Figure 4.

Principle of loop-mediated isothermal amplification. This figure was drawn using biorender software online (https://app.biorender.com/). (A) The initial phase. The F2 sequence of FIP binds to F2c, and F3 binds to F3c and extends to displace the complete complementary single strand. F1c on FIP and Fl on this single strand are complementary structures that self-base pair to form a ring structure. BIP and B3 successively initiate synthesis, similar to FIP and F3. (B) The amplification cycle phase. Using the stem-loop structure as a template, FIP binds to the F2c region of the stem-loop to initiate strand displacement synthesis, and B2 on the BIP primer binds to B2 to initiate a new round of amplification. Two loop primers, LooF and LooB also combined with the stem-loop structure to initiate strand displacement synthesis, respectively, and the cycle began again.