All-printed semiquantitative paper-based analytical devices relying on QR code array readout.

Area of Science:

• Analytical Chemistry
• Biomedical Engineering
• Materials Science

Background:

• Smartphones and QR codes are increasingly used in diverse applications, now extending to point-of-care testing (POCT).
• Traditional paper-based analytical devices (PADs) often require complex readout methods or digital analysis.
• There is a need for simple, accessible, and cost-effective diagnostic tools for POCT.

Purpose of the Study:

• To develop a novel semiquantitative assay readout for paper-based analytical devices (PADs) using smartphone-based QR code recognition.
• To integrate "distance-based" colorimetric signaling with QR code technology for analyte detection.
• To demonstrate a POCT method that eliminates the need for digital color analysis or custom hardware.

Main Methods:

• Designed PADs with an array of QR codes within a paperfluidic channel.
• Developed a mask dye concept to initially conceal QR codes, enabling "unmasking" via color change.
• Fabricated devices using commercial inkjet and solid ink printing, optimizing mask dye opacity.
• Evaluated a model assay for colorimetric copper ion (Cu2+) detection (0.4 mM to 3.2 mM).

Main Results:

• Achieved semiquantitative readout by unmasking QR codes through indicator color changes.
• Demonstrated consistent and reproducible results across different smartphone models and lighting conditions.
• Validated the assay for copper ion detection using a free smartphone barcode reader app.
• Confirmed the novelty as the first semiquantitative assay relying solely on QR code readout without digital color analysis.

Conclusions:

• Successfully integrated QR code recognition with colorimetric signaling in PADs for POCT.
• Presented a cost-effective and user-friendly semiquantitative assay readout method.
• This approach offers a promising alternative for accessible diagnostics, leveraging ubiquitous smartphone technology.