Label-free Pb detection on the layer-by-layer platform using real-time dual polarization interferometry.

Contamination of Lead ion (Pb) poses a serious threat to human health and the environment. Developing sensitive and reliable Pb biosensor is essential and significant for prevention and control of the water pollution. In this work, we utilized the direct conformational signal changes in specific interaction process between Pb and guanine-rich (G-rich) oligonucleotides to establish a sensing system. The binding of Pb and G-rich oligonucleotides results in conformational transition from single strand to G-quadruplex, which was recorded real-time by dual polarization interferometry (DPI). The sensing platform was established via layer-by-layer assembly strategy that employing polyethyleneimine and ploythymine as media layers to link the G-rich DNA on the DPI chip, which is simple, facile and without need of synthesizing sophisticated nanomaterial. On the basis of above sensing platform and quantifiable conformational changes, a simple, sensitive, specific and label-free Pb biosensor was established. This research provides us a simple and sensitive method for detection of ions, also encourages us to combine surface technique to biosensing application and explore the relationship between structures and functions.