The Fiberlight
Electrode and cells vary. If you fill neurons with fluorescent dyes like Alexa 488, it is difficult to judge how well the neuron is filled. While in some preparations you get away with attaching an appropriate filter to your stereo microscope, but this is not an option in Aplysia. The yellow tissue of Aplysia ganglia filters out to much blue light (the wavelength Alexa 488 is excited with) to use a transmissive illumination. Epi-illumination does the trick. The Fiberlight provides a weak, but cheap solution to the problem. It does in no way replace a fluorescence microscope, but provides enough light to judge how well a neuron is filled. No additional filters are necessary.
Figure 1: Bottom left: Small version, powered by three AAA batteries. Top left: Variable version that allows setting any ratio of blue and white light by turning the potentiometer knob. Top right: three wavelength version with switchable white, blue, and amber LED for viewing different dyes. Bottom right: Regular blue version with connector to power supply.
The Fiberlight consists of a battery holder, some current
regulating components (I use a 3.3V voltage regulator and a 150 Ohm
resistor), an appropriate LED, and a plastic "glass" fiber. I build
several different versions (Fig. 1). Most parts are available from Digikey:
| SBH-341AS-ND | large battery holder with switch (I modified these to hold only 3 AAA batteries. This gives you plenty of room for the other components.) |
| or SBH-331AS-ND | small battery holder (Everything fits in there, but it is a bit crowded) |
| 296-12722-5-ND | 3.3V regulator that doesn't require any additional components (It also allows you to connect the light to a power supply.) |
| 150XBK-ND | 150 Ohm 1/4W resistor to limit the current |
| A1700-5-ND | 5 meters of plastic "glass" fiber |
| A1703-ND | socket for the glass fiber / LED holder (with a bit of epoxy) |
| A1705-ND | plug for glass fiber |
Furthermore you will need 3 AAA batteries, some M2 screws (e.g. McMaster-Carr 92000A015, 91828A111, and 93475A195), a Dremel to drill the holes, a soldering iron, and a sharp blade to cut the plastic fiber. Epoxy glue is very helpful, too. In some models I put in a socket for a power supply. The supplies that come with the Newport motion controller 861 work great, but basically any 4-8V DC supply will do.
With only three components it should be pretty straight forward how to assemble them (Fig. 2). Hold the voltage regulator so that you can read what's written on it. From left to right, the pins are: input, ground, outout. The longer lead of the LED needs to be connected to +, the shorter to ground (try it out).
Figure 2: A 150 Ohm resistor limits the current. While the voltage regulator is clearly overkill if you only use batteries, it makes life easierin case you later decide to also use a power supply.
Figure 3 left: The bigger case with voltage regulator, resistor, and power adapter socket. Right: In the smaller case there is no room for the socket. The voltage regulator and resistor are under the yellow electric tape on the left side.
Putting everything in the battery holder it might look like Fig. 3. A Switch is already build into the battery case when you buy it. The glass fiber (which is made out of plastic) allows you to bring the light very close to you ganglion. You can pin its end in the dish, right next to the ganglion. Screw the "device mount" right next to the switch on the battery case (Fig. 4). If the LED is not held stable by its wires, you can also glue it into the mount. (The mounts are actually made for a different type of LEDs, hence are not ideal.) Put the plug on the fiber, cut it making sure not to cut into the clear fiber when removing the black jacket. Plug it in and you are done!
Figure 4: The "device mount" is crewed onto the battery case. The LED is held in its position by its wires.
The 2nd Generation
If a standard LED does not provide enought light for you, you can also build the fiberlight with a Luxeon LED from LUMILEDS. Their LEDs are incredibly bright, but also draw a lot of current (750mA and up). A heat sink as well as a power supply becomes therefore mandatory. Fig. 5 shows an example, driven from a laboratory power supply.
Figure 5: The 2nd generation version. A Luxeon Emitter is held between the black heat sink and the metal case. A high current voltage regulator reduces the voltage from a laboratory power supply to the right level.
The 3rd Generation
With blue LEDs being increasingly more powerful, the third generation light does not any longer require a fiber to focus the light on the area of interest. The Luxeon V LED provides plenty light to illuminate the complete speciment at very high levels (output: 48 lm; Fig. 6). For cell-killing applications it can be swapped with the Luxeon "Dental Blue" with 600 lm output and still affordable price tag. A FRAEN narrow beam lens / reflector in front of the LED controls the spread of light. LED, lens, a voltage regulator, and power resistor are mounted on a solid piece of aluminum. An additional heat sink is mounted on the back.
Figure 6: A Luxeon V LED with FRAEN lens/reflector is powerfull enought to illuminate the entire preparation. The "dental blue" variant provides the highest output, e.g. for cell-killing applications