Arsenic Prototype 4.0

Principles

The Arsenic prototype v4.0 is the Winter School 2016 kit version of prototype 3.0.

The basis of the prototype remains the same - the bioreporter, a GMO bacteria expressing eGFP (Green Fluorescent Protein) is incubated with a water sample, where the fluorescence is detected optically and can be quantified in order to measure the concentration of Arsenic in the water

A vial containing the water sample we want to test is positioned on a socket through which a fluorescent excitation LED (blue 488nm for eGFP) passes.
GFP absorbs this blue light (λ=475 nm) and emits green light (λ=504 nm) which is detected by a photosensor on which the light is concentrated with the help of two lenses that avoid loss of intensity
A long-pass filter allow only the signal eGFP fluorescence to reach the photosensor

Moreover, a red LED was added to measure the transmittance, which can be converted into turbidity. The measurement of turbidity will allow us to normalize our results.

A red LED is placed in-line with the photosensor

We use an arduino to take the measurements, and we have a liquid crystal display (LCD) to read out the numbers.
With these measures, compared against a standard curve of water containing known arsenic concentrations, one can determine the concentration of arsenic in the sample and so know if the water is drinkable or not.

In summary, the most current version consists of:

   lasercut chassis
   blue LED for eGFP fluorescence excitation at 90 degrees from detector
   red LED for transmittance measurements in line with detector
   vial holder matching the vial approved by the Swiss authorities
   light to frequency detector
   a filter to block excitation light
   LCD screen read out
   based on the arduino

Materials

Plastic Lens Biconvex (Knight Opticals)
510nm long pass acrylic filter (Knight Opticals)

You can find the bill of materials here:

Step by Step Buildling

Laser Cutting the Inner Pieces

at chez hackuarium - laser cutter model: Keyland KQG-1060 120W CO2 laser cutter

Cutting Parameters for Material: HDF (MDF)
	mode	speed	power	scan mode	interval
Groove LED (fluo)	scan	50 (100)	35	x_unilat	0.1
3mm board	cut	15	100
Text and Logo	scan	250 (100)	25	x_unilat	0.3
Groove Lens	scan	50	12	x_unilat	0.1
2mm board	cut	35	100

Results

high-density fiberboard HDF
medium-density fiberboard MDF

Assembling the Electronics

There are four PCBs for:

Blue LED (for the eGFP excitation)
LCD screen
Red LED (for the transmittance)
Light to frequency meter (to detect the light)

Each of the PCBs except the LCD screen PCB are fixed onto the lasercut boards using M3 screws.

Soldering and Mounting

Blue LED

LCD screen

Red LED

1. first mount the red LED - short leg = negative
2. next, the pins, long pins same side as the LED
3. ready to mount on the board
4. mounted, view from the PCB side
5. mounted, view from the LED side

light to frequency meter

LFD 1.JPG

1. place the legs of the light to frequency detector (LFD) in the PCB without bending or soldering
2. use the particle board to align the 'eye' of the LFD
3. solder the LFD and the long pins same side as the LFD
4. back of the soldered PCB aligned with the particle board
5. place a washer to account of the LFD thickness
6. mounted, view from the PCB side
7. mounted, view from the LFD side