Interfacing of neurons with layer -by -layer thin films of semiconductor nanomaterials.

Abstract

The stimulation of neuron cells selectively, either by position or size and sending action potentials unidirectionally via a biocompatible interface is of considerable interest for treatments of neuronal injuries and sensory deficits, specially, stimulating visual cortex with high density surface electrodes. The use of electrical current directly to stimulate neurons through metallic or non-metallic electrodes presents several challenges such as non selective stimulation, rigid invasive geometrical shapes and bioincompatibility. Further, the ideal electrodes are required to be in the same size as neuron cells for selective stimulation. Presented work was focused on developing a biocompatible and remotely controllable neuron/thin film interfaces which can stimulate neuron cells upon absorption of visible light or infrared radiation. Since unique optical and electrical properties of nanomaterials offer several advantages over conventional materials for neuron cell stimulation, semiconductor nanomaterials (i.e. HgTe nanoparticles and single wall carbon nanotubes) were selected for the fabrication of neural interfaces. LBL technique was used to fabricate thin films assemblies on ITO-coated glass substrates. The LBL thin films of nanomaterials were improved in terms of material properties and processing techniques for efficient photo conversion since stimulation strongly depends on the amount of current generated. Biocompatibility and accumulation of charge is the key for better interfacing and stimulation of neuron cells with LBL thin films. Hence, special biocompatible clay layers were deposited on LBL thin film assembly to improve biocompatibility and accumulation of charges on the interface. Generated action potentials of stimulated neuron cells were detected using voltage-clamped and atomic force microscopic (AFM) techniques. Further, a mathematical model was proposed to explain the diffusion dependant current generation behavior of LBL thin films in both aqueous and physiological electrolytes. The effect of internal concentration of redox species on the magnitude and shape with respect to diffusion across the LBL thin film interface was investigated in detail. Most importantly the effect of diffusion length of redox species on porous LBL thin films with nano-scale thickness was illustrated. Further this work was extended to explain the change of concentration profiles inside the LBL thin film with respect to surface coverage.