A New Method for Measuring Fluid Levels in Cell Culture Plates

Cell culture plates are widely used in laboratories to grow cells for various experiments. One important aspect of working with these plates is knowing the fluid levels within each well. Accurate measurements help scientists manage experiments better and avoid errors. In this article, we will discuss a method that uses computer vision and a simple setup to measure fluid levels in these culture plates without direct contact.

#The Need for Accurate Fluid Level Measurement

Cell culture procedures can be complicated and require precise handling of fluids. Automated systems are often used to improve the speed and consistency of experiments. It's crucial for these systems to deliver exact amounts of fluid. However, detecting fluid levels accurately is usually a challenge, especially in systems that do not provide feedback about the fluid volume present.

Traditional methods for measuring fluid levels often involve probes that come into contact with the liquid. While effective, these methods can lead to contamination, which may compromise the cell culture experiments. Non-contact methods, which measure fluid levels without touching the liquid, are much preferred, especially in sensitive applications.

#Optical Methods for Fluid Level Measurement

One way to measure fluid levels without direct contact is through optical methods. These approaches focus on how liquids interact with light. Different optical techniques exist for measuring fluid levels, and many rely on using Cameras and Light Sources to capture images of the fluid surface.

Some methods use well-placed sensors and lights at specific angles to detect changes in light caused by the fluid. However, these setups can become complicated when trying to pack multiple sensors tightly together in a culture plate. Another method involves using printed grids to visualize how light bends due to fluid levels, but it can be affected by the plate’s contents or ambient light conditions.

#A New Method for Measuring Fluid Levels

We propose a new method that combines a simple camera sensor with a bright light to detect fluid levels in culture plates. This method makes it easier to measure fluid levels accurately without being impacted by solid materials in the well. When the fluid fills a well, it changes the apparent size of the light source’s reflection. The size of this reflection can be analyzed to determine the fluid level.

To implement this method, we designed a 3D printed device that holds a camera and a light source above a 24-well culture plate. This setup allows for easy measurements across multiple wells in a single experiment.

#How the Method Works

The core idea behind this method is that as the fluid level changes, the way light behaves also changes. When light passes through the fluid, it bends, or refracts, depending on the fluid's properties. This bending creates an effect on how we perceive the light source. As the fluid level rises, the light source appears closer to the observer.

To create a simple understanding of this relationship, we can use basic principles of light refraction. As the fluid depth changes, the apparent distance of the light source also changes. By observing this change, we can derive a mathematical relationship that tells us the fluid level based on how the light source's apparent size changes.

#Setting Up the Measurement Device

We constructed a rig that can hold a camera and an LED light above the culture plate. The light shines down into the wells while the camera captures images of the resulting reflections. By using free software tools like OpenCV, the captured images can be analyzed to measure the size of the light reflection.

The setup is designed to work with a Raspberry Pi, a small computer that can process the images and run the necessary analysis. This means that the entire system can be made compact and inexpensive, making it suitable for various lab settings.

#Analyzing the Data

After capturing the images, the software measures the size of the light spot in the images. The program identifies the center of the light reflection and fits an ellipse around it, allowing for precise size measurements. This analysis can occur in real-time or on recorded images, making it flexible for different situations.

To ensure accuracy, we filter the measurements by looking at the stability of the readings. This helps prevent fluctuations caused by disturbances in the fluid, such as when new fluid is added or if the plate is moved.

#Results and Observations

The new fluid level measurement method shows promising results. As expected, there are specific ranges where the relationship between the size of the light spot and the fluid level remains linear. This means that, within these ranges, the system can provide reliable fluid level readings.

Initial tests revealed that when a well is dry, droplets of fluid can form rather than creating a stable layer. Once a small amount of fluid is introduced, the measurement system becomes operational. Interestingly, moistening the well beforehand can improve measurement accuracy with lower fluid volumes.

#Advantages of the New Method

The optical method presented has several advantages. First, it allows for non-contact measurement, reducing the risk of contamination. Additionally, the setup is cost-effective, relying on inexpensive camera hardware and software. This makes it accessible for many labs and encourages further development and use of similar techniques.

Furthermore, this method can be used in various applications beyond cell culture plates, such as larger storage containers and even with different types of fluids by adjusting the light frequencies used.

#Conclusion

In summary, measuring fluid levels in cell culture plates is essential for successful experiments. The new optical method discussed here provides a simple, effective, and accurate way to achieve this without direct contact with the fluids. This innovation could enhance automated systems in laboratories and open the door to new applications across different fields. As technology continues to advance, the use of low-cost optical measurements will likely become more common, leading to better practices in scientific research and experimentation.