awake, behaving mice from an area >4 mm² is demonstrated. By taking advantage of SiNAPS technology modularity, an 8‐shank probe with 1024 recording channels arranged in regular arrays of 128 electrodes/shank with an electrode pitch <30 µm is realized. Continuous low‐noise recordings (spikes with 6.67 ± 1.02 µV_RMS) from all 1024 electrodes at 20 kHz/channel demonstrate the monitoring at high spatial and temporal resolution of a field of view spanning the 2D lattice of the entire mice hippocampal circuit, together with cortical and thalamic regions. This arrangement allows combining large population unit monitoring across distributed networks with precise intra‐ and interlaminar/nuclear mapping of the oscillatory dynamics.

A completely new approach for the fabrication of 3-axis thermal accelerometers is presented in this paper. Micromolded polystyrene micro-parts are assembled with polyimide membranes enabling the construction of thermal accelerometers. The use of polymers (polystyrene and polyimide) with low thermal conductivities improves the overall power consumption of the thermal accelerometer and enables a simple and low-cost fabrication process (no clean room infrastructure required). The accelerometer is composed of 4 polystyrene microinjected structural micro- parts (two identical top parts and two identical central parts) and three polyimide membranes (two identical z-axis membranes and a central membrane). The microinjected parts provide the mechanical support for the active elements that are placed on the membranes (the heater and the temperature sensors). Coupled 3D thermo-electric-fluidic FEM simulations show that current design has a sensitivity of 1.6°C/g in the X-Y directions and 0.2°C/g in the Z direction for a central heater temperature of 300°C