Chronology of the prototypes
Here is a chronology of our different prototypes :
Prototype 1 (2013)
The principe used is measuring the fluorescence at an angle of 90° from the light source.
The light from the LED passes through a lense to be focused and then through a filter, to only let the excitation wavelength pass through. That filtered light will excite the sample, which will emit at another wavelength and will then be detected. In general, photodiodes or photomultiplier are used as detectors, but they are quite expensive. That is why a digital camera is used as detector. Indeed, all camera contains an RGB filter, which can be used to detect only the range of wavelength of interest. A LED that emits at the needed range of excitation wavelength is used , to eliminate the presence of a filter.
For this device : two paperboard boxes sticked together with two holes for the camera and the LED are used. The box is closed so no external light would disturb the measurement. Inside, there is a horizontal place for the sample-holder and ouside we used an Arduino as the LED current source.
After testing, the device needs some improvements. For example, a lot of the components are outside of the box (like the LED and the camera), which makes it very difficult to take a fixed picture, because everything moves a little bit at each measure. The sample is positionned horizontally, which we discovered, is not the best orientation, because of light scattering, but also because we have to open the box for each sample. This is another factor that disturbs the system by making it move. Then we need a computer for the alimentation of the Arduino (that only acts as a battery).
So the improvements made :
- The addition of a battery to replace the Arduino and a switch, to be able to turn the LED on and off individually
- The fixation of the camera inside the device to obtain more precise pictures
- Putting the sample in a vertical position to allow an easiest change between different samples
Prototype 2 (2013)