Visualized Quantitation of Trace Nucleic Acids Based on the Coffee-Ring Effect on Colloid-Crystal Substrates

Area of Science:

• Biotechnology
• Analytical Chemistry
• Materials Science

Background:

• Nucleic acid amplification tests (NAATs) are crucial for molecular diagnostics.
• Quantitative detection of trace DNA remains challenging.
• The coffee-ring effect is a phenomenon observed during the drying of colloidal droplets.

Purpose of the Study:

• To develop a visualized, quantitative detection method for NAATs.
• To utilize the coffee-ring effect on colloid-crystal substrates for DNA quantification.
• To establish a sensitive and rapid assay for trace DNA detection.

Main Methods:

• Loop-mediated isothermal amplification (LAMP) of DNA was performed.
• The LAMP solution was drop-cast onto a colloid-crystal substrate and allowed to dry.
• The width of the resulting coffee ring, containing magnesium pyrophosphate, was measured.
• A smartphone was used for quantitative readout.

Main Results:

• A linear correlation was observed between coffee-ring width and the logarithm of initial DNA concentration.
• Colloid-crystal substrates demonstrated high sensitivity for the assay.
• The assay required only 0.50 μL of sample and was completed in 5 minutes.
• A limit of detection of 20 copies of DNA was achieved using smartphone analysis.

Conclusions:

• A novel, visualized, and quantitative method for DNA detection based on the coffee-ring effect was successfully developed.
• The colloid-crystal substrate facilitates a highly sensitive and rapid assay for trace DNA.
• The developed assay offers a promising tool for point-of-care nucleic acid detection.