Olfactometer
Our new olfactometer has been designed for three odors, and has space to accommodate up to six odors.
The background
Numerous changes were made to the 2023 olfactometer prototype to refine the design to suit the needs of the project. Firstly, the new olfactometer was designed to support up to six odors in a symmetrical scaffold, with a hollow interior to allow space for the circuitry and piping to neatly fit into and to be hidden beneath the roof. We chose to enclose all the element, including the pipes, inside the box to contain noise and ensure stability of the setup.
Olfactometer top view to accommodate six odor vials and all valves and wire connections.
The roof of the box slots into the base box which is designed with a thumb indent to assist the experimenter to remove the roof when necessary. The roof supports up to 16 valves in designated positions and additional holes are cut out alongside each valve to allow for cable tie fixing of the valves to the box - this is to ensure a stable and robust final system.
We've decided to change our system by incorporating five additional valves, providing us with finer control over odor release. In the schematic, SA represents a solenoid valve responsible for introducing air into the system, while SB facilitates airflow through the main tube for system purging. SC and SD (with a symmetric counterpart) play a role in directing air through one side of the box into the odor tubes. Introducing S1 and S2 valves, we regulate the flow of air and odor. S1 allows air into the odor 1 tube, while S2 enables the release of air infused with odor into the main olfactometer tube. This setup is the same for S3 and S4 for odor 2, as well as S5 and S6 for odor 3. Symmetry is maintained on the other side of the box. Unlike the previous design, which had non-return valves, we used additional solenoid valves. This strategic shift allows for control using the Arduino and ensures prevention of odor leakage into both the system and the surrounding environment.
The olfactometer box
Below, we demonstrate the 3D-printable draft of the olfactometer box designed using Fusion 360. In this design, grooves represent the placement of the solenoid valves. The design was later realised without grooves using a plastic sheet due to 3D-printer material constraints.
The odor port
As one of the main tasks in our project, we worked on designing a cone to be attached at the end of the air output tube, that will allow for a precise odor delivery to the mouse, yet hold space for other features of the system such as the water spout of the licking tracking and water delivery part. We created three drafts by cutting of cone shaped plastic bottoms off of Flacon tubes or a plastic packaging for a pipette filter. Our final model that has been added to the olfactometer is the bottom of a Flacon tube. We cut it off using a paper cutter knife, drilled a hole in the diameter of the tubes into the tip and sanding down the cutting edges. Finally, we attached the odor port to the end of the air output tube using super glue.
Three odor port designs: (left) prototype made from Falcon tube (middle) final odor port design attached to the tube (right) prototype made from plastic packaging for a pipette filter
The solenoid valves
If you want to know more about solenoid valves, you can find here a video that explains how they work:
The assembly
To ensure the synchronisation of the entire system, the different components have been designed with special interest into how they can connect together to create a cohesive system.
The idea is to design a single assembly of all these components to image the olfactory bulb of mice during exposure to different odors. Alongside this, the licking behaviour of mice is tracked as a physical reference to gauge the mouse emotion, where licking signifies a level of comfort.
Graphical representation of final olfactometer system assembly
1. Building the Olfactometer box
To construct the box, we opted for plastic board as our material of choice. While ideally, we would have utilised a laser cutter for precision, though it wasn't accessible to us at the time. Instead, we meticulously cut the pieces using a paper cutter, ensuring accuracy to the best of our abilities. The pieces were then seamlessly joined together using super glue. Additionally, we drilled holes to accommodate various components such as the tubing, Arduino ports, power supplies, and water supply tubes, ensuring a neat and organised assembly process.
2. Building the vials box
Additionally, we built vial boxes for both sides of the olfactometer using the same material as the main box. Despite the absence of a laser cutter, we used traditional tools to cut and assemble the boxes with precision. This allowed us to create functional and cohesive components that seamlessly integrate with the olfactometer.
3.Tubing and valve attaching
We carefully positioned the components according to the pre-designed layout, as visible in the background of the olfactometer. Securing the valves with cable ties ensured stability, while gluing the tubes to the valves provided assurance against any potential leaks. This year, we opted for more flexible tubing to enhance the efficiency of odor transportation, a strategic choice aimed at optimising performance.
4.Placing of Arduino, Soldering Board and Transistors
We crafted small boxes for the Arduino and soldering board using the same material as the main box, ensuring precise alignment within the designated space. Additionally, recognising the need for enhanced stability, we introduced an additional wall within the olfactometer to accommodate the transistors. This modification, implemented mid-production, improving the design for optimal performance. Each transistor was securely fastened to the wall using cable ties, through drilled holes facilitating their integration.
5.Wiring the system
After positioning all components, we connected the Arduino, solenoid valves, soldering board, and transistors with wires, as depicted in the control section with graphical abstracts and videos. We organised the wires into groups based on their intended connections. This phase demanded considerable time and effort to grasp and execute effectively. Should you encounter any confusion or have inquiries, please don't hesitate to reach out to us. We're here to assist you.
Video of final olfactometer assembly