Melamine-Mediated Base Mismatch for Label-Free and Amplified Sensitive Fluorescent Detection of Melamine in Milk

Sensitive identification and detection of melamine illegally added to food to increase false protein content is important for food safety monitoring because melamine can cause tissue injury or even death above the safety regulation level. Melamine can coordinate with two thymines to form stable T-melamine-T structures. On the basis of such a unique interaction, we have developed a T-melamine-T base mismatch-mediated rolling circle amplification (RCA) signal enhancement means for amplified sensitive and label-free fluorescent detection of melamine in milk. The presence of melamine facilitates the hybridization between two T:T base mismatch containing DNA strands, which triggers RCA generation of many long sequences with repeated G-quadruplex segments. The fluorescent dye, thioflavin T, further binds the resulting G-quadruplexes to exhibit substantially enhanced fluorescence for sensitive detection of melamine at the low nanomolar level in a label-free manner. Besides, the developed approach is highly selective toward the discrimination and detection of melamine in milk samples.