Learning Thru Research: January 2017

Emelyne GAUDICHAU, Julien PICHON, Daphné GUENEE

@Lumos_Stupefix

C.elegans versus

VEML 6070

- A Biosensors project

Ever wanted to know the extend of the UV you’re exposed to but don’t have access to a UV sensor ? Well we have got the solution ! During the first week of the Biosensors, the Lumos_Stupefix team, composed of Emelyne, Daphné and Julien used a biological alternative that is the Caenorhabditis elegans.

In this blog post, we will try to show you which of the biological sensor and electronic sensor is the most precise to detect different intensities of UV light. For our project we decided to use a wavelength of 390 nm because previous researches have shown that C.elegans respond best to this wavelength.

For seven days we worked to see to what extent C.elegans are precise to detect the different intensities of UV light compared to the precision of the UV sensor. Before jumping in, here is some information about the sensors.

What is the biological sensor ?

C.elegans are micro-organisms also known as round worms. They are little transparent worms that mesure 1 mm and that live in the dark. C.elegans don’t have light sensing organs such as eyes, but they do however have neuronal connections that allow them to sense light. In other words they don’t see, they sense. C.ellegans tend to avoid light by fleeing from its origin; they are described as negative phototaxis.

What is the electronic sensor ?

The UV sensor we used for our experiment is the Adafruit VEML 6070 UV sensor. It detects the UV in a room and gives a values between 0 and 65 535 Arbitrary Unit. This means that there is no specific unit for the value that is given by this device. The VEML 6070 sensor is easy to use with an arduino (a little card that looks similar to an integrated circuit that memorizes and executes code).

About the biological setup

The biological setup comprised of a binocular magnifying glass pointing to a plate placed on top of a plastic box. Inside the plastic box was the LED that lit up the plate for 5 minutes.
The plates where divided in 3 zones : 2cm diameter, 6cm diameter and 9 cm diameter. After the 5 minutes exposure, we counted manually the number of worm in each zone and expressed that number as a global percentage. We made this experiment for 5 different UV intensities : 0, 100, 150, 200 and 255.

About the electronic sensor

The electronic sensor was connected to an Arduino. Here, we also tested 5 different intensities of UV, the same as the biological setup. The setup was very similar to the biological one : the LED was inside the plastic box, and light up the plate. We took 4 different measures (at different place on the plate) for each intensity.

The VEML 6070,

a sure value ?

After testing the UV sensor, we can assert that yes, UV sensor gives a good index of UV intensity. Our test shows a curve close to a famous function that is « The intensity of the light decreases with the distance of receptor.»

The graph against represents this law.

However, our experiment lacked measurements between 0 and 1 cm, so we don’t have enough data to fit the curve.

**What about the C.elegans ?**

So, did our little worms react as we expected? Not really. Indeed, the majority of worms stopped in zone 2 and didn’t go to zone 3, which was the farthest from the UV.

Another weird behavior of worms is that they were moving to zone 2 when the intensity of UV was 0… So we had to consider that worms were influenced by other factors....

After speaking with our tutor, we came with the following conclusions :

Worms are influenced by a gradient of temperature in the plate

Worms are influenced by the light of the binocular magnifying glass

Worms are influenced by other factors such as food in the medium or light of the day…

Worms are worms and don’t care about what is logical

So, who wins the title of best sensor ?

After carefully comparing our data, we can conclude that both C.elegans and UV sensor are sensitive to UV. However, there is a real difference in their precision and we can assert that the UV sensor is more reliable than C.elegans. So if there is one thing you need to take from this post, it’s that nothing beats a good old electronic UV sensor!