A New Multifunctional Biosensor Based on a Hairpin Oligonucleotide Probe and G-Quadruplex/Hemin DNAzyme

A new multifunctional fluorescent "turn-on" biosensor was constructed based on a guanine-rich hairpin probe and G-quadruplex/hemin DNAzyme. The probe was labeled with quencher and fluorescein at 5' and 3' terminus, respectively. In the absence of the target, the probe form hairpin structure and the fluorescence of the fluorescein was quenched by the quencher. However, in the presence of the target, the hairpin structure transformed to G-quadruplex and the fluorescence was recovered. By monitoring the fluorescence of the probe before and after combining with the target, both hemin and hemoglobin were detected rapidly and conveniently with high sensitivity. The limit of detection for hemin and hemoglobin were estimated to be 283 pmol/L and 109 pmol/L, respectively. The specific interaction between the DNA probe and hemin were investigated via absorption and fluorescence spectra. Furthermore, L-cysteine was detected with naked eyes based on the peroxidase-like activity of the new G-quadruplex/hemin DNAzyme. The limit of detection for L-cysteine was estimated to be 3.6 mu mol/L, which was lower than the normal level of intracellular L-cysteine (30-200 mu mon). The method developed here was rapid, simple and sensitive for detection of hemin, hemoglobin and L-cysteine, demonstrating great potential in bioanalysis, drug screening, and disease diagnosis.