Optimization of real-time colorimetric LAMP assay. (A) Detection mechanism of real-time colorimetric LAMP assay based on synergistic enhancement effect of H+ and PPi- ions, two byproducts of LAMP reaction. (B) Comparison of color change between positive control (PC) (1 × 104 copies HPV 16 DNA template) and negative control (NC) (no DNA template) in colorimetric LAMP assay with: i) non-buffered LAMP reaction solution, and ii) commercially available NEB LAMP reaction buffer. Inner images are the corresponding photos of PC and NC samples. (C) Effect of different metal ion indicators on the colorimetric LAMP assay. (D) Effect of different Mg2+ ion concentration on the colorimetric LAMP assay.