Cell to Machine Communication

To create a means of communication from cell to machine, we chose the red fluorescence protein KillerRed as a reporter protein. The first condition that our device needs to fulfill is to record light intensity. Then it needs to generate fluorescence thank to a light source and a couple of excitation and emission filters. Firstly we will explain the choice of the different components, then the several experiences we did to find the most accurate parameters for each part of the device – the photodiode, Arduino and the optic.

The components

To record light intensity, we were inspired by the E. glometer of the Cambridge team of iGEM 2010.

The E. glometer of Cambrige team (iGEM 2010)
Device built by Cambrige team in 2010 to measure the light intensity of their LuxBrick
Source:https://2010.igem.org/Team:Cambridge/Tools/Eglometer

We use quite the same photodiode (TSL230RD) – same as the TSL230RP-LF but in surface mounted device (SMD) – and an Arduino Uno. Arduino is a single-board microcontroller created to make electronics more accessible. The main asset of the photodiode is that the output can be either a pulse train or a square wave (50% duty cycle) with frequency directly proportional to light intensity. Since we are using a microcontroller, it is easy to calculate a frequency with the digital input of the microchip thanks to high or low level and we will have a better resolution because low frequencies are easier to measure than low voltages. For the optic part we use a domestic LED lamp and a cube filter from a microscope with excitation and emission filters and an adjustable lens. A domestic LED lamp was chosen to allow us not to buy several high-power LEDS and built a card with a heat sink. This lamp illuminate with 520 lumens in a cone of 40° under 12V and 6W. The low voltage was chosen as a safety condition and the small angle to avoid losing to much light. The excitation filter is a green interferential filter to excite the red fluorescent protein and the emission filter is only a colored filter to have all the red light in order to have a more efficient measure. In the cube there is also a dichroic mirror that reflects all the green light and transmits all the red light. This mirror enables us to separate completely the photodiode from the light source.

The photodiode

Arduino

The optic

TALK'E coli: C2M part
on the left: the real device, on the right: functional schematic
The light from the LED lamp goes through the green excitation filter and illuminate the sample thanks to a dichroic mirror. Then the red fluorescent protein is now excited and re-emits red light that goes through a lens that concentrate it on the photodiode.