GIN - Graphene-based Interfaces for Neuroapplications
Table of contents
Project description
A very popular theme in science fiction is that of a cyborg, a hybrid of a living organism and machine. Interestingly, it is becoming a reality. In fact, neuroprosthetic devices already exist, such as cochlear implants, which convert sound to electrical signals transmitted to cochlear nerve. To this extent, neuroscience research focuses on the development of a brain-machine interface, which will enable the direct communication of computers with the brain, aiming on restoring vision, hearing, movement and cognitive functionality. Currently, microelectrode arrays are used as interfaces. They consist of an array of sharp metal needles, enabling contact to neural cells. However, such stiff metal needles are not fully compatible with soft and elastic cells, the number of electrodes is limited, typically ranging from tens to a hundred, and the sensitivity of signal measurement is not high enough. Nanoscience may provide novel key technology to overcome current limitations for connecting biological matter with machines. In particular, graphene has many properties that make it a promising candidate for the development of new solutions. Graphene has extremely high charge carrier mobility, it is flexible, biocompatible, and there have been many proof-of-principle demonstrations of graphene devices such as field effect transistors and photodetectors. Recently, mapping of mouse brain activity was achieved by an array of 16 microtransistors based on graphene.
During the last couple of years, we have developed laser modification techniques to oxidize graphene and to fabricate 3D structures simply by using a pulsed laser. Indeed, features well below a micrometer can now be patterned with tight focusing. This laser fabrication toolbox enables the optical fabrication of graphene-based devices. In this project, we aim at developing an interface between nerve cells and machines based on graphene.This requires a multidisciplinary approach towards:
a) The fabrication of graphene transistor devices by laser fabrication techniques.
b) Their functionalization with antibodies showing specific affinity to nerve cells.
c) The introduction of soft materials (gels) on the device´s interface to mimic the properties of the brain´s extracellular matrix and enable the attachment and proliferation of nerve cells.
The final target is to measure electrical and chemical signals from nerve cells with a large array of graphene transistors. This requires theoretical work for understanding the properties of optically modified graphene and for designing the devices and experimental work for constructing and testing the devices.
Results
1. Sitsanidis, Efstratios D.; Schirmer, Johanna; Lampinen, Aku; Mentel, Kamila K.; Hiltunen, VesaMatti; Ruokolainen, Visa; Johansson, Andreas; Myllyperkiö, Pasi; Nissinen, Maija; Pettersson, Mika. Tuning protein adsorption on graphene surfaces via laser-induced oxidation. Nanoscale Advances, 2021, DOI: 10.1039/D0NA01028F
An approach for controlled protein immobilization on laser-induced two-photon (2P) oxidation patterned graphene oxide (GO) surfaces is described. Selected proteins, horseradish peroxidase (HRP) and biotinylated bovine serum albumin (b-BSA) were successfully immobilized on oxidized graphene surfaces, via non-covalent interactions, by immersion of graphene-coated microchips in the protein solution. The effects of laser pulse energy, irradiation time, protein concentration and duration of incubation on the topography of immobilized proteins and consequent defects upon the lattice of graphene were systemically studied by atomic force microscopy (AFM) and Raman spectroscopy. AFM and fluorescence microscopy confirmed the selective aggregation of protein molecules towards the irradiated areas. In addition, the attachment of b-BSA was detected by a reaction with fluorescently labelled avidin-fluorescein isothiocyanate (Av-FITC). In contrast to chemically oxidized graphene, laser-induced oxidation introduces the capability for localization on oxidized areas and tunability of the levels of oxidation, resulting in controlled guidance of proteins by light over graphene surfaces and progressing towards graphene microchips suitable for biomedical applications.
2. Mentel, Kamila K.; Manninen, Jyrki; Hiltunen, Vesa-Matti; Myllyperkiö, Pasi; Johansson, Andreas; Pettersson, Mika. Shaping graphene with optical forging: from a single blister to complex 3D structures. Nanoscale Advances, 2021, 3 (5), 1431-1442.
Properties of graphene, such as electrical conduction and rigidity can be tuned by introducing local strain or defects into its lattice. We used optical forging, a direct laser writing method, under an inert gas atmosphere, to produce complex 3D patterns of single layer graphene. We observed bulging of graphene out of the plane due to defect induced lattice expansion. By applying low peak fluences, we obtained a 3D-shaped graphene surface without either ablating it or deforming the underlying Si/SiO2 substrate. We used micromachining theory to estimate the single-pulse modification threshold fluence of graphene, which was 8.3 mJ cm−2, being an order of magnitude lower than the threshold for ablation. The control of exposure parameters allowed the preparation of blisters with various topographies. The optically forged structures were studied with atomic force microscopy and Raman spectroscopy. Optically forged blisters act as building blocks in the formation of more complex structures. We found a simple geometric rule that helps to predict the shape of complex patterns which are created by the overlapping multiple exposures. Optical forging enables writing of extended patterns with diffraction unlimited features, which makes this method promising in the production of nanodevices with locally induced surface modifications.
