Brain is one of the most temperature sensitive organs. Besides the fundamental role of temperature in cellular metabolism, thermal response of neuronal populations is also significant during the evolution of various neurodegenerative diseases. For such critical environmental factor, thorough mapping of cellular response to variations in temperature is desired in the living brain. So far, limited efforts have been made to create complex devices that are able to modulate temperature, and concurrently record multiple features of the stimulated region. In our work, the in vivo application of a multimodal photonic neural probe is demonstrated. Optical, thermal, and electrophysiological functions are monolithically integrated in a single device. The system facilitates spatial and temporal control of temperature distribution at high precision in the deep brain tissue through an embedded infrared waveguide, while it provides recording of the artefact-free electrical response of individual cells at multiple locations along the probe shaft. Spatial distribution of the optically induced temperature changes is evaluated through in vitro measurements and a validated multi-physical model. The operation of the multimodal microdevice is demonstrated in the rat neocortex and in the hippocampus to increase or suppress firing rate of stimulated neurons in a reversible manner using continuous wave infrared light (λ = 1550 nm). Our approach is envisioned to be a promising candidate as an advanced experimental toolset to reveal thermally evoked responses in the deep neural tissue.

Infrared neuromodulation (INM) is a branch of photobiomodulation techniques, which offers direct or indirect control of cellular activity through elevation of temperature in a spatially confined region of the target tissue. Research on INM, started around one and a half decade ago, is gradually gaining attention of the neuroscience community, as numerous experimental studies give evidence of the safe and reproducible excitation and inhibition of neuronal firing in both in vitro and in vivo conditions. However, its biophysical mechanism is not fully understood, several engineered interfaces have been created to perform infrared stimulation in both the peripheral and central nervous system. In this review, we first summarize recent applications and present knowledge on the effects of INM on cellular activity, and provide an overview on technical approaches to deliver infrared light to cells and to interrogate the optically-evoked response. Micro-and nanoengineered interfaces to investigate the influence of infrared neuromodulation will be also described in details.

The proposed multifunctional tool is envisioned to broaden our knowledge on the role of the thermal modulation of neuronal activity in both cortical and deeper brain regions.

The phenomena resemble some features of in vivo separation of living tissue from the implanted artificial material, providing an in vitro model for studying immune response.

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Infrared neuromodulation is an emerging technology in neuroscience that exploits the inherent thermal sensitivity of neurons to excite or inhibit cellular activity. Since there is limited information on the physiological response of intracortical cell population in vivo including evidence on cell damage, we aimed to create and to validate the safe operation of a microscale sharp-tip implantable optrode that can be used to suppress the activity of neuronal population with low optical power continuous wave irradiation. Effective thermal cross-section and electric properties of the multimodal microdevice was characterized in bench-top tests. The evoked multi-unit activity was monitored in the rat somatosensory cortex, and using NeuN immunocytochemistry method, quantitative analysis of neuronal density changes due to the stimulation trials was evaluated. The sharp tip implant was effectively used to suppress the firing rate of neuronal populations. Histological staining showed that neither the probe insertion nor the heating protocols alone lead to significant changes in cell density in the close vicinity of the implant with respect to the intact control region. Our study shows that intracortical stimulation with continuous-wave infrared light at 1550 nm using a sharp tip implantable optical microdevice is a safe approach to modulate the firing rate of neurons.

Abstract:Nanostructured silicon surfaces like black-silicon (b-Si) are of great interest in current sensor technology. This paper presents an alternative method to fabricate b-Si in poly-silicon thin film prepared on pre-deposited insulation layer in order to open new door to the integration of silicon nanograss in biosensor application as sensing or seed layer. In our experiment, black poly-silicon (BPS) is formed in LPCVD deposited poly-silicon thin film by deep reactive ion etching (DRIE) at cryogenic temperature in SF 6 +O 2 plasma. Etching parameters like temperature, O 2 flow and RF power is varied and morphology of the resultant thin film is analyzed by scanning electron microscopy. The fabricated samples are subjected to a comparative investigation, which contained pillar density, directionality, etch rate and loading effects. The effect of the grain size of poly-silicon layer is analyzed and compared to samples micromachined in single-crystalline silicon (c-Si). We found that fabrication parameters of BPS morphology significantly differ from that of conventional b-Si realized in c-Si substrate. A simple application example of our BPS layer for increasing specific surface area of potential sensors is also demonstrated. As far as we know, this is the first demonstration and systematic study of b-Si fabrication in poly-silicon thin film.

Infrared neural stimulation is a promising medical technique using pulsed infrared light for generating temperature-controlled firing of neurons. A combined optical and thermal model of a stimulating microtool-or so-called optrode-has been developed to investigate the amount, the spatial distribution, and the temporal behavior of the thermal excitation. Ray tracing and Fourier optics were used to describe the propagation and scattering of light in the optrode, and the finite element method was applied to model heat transfer. The scattered intensity distribution profiles were calculated based on measured surface roughness of the device and were integrated into the ray optics model. As a validation of the optical model, the simulated and measured values of the light efficiency of the microoptical system are compared. The temperature rise of the brain tissue during the infrared stimulation was estimated using the combined model. Using 30 mW total power and a single 100 ms pulse, the excitation resulted in a temperature rise of 3°C of the brain tissue. The spatial and temporal distributions of the tissue temperature are discussed in the paper. The proposed combined model is an efficient tool for the investigation and optimization of the stimulation process and for further development of the optrode configuration.