A lateral flow assay for copper(II) utilizing catalytic and stem-loop based signal amplification

A DNAzyme-based catalytic and stem-loop based amplification scheme is used in a Cu(II)-specific lateral flow assay (LFA). Three test lines with given cut-off value on the test strip are set as the signal indicating zone for semiquantitative analysis by the number of red color bands that appear after lateral flow. The colored bands are generated by accumulation of gold nanoparticles. Four detection ranges can be visualied: (a) 0–2 ng·mL−1 (= negative); 2–50 ng·mL−1; 50–200 ng·mL−1 and > 200 ng·mL−1 of Cu(II) (= positive). The visual detection limit is thus considered as being 2 ng·mL−1 which is much lower than the U.S. EPA limit in drinking water (1.25 μg·mL−1). The highly specific DNAzyme, the strong multiple-turnover catalytic target recycling property and highly efficient amplification strategy warrant the high specificity, sensitivity and rapidity of this LFA. Conceivbly, this detecton scheme can be extended to other metal ions by proper choice of the ion-specific DNAzyme.