If our concept undergoes further development, it has the potential to offer an inexpensive, readily manufacturable, and modular sensor for detecting biofilm infections on medical implants. This innovation could significantly enhance the field of medical implant monitoring and infetion control.

We were able to design, construct, and test a biosensor that is cheap, easy to make, modular, and able to detect fluorescent proteins. Future iGEM teams can use the design, material list, and instructions to easily build their own biosensor. Additionally, each component of the system can be swapped out and adjusted (e.g. different sensing component or a different resistor). The Arduino code can also be adapted to suit the specific needs of the team. The biosensor can be made as simple or as complex as required.

In order to have a functional detection system, we decided to design a concept setup using two different fluorescent proteins in our design. The red fluorescent protein (mCherry) is used as a control, to make sure the sensor cells are still alive. Thus, the red fluorescent protein is constantly expressed. The green fluorescent protein (GFP) is only expressed when the biofilm is present.

The device should be able to excite the proteins to trigger fluorescence and then detect the fluorescent signal. The device we build, however, only focuses on detection. The light emitted by the fluorescent proteins travels through optic fiber cables. Here it reaches a photomultiplier tube which amplifies the signal since the light from the proteins itself is too weak. The signal is then converted into voltage using a transimpedance amplifier and is read by the Arduino board. However, we decided to proceed with a simpler design, described and used in hte sections below.

Figure 2: From genetic design to electronic sensing; Light Source → Optical Fiber → PMT → Transimpedance Amplifier → Arduino. The image on the left was made with BioRender.com. The image on the right was made with Tinkercad.com.

In the following sections we offer a more in-depth explanation of the parts:

Light Emission:
We are using two proteins, namely Green Fluorescent Protein (GFP) and mCherry. These proteins emit light when light is shined on them. The wavelength for excitation is 397 nm for GFP and 587 nm for mCherry.

Light Collection:
We need to collect the light we are interested in. This is done using an optical fiber cable. The fiber cable should be selected to be sensitive to the emission wavelength of GFP (506 nm) and mCherry (610 nm). It would be practical if the light emission and light collection could be accomplished using the same optic fiber cable.

Light Detection:
If the light intensity from the proteins is very low, a photomultiplier tube (PMT) is needed. The light gathered by the fiber optic cable is then channeled directly into the photomultiplier tube (PMT). The PMT uses the photoelectric effect to convert light into an electrical signal and is capable of detecting low levels of light such as single photons.

Signal Conversion:
The PMT outputs a current proportional to the light intensity it receives. This current needs to be converted into a voltage signal that an Arduino can read. This is typically done using a transimpedance amplifier, which converts the current output from the PMT into a voltage.

Signal Processing:
The voltage signal from the transimpedance amplifier can then be read by an Arduino. The Arduino can be programmed to process this signal in a variety of ways. As none of us had prior experience with designing and building electronics, we organized a brief meeting with ing. Therèse oelman, the electrical assistant at the University of Groningen. The meeting proved to be very insightful as Therèse recommended that we explore the idea of developing simulations utilising an LED light source. Additionally, she helped us with choosing materials for our setup and ordering them through the University of Groningen. We also borrowed materials needed for our setup from her. Her assistance was greatly appreciated. We have first built a setup with light emitted from green and red LEDs that simulate the GFP and mCherry. The second setup consisted of GFP produced in our lab which we excited with light of a specific wavelength prior to the measurements.

The components we used for our project are;

• LED Cyan Through Hole T1 345mm 30 mA (Green LED light that simulates with Green Fluorescent Protein) Farnell (αGFP). The emitted wavelength for αGFP is 506nm for αGFP.
• LED Orange T1 34 2500MCD 610NM (Red LED light that simulates mCherry) Farnell mCherry. The emitted wavelength for mCherry is 610nm Coin Cell batteries
• Tape
• Fiber Optic Cable Bare Polymer Plastic diameter 3 mm OMPF3000 Farnell
• NPN Phototransistor 570nm (TEPT5600), peak sensitivity 570 nm
• SBC Arduino UNO WiFi Rev2 PCE 45,68 ATmega4809 8bit
• Resistor (220Ω)
• USB cable
• Jumper Wire kit
• Breadboard
• Tape
• Dark Enclosure

Inside the Enclosure:
The LEDs emit light which the fibre optic cable collects and transmits to the phototransistor outside the enclosure.

Outside the Enclosure + Arduino Processing:
The phototransistor receives light through the fibre optic cable. As light intensity changes, the phototransistor’s behaviour causes a change in the current flowing through it. This change in current leads to a change in voltage at the phototransistor’s output. By monitoring this change in voltage using the Arduino’s ADC (via pin A0), we can detect variations in light intensity and infer the state of the LEDs (whether they are emitting light or not).

Figure 3: The suggested whole setup for the initial prototype.

Figure 4: The full prototype we tested in the previous steps connected to our app via Wifi, therefore the results are visible in an app on your phone.