Optogenetics - LED light Switch for neurons
The OptoFlash can output >30mW/mm2 from the end of a 200um fibre.
The Cairn Optoflash is the latest member of the Cairn OptoLED family. It uses our established LED head, fibres and microscope coupling designs, but is optimised for short-term intense illumination. This makes it particularly suitable for the photoactivation of “caged” neurotransmitter or other compounds, and for the important emerging application of channel rhodopsin activation.
The maximum current through an LED is generally limited by thermal considerations. Efficient heat removal from the device is only a partial solution, as the thermal resistance between the LED chip and its packaging always constitutes a significant bottleneck. Even so, the chip temperature rise on application of current still takes some milliseconds, so for illumination periods on this timescale, currents substantially higher than the steady-state maximum can safely be passed.
All our LED heads contain protection networks to limit both the transient and steady-state current to safe levels for that particular device. The LED heads intended for this particular application have had their protection networks optimised for short-term illumination periods, so as to maximise the intensity during a flash.
- Flash photolysis
- Flash duration controllable from 50μsec to 100msec by internal timer
- Duration of abritrary length via external control
- Flash rise and fall times less than 0.1μsec
- Optical monitor output with optional optical feedback
- Coupling system for optical fibres up to 1mm diameter
>30mW/mm² using a 200μm fibre when continuously driven by 470 LED
Protection network allows at least 2x over-driving for short pulses
Above is an LED head with direct coupling to fibre
Images courtesy of - Ed Boyden, McGovern Institute for Brain Research at MIT, Sputnik Animation
"Our need was to stimulate an isolated photoreceptor cell with sufficient light intensity to isomerize nearly all the photopigment molecules, and do so with the shortest flash duration possible: this would synchronize all such events, summate their electrical effects to maximize detectabililty, and avoid overlap with the photocurrent that is elicited only a few milliseconds later. Even the fastest electromechanical shutters proved inadequate for this task, while discharge flash lamps produced unacceptable electrical interference. We were pleased that the OptoFlash could pump enough photons within a sub-millisecond flash to even saturate rhodopsin, maintaining an excellent intensity control and defined time course."
Enrico Nasi - Cellular dynamics, Woods Hole, MBL