Project showcase
A portable diagnostic that brings molecular testing to clinics without a lab, for about $57 in parts. I lead the team and own the electromechanical side end to end.
Closed-loop heating
What
The heater and its closed-loop controller, holding the NAAT reaction at 65°C within ±0.5°C on an ESP32.
Why
Isothermal amplification replaces the bulky thermal cycling of PCR, but it only works if the sample stays right at 65°C.
How
- Wrote a PID loop on the ESP32 that reads a thermistor at the heater and drives it by PWM
- Lifted the 3.3V rail to 5V for the heater with a boost converter, switched low-side by a MOSFET at 1 to 2 kHz
- Added a soldered thermal fuse that cuts power on runaway
- Put the heating plate in direct contact with the microfluidic chip through thermal grease
- ESP32
- PID control
- Thermistor
- PWM
- Boost converter
- MOSFET
- Thermal fuse
Inside the NAAT module
A control board, a sensing board, the microfluidic chip and a heating plate. NAAT amplifies genetic material at a constant 65°C, so it needs no PCR hardware.
An ESP32 runs the heater loop and the optics. USB-C and a solar cell charge a 5000 mAh LiPo; a 2.4" display and buttons run the test.
A boost converter lifts the 3.3V rail to 5V for the heater, switched low-side by a MOSFET under PWM. A soldered thermal fuse cuts power on runaway.
Underneath, each channel pairs a blue LED with a Vishay TEMD6200 photodiode, both facing the chip. Detection works in reflection.
The sample sits in a clear PMMA chip, backed by a black PMMA layer, directly under the optical channels.
In direct contact with the chip through thermal grease. A thermistor at the heater feeds a PID loop on the ESP32 that holds 65°C within ±0.5°C.
Loading CAD model
Board models from the team's Altium CAD. Chip, heating plate and the stacked layout are simplified.
Results
- Holds 65°C within ±0.5°C
- Running on fabricated hardware, validated subsystem by subsystem
Fluorescence sensing
What
The optical readout. A 470 nm LED excites the sample; if the DNA amplified it fluoresces, and photodiodes and AS7341 spectral sensors pick up the light.
Why
Fluorescence is the result itself, so the signal has to be clean enough to call a sample positive or negative.
How
- Validated the optical path in Zemax: LED-to-sample excitation, sensor placement, and stray light and crosstalk
- Designed the fluorescence sensing PCB with four AS7341 spectral sensors and a fifth color channel behind a TCA9548A I2C multiplexer, two PWM-driven 470 nm LEDs and a 1.8V LDO
- On the NAAT module, each of four channels pairs a blue LED with a Vishay TEMD6200 photodiode, reading in reflection
- Zemax
- AS7341
- TCA9548A
- I2C
- Photodiodes
- 470 nm LEDs
- PCB design
Illustrative model. Curve shapes, times and which channel reads which target are not measured data.
Results
- Optical path validated in Zemax before fabrication
- Fluorescence board fabricated and brought up
- Validating results on real hardware with a wet lab
PCBs and power
What
The PCBs that tie the system together, including battery and solar power, taken from a blank board to bring-up.
Why
A device for clinics without a lab or reliable power has to run from its own battery and recharge from the sun.
How
- Designed the control, sensing and power boards around an ESP32, with USB-C and solar charging for a 3.7V 5000 mAh LiPo and a 3.3V regulator
- Brought up every board myself after fabrication
- Budgeted power: 4.45 W worst case with the heater on, 1.69 Wh per 20-minute reading, about 37 hours to refill by solar
- Housed the NAAT and fluorescence modules in one printed enclosure, 119 x 86.56 mm
- PCB design
- ESP32
- LiPo charging
- Solar charging
- USB-C
- Power budgeting
- Board bring-up
- 3D printing
Results
- About $57 in parts for the whole device, $3.08 per test
- 9.1% of the battery per 20-minute reading
- Boards fabricated and brought up
From the build
One platform, two assays
NAAT for Zika, dengue and malaria. A fluorescence module for HE4, LYVE-1, PSA, KIM-1 and NGAL. Both share the power board and one printed housing.
Toward the clinic
Mapped the regulatory path: a Class II in vitro diagnostic on the 510(k) pathway, under 21 CFR 820 design controls, ISO 13485 and ISO 14971.