The breakthrough discovery of a nanoscale optically gated ion channel protein, Channelrhodopsin 2 (ChR2), and its combination with a genetically expressed ion pump, Halorhodopsin, allowed the direct stimulation and inhibition of individual action potentials with light alone. This work reports developments of ultra-bright elec tronically controlled optical array sources with enhanced light gated ion channels and pumps for use in systems to further our understanding of both brain and visual function. This work is undertaken as part of the European project, OptoNeuro.
Micro-LED arrays permit spatio-temporal control of neuron stimulation on sub-millisecond timescales. However they are disadvantaged by their broad spatial light emission distribution and low fill factor. We present the design and implementation of a projection and micro-optics system for use with a micro-LED array consisting of a 16x16 matrix of 25 μm diameter micro-LEDs with 150 μm centre-to-centre spacing and an emission spectrum centred at 470 nm overlapping the peak sensitivity of ChR2 and its testing on biological samples. The projection system images the micro-LED array onto micro-optics to improve the fill-factor from ~2% to more than 78% by capturing a larger fraction of the LED emission and directing it correctly to the sample plane. This approach allows low fill factor arrays to be used effectively, which in turn has benefits in terms of thermal management and electrical drive from CMOS backplane electronics. The entire projection system is integrated into a microscope prototype to provide stimulation spots at the same size as the neuron cell body (μ10 pm).
The rise of optogenetic neural stimulation has opened new opportunities for neuroprosthesis such as visual cortical
prosthesis, which necessitates an efficient delivery of light into the cortex. New forms of photosensitizing
channelrhodopsin are reducing the required light intensities for stimulation, but implantable systems need to be highly
efficient. Such efficiency calls for low loss in the transmission path, high coupling efficiency between the optic delivery
system and optical emitter, as well as emitting efficiency from the light emitting diode. In this paper, we perform
simulation results based on ray optics and illuminating theory as to the best strategy to attachment of optrode structures
to Gallium Nitride-μLED arrays so as to maximize the efficiency of light delivery to the target neural tissue.Our results
show that it is feasible to connect optrode elements and GaN-μLEDarrays for cortical stimulation and describe the
optimisation requirements.
The precise control of neural activity afforded by the use of light sensitive ion channels such as Channel Rhodopsin
(ChR2) offers neuroscientists the means to devise new experiments. In this paper we present the Optogenetic Neural
Stimulation (ONS) platform which enables complex in-vitro or ex-vivo investigation of neural activity. The platform is
based on micro-meter sized Light Emitting Diodes (LEDs) integrated onto a single Gallium Nitrite chip. Mounted onto a
microscope system, this system can be used to carry out experiments on networks of cells, or on sub-cellular regions of a
neuron with millisecond timing and micrometer resolution.
This paper highlights how the genetic incorporation of artificial opsins into the retina can lead to a new class of retinal prosthesis. We demonstrate the efficacy of incorporating channelrhodopsin into neuron cells in-vitro and show how that can be scaled to in-vivo. We show that we need typically 100mW/cm2 of instantaneous light intensity on the neuron in order to stimulate action potentials which results in 10W/cm2 required from the light source. We thus use GaN LED arrays to provide spatially controlled stimulation which is of sufficient brightness to stimulate the cells.
KEYWORDS: Neurons, Luminescence, Near field scanning optical microscopy, Aluminum, Near field optics, Optical fibers, Microscopes, Atomic force microscopy, Neurotransmitter release, Near field
A SNOAM system is capable of obtaining simultaneous topographic and optical images with a resolution beyond than the diffraction limit of far field optical imaging. Fluorescence tagging combined with optical resolutions of better than 100nm allow us to detect structures not possible with conventional microscopes. Also in contrast with electron microscopy SNOAM has the ability to look at biological structures in the liquid medium. Presently there is much interest in understanding the processes that lead to LTP in neuron synapses. LTP is widely associated with memory function in neurons. Hence, better understanding will lead to advances in medicine, as well as neuron-based memory and processing devices. Better understanding is also crucial to the development of neuron-electronic interfaces. In this research, neuron networks are grown on a patterned polylysine substrate. Polylysine is patterned using micro lithographic techniques. Neurons are extracted from the hippocampus of chick embryos, and are then grown on this pattern under standard sterile incubating conditions. The neurons are stimulated to release the neurotransmitter glutamate. The glutamate is then fluorescently imaged with Amplex-red SNOAM.
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