How construct a LED Array?

The following information contains the steps that were done by the UNAM-Genomics Team for iGEM 2010 in order to construct an improvised light dispositive to irradiate bioluminiscent cells.

Introduction
Synthetic Biology has been enabling changes in all bio-domains, one such being communication. Cellular communication has relied since time immemorial on chemical messengers to exchange information.

In their iGEM 2010 project, team UNAM-Genomics Mexico had the goal of rendering the chemical barrier deprecated by using a non-chemical messenger: photons. These will transport information between cells that have been designed to sense and emit light, thus creating a photon-based inter-cellular communication system.

They decided to break down their devices into 3 module sub-classes: Reception, Emission, and Transmission. One of the most important things in the project is how the cell receives the information and processes it. The intensity of the answer is proportional to the level of the message, so is necessary to characterize the black magic box that occurs in the cell. I other words: {photons} -> {Black Box} -> {Pops} and vice versa.

A simple aproach to characterize the black box is to know how many photons are needed to turn on the system, and to evaluate the consequent level of the expression in the cell. We therefore, constructed a plate capable of irradiating differentially a set of cultures following a time guide.

To allow you to test our receptors for yourself in different conditions that are reported, or if you simply have a lot of free time in the lab, we report a do it yourself for our measuring device.

Requeriments
A LED is a a semiconductor light source used as an indicator lamp in many devices; furthermore they are increasingly used for lighting. Small size, an incredibly efficient emission, a good life time and do low resistivity (low operating temperatures) make them perfect for biological assays!!!

Another good thing about LEDs is the diversity of sizes, the 5mm fit perfectly to an ELISA black plate used to measure fluorescence. Knowing the ease of stacking for said plates, you can use two: one for the LED array and the other for the fluorescent strains. This holds two great advantages: the culture plate can be kept as sterile as desired, and changing it while keeping the irradiating one is extremely easy.

You may remember from a distant electronics class that the electrical current in a circuit passes trough all devices, and these generate resistance to the electron flux. By the law of Ohm, we need an efflux of electrons that can go trough all the LEDs without problems, so we require an energy transformer with high amperage to maintain all the LEDS with the same intensity.

Also you maybe want to use a triply perforated board to ease the organization, and a box painted black to reduce the external noise caused by visible light.

What do you need
Therefore, what you do need to replicate our device is:


 * Soldering kits (more kits means more hands)
 * 96 5mm 3v LEDs of the color that interests you
 * Switches to turn off/on each pair of LEDS
 * ELISA 96-well black plate
 * Electrical tape
 * Needle nose pliers
 * Triply perfored board, 12 by 8 holes
 * 4 meters of copper wire
 * An energy transformer (out 3V, 2A)
 * Patience :)

Early stages
In electronic parlance, the following diagram shows the works:



Negative Serpent
You need cut approximately 40 cm of clean wire to create the lead wire, a "serpent" that will cross between two rows of holes in the ELISA plate. Stick the sides with electrical tape to keep it in place and maneuver it with ease.

Position LEDs
You can start positioning the LEDs according to the diagram. They should be connected in parallel, by pairs, to the circuit to distribute all the charges. Remember that the longest arm of the LED is the positive one.

Connect Negative Ends
Use the pliers to form loops in the negative legs of the LEDs, maybe 2 mm of diameter, the loop will hold the copper wire which will be conected to the copper "serpent" in the ELISA plate. The bigger the hole, the easier it is getting the wire through, though the more difficult it is to secure the wire in place. Cut the copper wire into several 3 centimeter long segments. Then clean both ends, one 10mm up to connect to the plate, and the other 15mm to pass trough the loop of the LEDs.

Create Positive Ends
Create loops again, but now in the positive legs of the LEDs. Cut more copper wire into five centimeter long (or the long necessary to fit in a box) segments. Next clean both ends, one 5mm up to connect to the positive wire that is going to be in the up of the box, and the other 10mm to pass trough the loop of the LEDs.

Test & Weld
At this stage, you should be able to test all the conections with a charge of 3 volts. Connect ONLY ONE end of the serpentine copper wire's ends to the generator´s negative pole. Nothing should happen as the circuit is still open. Next connect one of the 5cm wires to the positive end of the generator. Only a pair should light up. If all pairs light up when you connect all wires, then the connections are correct. You should proced to weld all the LED conections.

The Board, Negative Serpent & Switches
Now you should put the perforated board in place. You need to pass trough the board all the positive wires. To perform this we recommend you pass one by one, and stick it to the board's outer side with electrical tape. Once the board is in place with many protruding positive wires, you will need a main positive cable. You can repeat the process for the negative serpentine to get a positive serpentine. Once this is in place, attack a switch to each of the protruding wires.

Connecting the Negative
To connect the switches to the positive serpent, cut copper wires as long needed. Keep in mind that the protruding wires and the wires you just cut should NOT come into contact, that's what the switches are for. Connect the wires you just cut to the positive serpent, next connect these to the switches. Test your switches! Only one pair should light up when a single switch is on. If they are functional, weld them. Test them again to make sure the welding is not accidentally connecting other wires.

Box it
Once you finish welding the wires, the plate is almost complete. The final stage is getting the assembly into the black box. Now just test the system: conect the down serpent to the negative pole and the up serpent to the positive pole, turn off/on all your LEDs.

For any question see the images. Also, you can email us:
 * Amhed M. Vargas Velazquez
 * Hector F Medina

More information

 * Log of our team experience From 22/06 to 27/06
 * The experiment and Technical issues
 * UNAM-Genomics iGEM 2010 Wiki