Hardware

Hardware: Portable Phosphorous Detection Device

Phosphorus is one of the key indicators of eutrophication levels in natural waters, where it exists mainly as dissolved phosphorus. Various analytical protocols exist to provide an offsite analysis, and a point-of-site analysis is required. The current standard method recommended by the Environmental Protection Agency (EPA) for the detection of total phosphorus is colorimetric, in which all forms of phosphorus are converted into orthophosphates via sample digestion (heating and acidifying) [1]. Several devices have sought to implement photoelectron colorimetric detection to provide remote analysis of these color-based changes. Whereas others have sought to develop electrochemical quantifications of phosphorous [1]. We follow a lab-on-chip approach [2] to capture the luminescence of our bacteria in relation to phosphorus levels.

Design

To determine if photoelectric detection was feasible, we augmented a PhenoPlate 96-well microplate with a 3D printed photodiode mounting unit (figure 1).

Our design utilizes a Centronic, OSD15-E Visible Light Si Photodiode to capture all emitted light given off during the bacteria-phosphate reaction. By printing such a design, reliable, accurate, and consisting testing can be attained through an augmented set up. Typical values are recorded via a luminescence plate reader which isolates a sample in complete darkness to capture photons through an in-built luminometer. Our design instead isolates a single sample instead of the entire plate. By fabrication our 3D design using resin printing, a mounting unit could be designed to 0.01 mm to completely isolate the bioluminescent photons. To capture the luminescence of the bacteria, a voltage amplification circuit was designed to increase the photodiodes sensitivity to photons (figure 3). If too much light was captured (e.g., through the flooding of ambient light between samples) the circuit would saturate, giving a readable range between 0-5V.

Testing

Testing was conducted with an array of cell concentrations to successfully capture and identify levels of luminance. For example, a cell concentration of OD600 = 1.3 yielded a voltage value of 60 mV (compared to 0v across a control) equating to a phosphors level of 0.01 mM.

Future Work

Next steps would involve the integration of a microcontroller within an encapsulated unit to provide a portable measurement solution. We envision refillable capsules as the most optimum form of measurements. Samples can be loaded within the transparent capsules and interested into the device, reducing contamination within the unit (like most microfluidic units).

We also aim to utilize the microcontroller to empower the user and community to save, record, and communicate their findings. This can be translated through an app which connects via Bluetooth to give users cloud-based and social sharing services. Possible features include:

  • Phosphorous “diaries”
  • Educational tools
  • Location-based sharing of captured levels
  • Reminders
  • Predictive models

Conclusion

Through our bioluminescent bacteria, we are able to detect phosphorous levels using photoelectric detection. This method is much cheaper than conventional devices and can be fully portable and scalable. Future work needs to provide more practical implementation and field testing alongside human-centered design to ensure the device and application meets intended user needs.

References

  1. A. V. Kolliopoulos, D. K. Kampouris, and C. E. Banks, “Rapid and Portable Electrochemical Quantification of Phosphorus,” Anal. Chem., vol. 87, no. 8, pp. 4269–4274, Apr. 2015, doi: 10.1021/ac504602a.
  2. “Frontiers | A Lab-On-Chip Phosphate Analyzer for Long-term In Situ Monitoring at Fixed Observatories: Optimization and Performance Evaluation in Estuarine and Oligotrophic Coastal Waters.” https://www.frontiersin.org/articles/10.3389/fmars.2017.00255/full (accessed Oct. 01, 2022).