Seoul-Korea developed Monitro to overcome the shortcomings of conventional nitrate sensors in terms of hardware durability, procedural inconveniences, and accessibility. It is a single system that incorporates both measurement and analytical functions. Monitro measures the nitrate concentration in a unit of µM within four to six hours by using an RGB color sensor connected to the Arduino circuit board with E.coli indicators encapsulated in alginate beads. Users can easily insert alginate beads into the sensor and obtain data on their mobile devices. Through Wi-Fi transmission, the Arduino chips can deliver data wirelessly to our software and provide accurate information about nitrate concentration.
Fig.1. Hardware(Monitro)
We underwent multiple designs and trials to materialize our unprecedented approach to dissolved ion sensors. As many ideas were put to the test, many were also removed. For example, many initial features, such as laser systems to light up the beads, were replaced with RGB sensors with integrated lighting systems and UV light for precision. Ultimately, our designs were perfected using CAD (Computer Aided Design) programs for accurate measurements and 3D printing.
Fig.2. A schematic of Monitro
Fig.3. A 3D model of Monitro
The Monitro sensor consists of two components: the base and the tower. The hole in the cuboid base (84 x 55 x 40mm) contains the alginate beads in transparent plates. The alginate beads are then translated by the color sensors in the tower and transferred into data. Underneath the alginate beads is an UV LED light (DC3.2v~3.4V, 365nm), which illuminates the beads for a clearer rendition of colors. The sole component that requires replacement for a new measurement is the alginate beads, without having to risk damage to the circuit boards and the main system.
Fig.4. RGB color sensor (left) and Biosensor bead(right)
Fig.5. Fluorescence observation of E. Coli beads using UV lights
The tower [41mm x 50mm] comprises the TCS34725 RGB sensor and UV lighting in the compartment between the lid and the main cylinder. The RGB sensor, connected to the Arduino Uno board, measures the RGB of the alginate beads with minimal infrared spectral components alongside its 30mm elevation from the plate for accurate measurements. In addition, the LED integrated into the RGB sensor illuminates the alginate beads to reflect light in the enclosed base with the UV light under the beads, providing necessary lighting under isolation from unwanted influences outside the sensor.
To retrieve information from the RGB sensor and transmit it to mobile devices, we used the Arduino Uno board to connect to client devices (mobile devices). However, this circuit board is interchangeable with models such as the ESP32 chip, a smaller computer chip that provides both Wi-Fi and Bluetooth connection.
Fig.6. ESP32 (left) and Arduino Uno (right)
Using 3D printers to test our prototypes, our team was able to develop suitable hardware for Monitro. While creating a simple, sustainable design that facilitates management and accessibility for the users, our incorporation of synthetic E.Coli beads maintains accuracy in units of µM; the design manages to address the previous problems with dissolved ion sensors. Most importantly, we have obtained the most significant factor as an “accessible” solution to the current sensor market at an estimated $75 per system. In the future, our team aims to develop other chemical measuring sensors by expanding on the alginate beads. Applying the construction used for Monitro to a wide variety of ions, our sensors would serve as viable solutions to the monitoring industry and further environmental issues.
