Hardware

Overview

The hardware team focuses on developing a low-cost, portable fluorescence detector inspired by the biological work from last year. We found greater value in creating a fluorescence-based system—rather than a color detector—because fluorescence offers higher sensitivity and is easier to implement for our application. While commercial fluorescence systems such as the BD FACSCanto™ II flow cytometer, Thermo Fisher QuantStudio™ PCR system, and Bio-Rad CFX96 Touch™ detector are widely used for research and clinical diagnostics, they are also complex and expensive, often costing tens of thousands of dollars. Our goal is to design a simplified, affordable alternative using LED excitation, photodiode sensing, and an ESP32 microcontroller to process and transmit data to a smartphone app. This approach enables an accessible, point-of-care diagnostic tool that brings reliable early cancer detection closer to patients while keeping costs far below those of commercial systems.

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Inspiration

Our design draws inspiration from Wu et al. (2012), Knowlton et al. (2017), Cho et al. (2019), and the iGEM Lambert GA 2022 Micro-Q device. Together, these works demonstrate that sensitive fluorescence and scatter detection can be achieved with low-cost LEDs or lasers, simple photodiodes/APDs, and modular 3D-printed housings, validated against commercial systems. This shows that affordable, portable, and reliable analytical tools are possible without relying on bulky or expensive components.

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Research Papers

The design of this device was heavily informed by several research studies that explored compact and cost-effective fluorescence detection systems. Each paper provided key insights into component selection, optical configuration, and performance optimization that guided our engineering decisions.

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Cho 2019

https://doi.org/10.3390/s19102301

Comparison between different components

Gas lasers:

• Short lifespan
• High cost
• “a trained professional is required to operate them”
• Affected by thermal effects → interfere with constant output

LEDs:

• long lifetime (5000–23,000 h)
• low cost (1–10 US dollars)
• “no requirement of trained professionals in its use”

Dichroic optical filters:

• high transmission rate
• narrow pass bands
• Expensive
• only a single wavelength at a time

How is the reliability of the device measured
“the fluorescence intensities were compared with the enumeration of the cells using hemocytometer to determine its performance accuracy and statistically analyzed by Student’s t-test. Moreover, quantified fluorescence intensities with excellent linear correlations were converted and applied to estimate the number of target cells by using a linear regression model.”

Their components:
470 nm LED (Photron, 3 W, Tokyo, Japan) output 1.4 W
Photodiode (FDS100, 350–1100 nm, Thorlabs, Newton, NJ, USA)
plano-convex lens (BK7, Plano-Convex Lens, Thorlabs, Newton, NJ, USA)
3D designed cuvette holder
Microcontroller (PIC16F877A, Microchip, Chandler, AZ, USA)
load resistors (100, 200, and 390 kΩ)

How to slower uncertainty:
“LED was warmed for 30 min before the test, and the temperature was controlled to be less than 25°C”
“through an excitation filter…passing through the emission filter” so two filters?
“the PD was also tuned for 30 min before the test to suppress the thermal effects.”

Smart designs:
Use of plano-convex lens to focus more light on the photodiode
Load resistors to optimize and amplify the photocurrents to read

Filter comparison (same LED):
With #74 (480 nm) excitation + 500 nm emission: slopes lower than “no ex. filter” case but still linear (e.g., SSC slopes 0.55/1.15/2.24 at 100/200/390 kΩ; R² ≈0.98–0.99)
With #369 (470 nm) excitation + 500 nm emission: SSC slopes 0.87/1.84/3.5 at 100/200/390 kΩ; R² ≈0.97–0.99.

Calibration:
Fitted relationship (for the “no excitation filter + 500 nm emission” condition):
Cell number = (0.005·x² + 0.047·x) × 10⁶, where x = fluorescence intensity (a.u.).

Cross-check vs. hemocytometer (n=10 per concentration): no significant difference (p > 0.05); both methods linear (R² ≥ 0.98).

Uncertainty:
30 min warm-up for LED and PD; temperature kept < 25 °C.
Black ABS 3D-printed holder to block stray light; precise filter/lens slots; plano-convex lens to focus onto PD.
Note: higher-gain resistors raised RSD slightly; can be improved with constant-current LED drive (they used one).

Cost:
Total parts ≈ $94 (LED, PD, lens, MCU, LCD, PSU, PCB, filter booklet, constant-current module). Well under typical cytometry gear.

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Knowlton 2017

https://doi.org/10.1039/C7LC00706J

Smartphone
Samsung Galaxy S6 selected → high-res camera (Sony IMX240, 1.34 µm pixels) and manual focus.
Choice balanced portability with enough optical resolution to capture cellular detail.

Optical
3D-printed chassis: modular case + optical block. Light, cheap, swappable; ~214 g (excl. phone).
Lens: single aspheric objective (Edmund Optics Ø6.33 mm, NA ~0.64) mounted 4 mm from phone camera. Minimal optics = easy alignment + low cost.

Illumination
LED modules: white, blue, UV → interchangeable depending on imaging mode (brightfield, fluorescence, darkfield).
Side-light geometry reduces glare.
Power: 2 × CR2032 coin cells + 220 Ω resistor; slide switch to cut idle drain. Field-friendly, <$3.

Filters
Used low-cost plastic emission filters (Roscolux #19, #389, #74) instead of expensive dichroics.
Relied on RGB channel separation in the phone to digitally isolate fluorescence.

Magnetic Levitation
N52 neodymium bar magnets (50.8 × 2 × 5 mm), arranged like-poles facing, to create a field gradient.
Microcapillary channel (borosilicate, VitroCom) placed between magnets.
Paramagnetic medium (gadobutrol or iodixanol) used for density-based focusing of cells.

Cost
Core device hardware: ~$105.87 (lens, magnets, LEDs, filters, PCB/printed parts, power).
Per-use disposables: $1 for capillary + diluted gadobutrol ($0.004 per assay).
Meets point-of-care requirement: cheap, portable, low-maintenance.

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Wu 2012

https://doi.org/10.1039/C1AN15867H

Excitation
High-power blue LED (3 W, CREE, 80–90 lm) chosen instead of lasers/arc lamps.
Advantages: cheap, mass-produced, long lifetime (>10,000 h), low power, compact.
Collimated using a 16 mm CCTV lens (cheaper than convex lens).
Band-pass filter (420–490 nm) removes overlap with fluorescein emission.

Optical
Epifluorescence configuration: LED light reflected by 505 nm dichroic, focused through microscope objective (20× or 40×).
Fluorescence collected by same objective → dichroic → long-pass filter (520 nm).
Additional focusing lens + 1.2 mm pinhole to suppress stray scatter.
Compact design (15 × 7 × 24 cm).

Objectives
20× objective (NA 0.40, WD 8.8 mm) → longer working distance, compatible with chips.
40× objective (NA 0.60, WD 3.0 mm) → tighter focus (~150 µm), 4× better S/N.

Photon Detector
Avalanche Photodiode (APD, AD500-8-TO52S2, Silicon Sensor, Germany).
Driven at ~121 V using low-cost HV supply (0–200 V, Dongwen).
Current converted via I–V converter (op-amp TL082CN, 10 MΩ resistor).
Much cheaper and smaller than PMT modules; compact enough for POC.

Electronics
USB-6211 DAQ card (National Instruments) → acquires APD signal, controls LED pulsing.
Data processing in LabVIEW (average smoothing, lock-in, or time-specific averaging).
Two LED modes tested:
DC mode + simple averaging → best S/N and peak shapes.
Square-wave pulsed mode → allows lock-in amplification, less heating.

Power
LED mounted in aluminum flashlight shell → acts as housing + heat sink.
System stabilized after ~20 min warm-up; <5% drift over hours.

Cost
Total system cost: ~£150, including optics, LED, APD, HV supply, and dark-box.
Filters were the most expensive component; smaller custom filters could further reduce cost.

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Design

Each component in our device was carefully selected to balance precision, efficiency, and simplicity. The OPA380 amplifier processes the tiny signals from the MTD5052W photodiode, ensuring stable, low-noise light detection. A 505 nm emission filter isolates the specific fluorescence signal emitted by our dye, while the 460–465 nm LED provides the exact excitation wavelength needed for accurate fluorescence measurements. The D1 Mini ESP32 microcontroller coordinates all operations, from reading the sensor data to displaying results on the OLED screen, which was chosen for its clarity, simplicity, and 3.3 V compatibility. Power is supplied by an 18650 lithium-ion battery system with built-in protection and charge monitoring, making the device safe and portable. Together, these components form a compact, reliable, and user-friendly fluorescence detection system designed for both research and practical field use.

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Amplifier

Why We Chose the OPA380 Amplifier for Our Project

For our project, we needed an amplifier that could reliably process very small signals from our photodiode and turn them into a clean, usable output. After evaluating different options, we chose the OPA380 Precision, High-Speed Transimpedance Amplifier because it offers the performance our device requires:

1. Optimized for Photodiodes The OPA380 is designed specifically for photodiode monitoring, making it ideal for converting tiny current outputs into accurate voltage signals.

2. High Sensitivity and Low Noise With a 50pA max input bias current and ultra-low noise, the OPA380 can detect even the smallest changes in light without distortion.

3. Wide Dynamic Range It measures currents from 1nA to 100µA in a single stage, ensuring accuracy across a wide range of light conditions.

4. Fast Response A 90MHz bandwidth and >1MHz transimpedance speed allow real-time detection and quick system response.

5. Stability and Precision The amplifier maintains accuracy with an offset voltage of 25µV and minimal drift (0.1µV/°C), ensuring reliable operation over time and varying temperatures.

6. Flexible Output It can output signals from 0V to nearly 5V, matching the input range of our microcontroller for easy integration.

Summary

The OPA380 provides the precision, speed, and stability our project needs to amplify photodiode signals accurately and efficiently.

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Emission Filter

Why We Chose a 505 nm Emission Filter for Our Project

Our project uses the fluorescent dye DFHBI-1T, which is excited at 460 nm and emits at 505 nm. To capture this signal accurately, we use a 505 nm narrowband emission filter. Here are its advantages:

1. Signal Specificity The filter only passes light at 505 nm, blocking background light and stray excitation at 460 nm. This ensures the detector measures only the intended fluorescence.

2. Improved Sensitivity By removing unwanted wavelengths, the filter increases the signal-to-noise ratio, allowing detection of even faint emissions.

3. Photodiode Compatibility Our photodiode (MTD5052W) has peak sensitivity near 525 nm. The 505 nm signal falls within this range, ensuring efficient detection.

4. Reduced Crosstalk The narrowband filter prevents interference from ambient or reflected light, avoiding false readings.

5. Robust Performance By blocking ambient light, the system remains reliable in both lab and real-world environments.

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LED

Why We Are Using a 460–465 nm LED in Our Project

For our fluorescence-based detection system, the LED is the light source that excites the fluorescent dye. The chosen LED emits in the 460–465 nm range, which matches the excitation peak of our dye (DFHBI-1T at 460 nm). This precise alignment ensures strong and efficient fluorescence.

Advantages

• Optimal Excitation
  The emission range directly overlaps with the dye’s excitation peak, maximizing absorption and signal strength.

• Adjustable Output
  Available in multiple power levels (1W, 3W, 5W, 10W), allowing us to tune the light intensity as needed.

• Efficient and Compact
  LEDs consume little power, generate minimal heat, and are ideal for portable, battery-powered devices.

• Stable and Durable
  LEDs provide consistent light output and long lifetimes, ensuring reliable measurements.

• Cost-Effective
  Widely available and inexpensive, making them practical for scalable devices.

• System Compatibility
  The blue excitation light works seamlessly with our 505 nm emission filter and green-sensitive photodiode, ensuring clean signal detection.

In summary: The 460–465 nm LED efficiently excites our dye, provides flexibility in brightness, and integrates well with our optical setup, making it essential for reliable fluorescence detection.

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Microcontroller

Why We Chose the D1 Mini ESP32 as Our Microcontroller

For our project, we needed a microcontroller — the “brain” that coordinates how everything works together. After comparing options, we chose the D1 Mini ESP32. Here’s why:

1. Built-in Wi-Fi and Bluetooth The ESP32 provides both Wi-Fi and Bluetooth, letting our device connect to the internet or directly to a phone without extra hardware.

2. Strong Processing Power Its dual-core processor runs much faster than older boards like the Arduino Uno. This allows it to handle multiple tasks — reading sensors, updating the screen, and managing connections — smoothly.

3. Energy Efficiency The ESP32 has ultra-low power modes (down to microamps), making it ideal for battery-powered devices.

4. Flexible Connections The ESP32 links easily with all parts of our system:

• Photodiode and Amplifier: Reads and processes light signals.
• Screen: Connects via I2C or SPI to display results.
• Buttons: Simple GPIO pins for start/stop control.
• LEDs: Drives indicators for status feedback.
• Power Supply: Works at 3.3V, compatible with most sensors and modules.

5. Secure and Reliable Built-in features like secure boot and data encryption protect the system against tampering, essential for connected devices.

6. Compact and Affordable Small, breadboard-friendly, and cost-effective, the D1 Mini ESP32 is perfect for both prototyping and final designs.

Why This Matters for Our Project

The D1 Mini ESP32 makes our device connected, efficient, and user-friendly. It ties together sensors, screen, controls, and wireless communication in a single reliable platform.

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Photodiode

Why We Chose the MTD5052W Photodiode for Our Project

Accurate light detection is essential for our project, and the MTD5052W photodiode is a strong fit. Here’s why:

Optimized Sensitivity

With peak sensitivity at 525 nm, the photodiode aligns closely with the emission wavelength of our fluorescent dye, DFHBI-1T (505 nm, excited at 460 nm). This ensures efficient signal detection.

High Reliability

Its hermetically sealed TO-18 package with a gold-plated flat top provides durability and protection from environmental factors, ensuring consistent performance.

Low Noise

The photodiode’s very low dark current (as little as 5 pA) minimizes false signals, which is crucial for detecting low light levels.

Wide Angular Response

A detection angle of ±55° makes the system more forgiving to slight misalignments between the light source and detector.

Fast Response

Switching times in the nanosecond range allow the photodiode to detect rapid changes in light intensity, ideal for real-time measurements.

Compact Active Area

Its 0.57 mm² active area helps focus detection on the intended light source, reducing interference from stray light.

Summary

The MTD5052W photodiode combines high sensitivity, low noise, and fast response in a robust package. Its spectral match with DFHBI-1T fluorescence makes it an excellent choice for precise and stable light detection in our project.

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Power Supply

Why We Chose This Battery System for Our Project

For our project, we needed a reliable way to power the device. Since it must be portable, safe, and easy to use, we chose a combination of three parts:

• EVE 18650 lithium-ion cell
• Battery shield
• Battery capacity indicator

Long-Lasting Power

The 18650 cell provides 3500 mAh of energy in a compact size, giving our device long operating time between charges.

Safe and Simple Charging

The battery shield allows safe recharging via a standard micro-USB cable and regulates voltage to 3.3V and 5V, matching our components.

Stable Power Management

The shield ensures steady power delivery, protecting sensitive electronics.

Clear Battery Monitoring

The capacity indicator shows the remaining charge, giving users a clear signal when recharging is needed.

Why This Matters for Our Project

This system combines endurance, safety, and ease of use. The 18650 cell supplies energy, the shield manages charging and regulation, and the indicator keeps users informed — together forming a practical and user-friendly power solution.

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Screen

Why We Need a Screen

Our project needs a screen to show numbers, messages, and results so users can easily understand what the ESP32 is doing. The screen can also display a QR or binding code for quick phone pairing.

First Try: LCD + Potentiometer

We began with a 1602A LCD screen that needed a potentiometer to adjust text contrast. While functional, it had drawbacks:

• Contrast had to be adjusted each time.
• Required many wires (up to 10).
• Needed extra level shifters since the ESP32 is 3.3V and the LCD 5V.

This setup worked but was too complex for beginners.

Improvement: OLED Screen

We switched to a modern OLED screen for a simpler, more capable solution:

• No contrast knob: always readable.
• Fewer wires: uses I²C or SPI (just 2–4 signal wires).
• 3.3V compatible: connects directly to the ESP32.
• Better visuals: supports text, graphics, and touch.
• Extra feature: can display a QR code for phone connection.

Connection

According to our wiring diagram, the OLED uses I²C:

VCC → 3.3V GND → GND SCL → GPIO22 SDA → GPIO21

This requires only four wires, far fewer than the LCD setup.

Why This Matters

• Simpler build with fewer parts.
• Cleaner wiring and no adjustments needed.
• Modern look with sharper visuals.
• Phone pairing via on-screen QR code.

Final Choice:
We replaced the LCD + potentiometer with an OLED. It’s easier, cleaner, beginner-friendly, and supports phone binding through QR codes.

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Fusion 360

The fusion parts are the structural components designed to securely hold and organize all the electrical elements within the final device enclosure. The final product will take the form of a compact and durable box, in which each sensor, display, and electronic module is precisely mounted using custom-designed 3D-printed fusion parts.

Each fusion part has been modeled in Fusion 360 to ensure accurate fitting, mechanical stability, and easy assembly. These parts include holders for the battery shell, battery indicator, D1 Mini ESP32 microcontroller, emission filter, and screw-threaded mounts for control buttons.

Each holder features mounting holes, grooves, or supports that align perfectly with the corresponding components, reducing internal vibration and preventing disconnections during operation.

Together, these fusion parts form an integrated mechanical framework that keeps all electrical parts neatly positioned inside the box. This modular design not only simplifies assembly and maintenance but also ensures that the internal wiring remains organized and protected.

Once fully assembled, the fusion parts collectively maintain the integrity and compactness of the system while allowing accessibility for testing, replacement, or future upgrades.

Drawings

Battery indicator holder drawing

Battery shell holder drawing

D1 mini holder drawing

Emission filter holder drawing

Screw thread for buttons drawing

Cookie cutter drawing

This was used to cut cookies for the bake sale.

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ISOs

We are following these ISO standards to ensure our device produces accurate, consistent, and scientifically reliable measurements, giving users and researchers confidence that the data collected by our system meets international quality and calibration standards.

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ISO_10012

ISO 10012 is an international standard that ensures all measuring devices and processes in a project are accurate, consistent, and reliable.

For our system — built with sensors, amplifiers, displays, and controllers — this means we can trust the data we collect and present.

By following ISO 10012, we reduce the risk of errors caused by faulty measurements, improve the overall quality of our results, and provide confidence to users, regulators, and partners that our device is producing valid information.

In short, it strengthens the credibility of our project by making sure that every reading, from light detection to battery monitoring, is both precise and dependable.

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ISO_24421

ISO 24421:2023 is an international standard that defines the minimum requirements for measuring optical signals in photometric methods used on biological samples.

These methods include bioluminescence, chemiluminescence, fluorescence, and absorption — all of which are widely used in biotechnology and life sciences.

By following ISO 24421, our project ensures that optical measurements are accurate, repeatable, and reproducible, which is critical for reliable analysis of biological data.

This standard also provides guidance on calibration, verification of instruments, and the use of optical references, thereby reducing measurement errors and increasing confidence in our results.

In short, ISO 24421 strengthens the scientific credibility of our system by guaranteeing trustworthy optical signal measurements.

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