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Tear down and analysis of Lucira Check It COVID-19 Test Device

calendar_today Oct 20, 2024 • person DIYLABTECH

Introduction

The Lucira COVID-19 Check It test gained prominence as the first molecular test to receive FDA Emergency Use Authorization (EUA) for at-home COVID-19 detection. Its simplicity is noteworthy: a nasal swab sample is collected, placed in a vial with pre-loaded reagents, and after 30 minutes in the reader equipment, the result is displayed via LEDs.

Initial impressions:

  1. The device uses non-rechargeable batteries, intended for single use. This design choice significantly reduces complexity, bill of materials, and overall price, impacting the company's profitability.
  2. The self-contained nature of the device is impressive, eliminating the need for external resources like electricity or smartphone apps, which have become common in Point-of-Care (PoC) diagnostic devices.

These factors position the Lucira test as one of the best, if not the best, PoC devices available for molecular testing of COVID-19. This reputation likely contributed to its fame, financial success, and subsequent acquisition offer from Pfizer.

Technology Behind Lucira's COVID-19 Test

Lucira employs RT-LAMP (Reverse Transcription Loop-mediated Isothermal Amplification) technology. Unlike traditional PCR tests, RT-LAMP doesn't require temperature cycling, making it faster and simpler. This technology enables Lucira to offer the equipment and necessary reagents for just $55, a significant democratization of molecular tests for at-home use. For comparison, PCR equipment alone typically costs thousands of dollars. The trade-off is that the $55 Lucira test is single-use, with the device, reagents, and consumables discarded after testing.

Prior Work and Gaps in Understanding

Several enthusiasts have explored the device's working mechanism, but gaps in understanding remain:

  1. Nava Whiteford examined the device based on Brad Ackerman's teardown images posted on Twitter. However, the microfluidic aspects, particularly reagent storage, were unclear from the blog post.
  2. A YouTube video by Yyy provided an excellent teardown of the device but couldn't fully explain the main diagnostic mechanism or multiplexing aspects.

This analysis aims to address these gaps, exploring why the device isn't reusable and detailing its overall functionality. We'll utilize publicly available teardown images, videos, and patents to understand the equipment's workings.

Device Components and Functionality

Shell

The shell consists of two simple parts. The grooves are crucial for inserting the vial with enough force to puncture it, releasing the sample into the reaction chamber.

PCB (Printed Circuit Board)

The PCB is a critical component of the Lucira test, incorporating several key elements:

  1. Heating element: Made of exposed copper tracks, it provides constant temperature for incubation, controlled by an STM32 microcontroller.
  2. LEDs: Eight LEDs are used for readout of the color change after the reaction, indicating that Lucira's test uses colorimetric LAMP.
  3. Light sensor: Located at the center of the PCB heater, it detects color changes in the sample.

Reaction Chamber

The reaction chamber is a complex, multi-layered structure:

  1. Black plastic outer part: Prevents ambient light interference.
  2. Silicon gasket at the top: Prevents fluid leaks.
  3. Transparent microfluidic part: Where the reaction occurs.
  4. Bottom elastic part: Prevents fluid from spilling onto the PCB, avoiding potential short circuits.

When the sample vial is placed on the reader, it's punctured at the bottom, releasing fluids into the microfluidic cassette. The cassette comprises four crucial parts:

  1. Top black plastic layer: Contains a metallic puncture and central hole for fluid flow.
  2. Eight vents: Allow air to escape from microfluidic chambers.
  3. White absorbent pads: Prevent fluid leakage and contain lyophilized reagents.
  4. Transparent microfluidic cell: Serves as both fluid chambers and light guides.

The transparent part's dual function as microfluidic cell and light guide allows for compact packaging of optoelectronic components and heaters on a single PCB, reducing manufacturing costs.

Optical Detection System

The device uses a clever optical system:

  • Light from LEDs passes through light-pipes and fluid chambers.
  • Color changes in the sample are detected using appropriately chosen LED colors.
  • The thin walls and fluid layers in the microfluidics increase test sensitivity.

The eight microfluidic chambers serve multiple purposes:

  1. Positive and negative controls
  2. Human genome detection to ensure proper sample collection
  3. Potential for multiplexing other diseases (e.g., Flu or strep detection)

PCB Design Considerations

  • The PCB features several cuts, likely to isolate heat from the heating element.
  • Two large pads act as battery contacts.
  • Eight testing pads on the bottom are probably used for QC and firmware updates.

Room for Improvement

  1. Reusability: The single-use nature of the device is a significant drawback. A potential improvement could be making only the reaction chamber and vial single-use, similar to Cue Health's approach.
  2. Power source: Replacing AA batteries with a USB-C power connection could enhance reusability and align with competitor offerings.
  3. Real-time data access: Implementing Bluetooth connectivity to access photodiode data in real-time via a smartphone app could make the device a true RT-LAMP system.

However, these improvements may conflict with Lucira's initial goal of providing a self-sufficient molecular diagnostic device that doesn't rely on external equipment or devices.

Cost Analysis

A rough breakdown of the bill of materials (BOM) suggests a total cost of $9-12 per device. With a retail price of $55, this represents a healthy 5X markup, which is generally good from a business perspective.

Closing Remarks

Despite its innovative design and initial success, Lucira faced financial challenges like many diagnostic companies that boomed during the pandemic. The company went bankrupt in 2022 but was subsequently acquired by Pfizer in 2023, potentially giving it a new lease on life.

The Lucira test uses loop-mediated isothermal amplification (LAMP) technology, which amplifies the virus' genetic material. A positive test result causes a pH change, triggering an LED indicator on the device.

Lucira Health, formerly known as Diassess, initially focused on developing an at-home flu test with funding from the US Biomedical Advanced Research and Development Authority. The company pivoted to COVID-19 testing when the pandemic began, showcasing its ability to adapt to urgent public health needs.