Team:Calgary/Measurement Hardware
LUMOS
Overview
New biosensors are always being developed for a wide variety of applications, such as disease detection, quality control, forensics, and many more[1]. There are various types of biosensors, each with its own advantages and disadvantages. Bioluminescent biosensors, for one, measure light emitted from a biological specimen and translate the light signal into a readable output. Some biosensors of this kind can be expensive and complicated to use. Thus, we introduce Lumos, a low-cost and modular luminometer. We designed Lumos with cost and ease of use in mind. he device is composed of modular components for easy replacement and to allow for future hardware developments, like installing a fluorometer module.
A typical biosensor can be divided into five components[1]: analyte, bioreceptor, transducer, electronics, and display. The analyte is a substance of interest that needs detection. The bioreceptor is what recognizes the analyte. The transducer is one of the most important components, as it converts one form of energy into another (typically electrical signal). This signal is then transferred to the electronic component of the sensor for interpretation, and the resulting data is shown on an external display. Optical biosensors work this way by converting light into an electric signal through a process called luminometry.
In simple terms, luminometry is the process of measuring light[2]. This is usually done by quantifying the incident photons on a photosensitive surface. Photoresistors, photodiodes, and phototransistors are examples of transducers that can convert light into electrical signals. Luminometry differs from fluorometry in that it does not need an excitation source to induce glow in the analyte, which reduces the complexity in hardware design.
DETAILS
Lumos was made with cost-effectiveness and ease of use in mind. Therefore, the sensor was designed using affordable materials. Outlined below are the components used for Lumos.
Circuit
The LCD1602 screen serves as the default external display for Lumos. It is equipped with an I2C driver to reduce the amount of pins used on the microcontroller. The ESP32 microcontroller unit[3] is the sensor’s main electronic component. It is a low-power, system on a chip microcontroller with built in Bluetooth and Wi-Fi capabilities. The TSL237 sensor[4] is the most important part of the device, as it converts the light energy into computer-readable electrical signals. This particular sensor is a light-to-frequency photodiode. It converts incident light into a 50% duty cycle square wave, with frequency directly proportional to the light intensity. The circuit diagram for Lumos is shown below.
Figure 1. Simplified schematic diagram for the Lumos biosensor.
Software
The ESP32 microcontroller unit can be programmed using many different types of IDEs, including Arduino IDE[5], which is written in C++. A complementary mobile phone application was also developed to take advantage of ESP32’s Bluetooth Low Energy functionality. The application was made with Thunkable[6] to make the Bluetooth Low Energy setup easier.
Materials
Below is a list of materials needed to build the biosensor, along with their estimated prices.
Figure 2. Materials table for the biosensor.
ENGINEERING DESIGN CYCLE
The key to innovation and progress in any area is to go through multiple iterations of the engineering design cycle. We put into consideration the iGEM engineering cycle (Design, Build, Test, Learn) while working on the biosensor. All the circuits built were tested using an LED bulb to simulate the glow produced by the analyte.
Iteration 1
For our first iteration of the design cycle, we based our design off of previous iGEM fluorometer designs, specifically the ones made by iGEM Cambridge 2010[7] and iGEM Aachen 2014[8]. The circuit was coupled with an operational amplifier to amplify the input voltage from the photodiode. The photodiode used was an IR-blocking photodiode which was sensitive to visible light. After building the circuit and testing its performance, we noticed that it was not giving us the results we wanted at higher light intensities. Several variations of the circuit were also tested, but none of them were effective enough at detecting the light given off by our LED.
Iteration 2
After learning that our sensor was not sensitive enough to the changes in light intensity, we decided to design another circuit using a TSL237 light-to-frequency sensor. We tested the system using an Arduino microcontroller to make the debugging process easier in case we needed to find the root cause of our issues with the circuit. The digital photodiode proved to be a better sensor in terms of sensitivity to small changes in the light output, so we decided to keep this design in future iterations of the cycle.
Iteration 3
After verifying that the TSL237 works, we included an external visual display in the circuit design. Adding the LCD1602 screen to the circuit enabled us to read the frequency readings outside of the serial monitor. Several debugging sessions were performed as some parts were defective and were not working as expected, which meant we had to purchase newer parts.
Iteration 4
After we made sure that everything worked as expected on the Arduino, we switched to ESP32 to take advantage of its Bluetooth Low Energy (BLE) functionality. This iteration involved more of the software design process, which means more debugging and code iterations were done to make the program work. Adding in BLE functionality meant we had to design both the server side and the client side. The server side was programmed primarily with the Arduino IDE using C++. The client side was programmed using Thunkable, a software designed to make Android application development easier. At the end of this iteration, we were able to figure out how to transmit data from the client (mobile phone) to the server (ESP32) by using Thunkable’s BLE function block.
Modularity
One of our main goals at Neocycle is to reduce the amount of electronic wastes that do not get reused. By putting the principle of modularity at the core of the design process with Lumos, we are reducing the amount of waste produced when upgrading hardware parts. Not only is it easier to upgrade the parts from a developer standpoint, it is also easier for users to discard old parts without throwing out the entire device.
RESULTS
After combining all the 3D-printed parts, this is what the final product looks like. Several revisions to the product will be performed shortly, such as the addition of a calibration function for the biosensor, and the soldering and integration of the circuit into the chassis.
Figure 3. Physical prototype for the luminometer.
NEXT STEPS
Better UI
The user interface is an essential aspect to consider in every software program, as it determines the usability of a program from a user’s perspective. The quality of UI can sometimes make or break a product. With this in mind, some Lumos users may not have an Android phone to use for data transmission. Hence, it is important that we develop a better manual mode, which does not involve the use of any external device. In future iterations of the product, we will be adding more buttons, and a bigger screen to allow better user experience.
Additional Module
Some analytes do not produce light via chemiluminescence. Some of them need an excitation source to fluoresce. Therefore, we also need to design a new module that includes an excitation source and an excitation filter for fluorescent analytes.
New Sensors
TSL237 is an obsolete component, and it can be hard to find sources online nowadays. It is important that every electronic component can be purchased with ease. There are a few alternatives for TSL237 online, and we plan to test their performance in the future.
CAD Redesign
As it currently stands, the Lumos chassis looks blocky and bulky. It also has a lot of wasted space inside, as the components are not fully compact. The goal in future iterations is to design a more compact product and minimize the wasted space, in order to save on 3D filament and money. By optimizing the chassis design, we also aim to reduce the waste on plastics, thereby helping the environment.
REFERENCES
Bhalla N, Jolly P, Formisano N, Estrela P. Introduction to biosensors. Essays in biochemistry. 2016;60(1):1–8.
Vitl Life Science Solutions. Vitlproducts.com. [accessed 2021 Oct 16]. https://vitlproducts.com/blog/what-is-luminometry
ESP32. Espressif.com. [accessed 2021 Oct 16]. https://www.espressif.com/en/products/socs/esp32
Digikey.ca. [accessed 2021 Oct 16]. https://www.digikey.ca/catalog/en/partgroup/tsl237/29745
Software. Arduino.cc. [accessed 2021 Oct 16]. https://www.arduino.cc/en/software
Thunkable: Build powerful, native mobile apps without coding. Thunkable.com. [accessed 2021 Oct 20]. https://thunkable.com/#/
Team:Cambridge/Tools/Eglometer - 2010.igem.org. Igem.org. [accessed 2021 Oct 20]. https://2010.igem.org/Team:Cambridge/Tools/Eglometer
Team:Aachen/OD/F device - 2014.igem.org. Igem.org. [accessed 2021 Oct 20]. https://2014.igem.org/Team:Aachen/OD/F_device
