Label-free and enzyme-free fluorescent isocarbophos aptasensor based on MWCNTs and G-quadruplex.

A novel label-free and enzyme-free detection strategy has been developed for the fluorescent detection of isocarbophos (ICP) using multi-walled carbon nanotubes (MWCNTs) and G-quadruplex as the signal transducers. In this work, the split ICP aptamer were attached to a G-quadruplex motif at their respective terminals. In the presence of ICP, the split aptamers could undergo conformational change into a sandwiched-like ternary complex, which prevent them from adsorbing to the MWCNTs due to the increased steric hindrance. As a result, the fluorescence signal of the G-quadruplex probes N-methyl mesoporphyrin IX (NMM) was enhanced significantly. In the absence of ICP, the split aptamer only existed in the form of single-stranded DNA, which could be easily adsorbed by MWCNTs and resulted in a quenched fluorescence signal of NMM. The proposed strategy could selectively and sensitively detect ICP with a detection limit of 10 nM. Furthermore, we have also demonstrated the capability of this strategy in the detection of ICP in real samples from vegetable extract, indicating the potential application of this strategy in food safety issues.