When it comes to recording and stimu­lating brain activity, scientists can rely on a formidable tool: light. An inter­national research team, coordinated by IIT – Istituto Italiano di Tecnologia – has developed nanometric light modulators that, fabricated on a micro­metric optical fiber, make the fiber capable of studying neuronal tissue in deep regions of the brain. The new approach lays the groundwork for an innovative type of minimally invasive neural probe that can be used to study the central nervous system. In perspective, the nano­modulators will be employed to study specific brain diseases, including brain tumors and epilepsy.

In Italy the inter­disciplinary team aimed at obtaining micro­metric structures which are capable of studying neuronal tissue in a detailed way by using light, i.e. through the incorporation of optical nano­modulators. To do this, scientists combined expertise in nanometer-scale fabrication and biomedical neuro-engi­neering, in order to exploit the physics of surface plasmon polaritons and create an inves­tigative tool that modifies and amplifies the way light can stimulate and monitor specific brain areas.

They started from a tapered optical fiber and then they equipped it with nano­structures that resonate in response to a light stimulus introduced by the fiber itself into deep brain regions. The nano­structures were created by coating the probe microscopic tip with a thin layer of gold. Then, using a gallium ion beam as a chisel, they shaped a grid of nanoscopic optical elements, consisting of 100 nanometer thin lines, whose charac­teristics were validated in a series of micro­scopy and optical spectro­scopy experiments.

Thanks to this fabri­cation method, it was possible to obtain a tool which permits to control both the probe light beam modu­lation and the local electric field acting on surfaces comparable to the size of brain cells. Researchers may be able, then, to study the inter­action between the light beam and neuronal structures, even in the deepest areas of the brain. 

The possi­bility of creating such implantable plasmonic systems offers a new perspective in the study of the central nervous system: the ampli­fication produced by the nano­structures is intended to be an efficient tool for detecting the biochemical and cellular structure alterations underlying the origin of several neural disorders.

Therefore, the part of the inter­national team based in Spain is focusing on the application it may have. Experimental researchers at the Consejo Superior de Investi­gaciones Cientificas CSIC led by Liset M de la Prida are working to apply these probes in the study of post-traumatic epilepsy and neuro­degenerative diseases, such as Alzheimer's disease. While, the Brain Metastasis Group led by Manuel Valiente at the Centro National de Inves­tigaciones Oncologicas CNIO will investigate the use of this new technology to distinguish primary from metastatic tumors, whose treatments are different, as well as the use of light to permea­bilize the blood-brain barrier, allowing anti-tumour drugs to pass through the vascular barrier. (Source: IIT)

Reference: F. Pisano et al.: Plasmonics on a Neural Implant: Engineering Light–Matter Interactions on the Nonplanar Surface of Tapered Optical Fibers, Adv. Opt. Mat. 10, 2101649 (2022); DOI: 10.1002/adom.202101649

Link: Center for Biomolecular Nanotechnologies CBN, Istituto Italiano di Tecnologia IIT, Lecce, Italy