Senior Design Team sdmay25-17 • MicroBial-Electronic Pill Sensor SD Site

Project Overview

Excessive nitrate concentration in bodies of water, often a result of agricultural runoff, poses significant environmental hazards, endangering both aquatic life and the lives of those consuming the water. Current methodologies for identifying nitrate concentration in agricultural runoff are intensive, expensive, and inefficient, often requiring manual sampling and off-site analysis. By providing more efficient, cost-effective, and autonomous nitrate detection, the microbial pill sensor aims to provide continuous monitoring of nitrate concentrations for both environmentalists and farmers. Improved access to environmental conditions allows users to make more informed decisions regarding the health of waterbodies and fertilization processes.

The microbial pill sensor uses a novel biosensing detection mechanism, relying on bioengineered microbes to identify the presence of nitrate in the environment. The microbes used by the microbial pill sensor have been genetically engineered to express green-fluorescent protein (GFP) due to the presence of nitrate. The concentration of nitrate in the environment can be determined through the fluorescent response of the expressed GFP, which is initiated, measured, and transmitted via the electronic components of the microbial pill sensor.

The microbial pill sensor is a cylindrical capsule with a radius of 15mm and a height of 47mm, broken into distinct modules. The bioengineered microbes are contained within a housing chamber, and the solution will flow in through a selective membrane located at the top of the capsule. The optical detection PCB and the microcontroller PCB are situated directly below the housing. A 488 nm wavelength LED is required to excite the expressed GFP, resulting in the emission of 532 nm wavelength light. The emitted light is captured by a photodetector, resulting in a photocurrent proportional to the presence of nitrate in the environment. A microcontroller is responsible for the activation of the LED at the desired interval and the transmission of the photocurrent value to an external device via low-power Bluetooth. An external GUI application processes the measurement and displays recorded nitrate concentrations for evaluation by the user.

The microbial pill sensor implementation currently consists of a functional photodetection PCB encompassed in the housing, along with optical emission and excitation filters, which is connected to an exterior ESP32-C3-Dev-Kit to enable MCU functionality. Complications in the design of the MCU PCB make the current MCU PCB design nonfunctional. The photodetection system is capable of a 52.02 mV / mW sensitivity with a ~100 μW limit of detection within the housing for 500 nm light. Poor selection of the excitation LED prohibits the device from properly exciting the necessary fluorescent response from GFP-expressing microbes. Bluetooth low-energy and Serial transmission of photogenerated voltage values have been demonstrated, with an external GUI application capable of receiving, displaying and saving the measured values to a CSV file for analysis by the user.

Future development of the microbial pill sensor will require proper development of the MCU PCB. Updates to the housing design will enable detection of fluorescent response by increasing the light intensity reaching the photodetection PCB through the implementation of lensing. Functional environment testing is required to characterize the lifetime, power consumption, transmission range, and environmental impact of the device.

Weekly Reports

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Status Reports

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Lightning Talks

Lightning Talk 1: Product Research
Lightning Talk 2: Problem and Users
Lightning Talk 3: User Needs and Requirements
Lightning Talk 4: Project Planning
Lightning Talk 5: Detailed Design
Lightning Talk 6: Design Check-In
Lightning Talk 7: Prototyping
Lightning Talk 8: Ethics and Professional Responsibility

Poster and Presentation

Poster Display
IRP Presentation

Design Documents

491 Final Design Document
492 Final Design Document